Find a PhD Project Here
Opportunities for fully funded PhD or EngDoc research projects are available in all fields of research within the School. You may search for current projects on this page. APPLY HERE for a PhD Place.
PhD in Photonics
PhD in Condensed Matter
PhD in Astrophysics
Search current PhD opportunities in the School of Physics & Astronomy:-
Condensed Matter
Characterization of Triplet Superconductivity by Tunneling Spectroscopy
Wahl, Dr Peter - gpw2@st-andrews.ac.uk
In spin-triplet superconductors, cooper pairs are formed by electrons whose spins are aligned parallel. Examples of superconductors, where the electron pairing occurs with equal spins are Sr2RuO4 and some of the heavy fermion superconductors (e.g. ferromagnetic superconductors). In most of these materials, the superconducting order parameter and the properties of the superconducting state are only poorly understood. Part of the experimental challenge is that superconductivity typically only emerges at temperatures on the order of 1K. The properties of these superconductors are often intriguing and surprising, e.g. in ferromagnetic superconductors the material is at the same time magnetic and superconducting. Even without applied magnetic field, the superconductor can be expected to be in a vortex state due to the magnetization of the material itself.
During the first time of this project, the focus of your work will be to establish the sample preparation and to identify a triplet superconductor which is suitable for studies by spectroscopic imaging STM. In parallel, you will be trained to operate our spectroscopic imaging STM, which is mounted in a dilution refrigerator and can reach a base temperature of 7mK. The first part of this project will be carried out at the Max-Planck-Institute for Solid State Research, Stuttgart, Germany.
In spin-triplet superconductors, cooper pairs are formed by electrons whose spins are aligned parallel. Examples of superconductors, where the electron pairing occurs with equal spins are Sr2RuO4 and some of the heavy fermion superconductors (e.g. ferromagnetic superconductors). In most of these materials, the superconducting order parameter and the properties of the superconducting state are only poorly understood. Part of the experimental challenge is that superconductivity typically only emerges at temperatures on the order of 1K. The properties of these superconductors are often intriguing and surprising, e.g. in ferromagnetic superconductors the material is at the same time magnetic and superconducting. Even without applied magnetic field, the superconductor can be expected to be in a vortex state due to the magnetization of the material itself.
During the first time of this project, the focus of your work will be to establish the sample preparation and to identify a triplet superconductor which is suitable for studies by spectroscopic imaging STM. In parallel, you will be trained to operate our spectroscopic imaging STM, which is mounted in a dilution refrigerator and can reach a base temperature of 7mK. The first part of this project will be carried out at the Max-Planck-Institute for Solid State Research, Stuttgart, Germany.
Competing and Coexisting orders in Fe-based Superconductors
Wahl, Dr Peter - gpw2@st-andrews.ac.uk
The iron-based superconductors, an only recently discovered family of materials which become superconducting at temperatures up to ~50K, have almost all complex phase diagrams as a function of doping with structural and magnetic phase transitions. Superconductivity in these materials, similarly to high-temperature copper based superconductors, is most likely not mediated by phonon coupling, but rather either by some magnetically mediated coupling or due to electron correlations. In this regard, the importance of the magnetic and structural phases in these materials for superconductivity, and whether they coexist or compete with superconductivity become important questions. In this project, the aim is to determine the importance and possibly the origin of symmetry breaking electronic ordering for superconductivity. A nematic state in an iron-based superconductor has been first observed by STM in CaFe1.94Co0.06As2[1]. By spectroscopic imaging STM, you will attempt to search for ordering phenomena in the electronic excitations and study their dependence on temperature and magnetic field, in order to elucidate their relation to superconductivity. The first part of this project will be carried out at the Max-Planck-Institute for Solid State Research, Stuttgart, Germany.
T.-M. Chuang, M.P. Allan, J. Lee, Y. Xie, N. Ni, S.L. Bud’ko, G.S. Boebinger, P.C. Canfield, and J.C. Davis, Science 327, 181 (2010).
The iron-based superconductors, an only recently discovered family of materials which become superconducting at temperatures up to ~50K, have almost all complex phase diagrams as a function of doping with structural and magnetic phase transitions. Superconductivity in these materials, similarly to high-temperature copper based superconductors, is most likely not mediated by phonon coupling, but rather either by some magnetically mediated coupling or due to electron correlations. In this regard, the importance of the magnetic and structural phases in these materials for superconductivity, and whether they coexist or compete with superconductivity become important questions. In this project, the aim is to determine the importance and possibly the origin of symmetry breaking electronic ordering for superconductivity. A nematic state in an iron-based superconductor has been first observed by STM in CaFe1.94Co0.06As2[1]. By spectroscopic imaging STM, you will attempt to search for ordering phenomena in the electronic excitations and study their dependence on temperature and magnetic field, in order to elucidate their relation to superconductivity. The first part of this project will be carried out at the Max-Planck-Institute for Solid State Research, Stuttgart, Germany.
T.-M. Chuang, M.P. Allan, J. Lee, Y. Xie, N. Ni, S.L. Bud’ko, G.S. Boebinger, P.C. Canfield, and J.C. Davis, Science 327, 181 (2010).
Controllable topological phase transitions
King, Dr Phil - pdk6@st-andrews.ac.uk
Topological insulators are a fundamentally new form of quantum matter with striking properties, such as unusual spin-polarized metallic surface states. They are potential platforms to realize a range of fundamental and practical advances, including dissipationless transport and quantum computation. Controlling the transition between conventional band insulators and topological insulators is key to realizing their potential. Moreover, it is a rare example of a phase transition not characterized by symmetry breaking, the mainstay of condensed matter physics, but rather it is rooted in the mathematical concept of topology. In this project, you will explore new ways to exploit this in condensed matter systems. You will investigate methods to drive topological phase transitions, and study the interplay of topological order with additional phases such as superconductivity or magnetism. You will use angle-resolved photoemission spectroscopy (ARPES), a powerful probe of electronic structure, to track the evolution of the bulk band structure and the emergence of helical surface states. You will make extensive use of our state-of-the-art spectroscopy lab in St Andrews, and will also perform measurements at synchrotrons in the UK, Europe and the USA.
Topological insulators are a fundamentally new form of quantum matter with striking properties, such as unusual spin-polarized metallic surface states. They are potential platforms to realize a range of fundamental and practical advances, including dissipationless transport and quantum computation. Controlling the transition between conventional band insulators and topological insulators is key to realizing their potential. Moreover, it is a rare example of a phase transition not characterized by symmetry breaking, the mainstay of condensed matter physics, but rather it is rooted in the mathematical concept of topology. In this project, you will explore new ways to exploit this in condensed matter systems. You will investigate methods to drive topological phase transitions, and study the interplay of topological order with additional phases such as superconductivity or magnetism. You will use angle-resolved photoemission spectroscopy (ARPES), a powerful probe of electronic structure, to track the evolution of the bulk band structure and the emergence of helical surface states. You will make extensive use of our state-of-the-art spectroscopy lab in St Andrews, and will also perform measurements at synchrotrons in the UK, Europe and the USA.
Exciton Diffusion in Organic Semiconductors
Samuel, Prof Ifor - idws@st-andrews.ac.uk
The discovery of semiconducting properties in organic materials has opened major new directions in semiconductor physics. Organic semiconductors combine the simple fabrication and tuning of properties that is typical of plastics with novel optoelectronic properties useful for devices such as light-emitting diodes and solar cells. The low-dimensional nature of these materials means that excitons (electron-hole pairs) are strongly bound even at room temperature and play a very important role in their physics. Whilst charge transport has been widely studied, exciton transport has been largely overlooked. We have now developed techniques based on time-resolved spectroscopy that allow the measurement of exciton diffusion. We now wish to apply them to understand the physics of exciton diffusion and the factors controlling it. A breakthrough in this field could in turn lead to a breakthrough in the efficiency of organic solar cells.
The discovery of semiconducting properties in organic materials has opened major new directions in semiconductor physics. Organic semiconductors combine the simple fabrication and tuning of properties that is typical of plastics with novel optoelectronic properties useful for devices such as light-emitting diodes and solar cells. The low-dimensional nature of these materials means that excitons (electron-hole pairs) are strongly bound even at room temperature and play a very important role in their physics. Whilst charge transport has been widely studied, exciton transport has been largely overlooked. We have now developed techniques based on time-resolved spectroscopy that allow the measurement of exciton diffusion. We now wish to apply them to understand the physics of exciton diffusion and the factors controlling it. A breakthrough in this field could in turn lead to a breakthrough in the efficiency of organic solar cells.
Exotic Kondo effects in tunable nanostructures
Hooley, Dr Chris - cah19@st-andrews.ac.uk
When a magnetic impurity (such as iron) is placed in a good metal, it causes anomalously strong scattering of the conduction electrons below a certain characteristic temperature. This effect is called the Kondo effect, and the associated temperature is therefore called the Kondo temperature. We now understand that what the magnetic impurity is trying to do is to bind the conduction electrons into a spin-singlet, and at sufficiently low temperatures, this is achieved. In 1998, the effect was observed for the first time in nanophysical systems, with a quantum dot playing the role of the magnetic impurity, and the two electrical leads playing the role of the conduction sea. Quantum dot systems are, however, much more tunable than the metals and impurities offered to us by chemistry: even the dimensionality of the leads can in principle be altered. This is an exciting prospect, since we know that in one dimension the interacting electron system adopts an unusual strongly correlated state called a Luttinger liquid, and that the theory of the Kondo effect with Luttinger liquid leads is quite different to that in the normal metal case. This theoretical project aims to address the following questions:
- Can the Luttinger-liquid Kondo effect be realised in quantum dot systems?
- How do its properties relate to those of the soft-gap Anderson model?
- What is its behaviour at bias voltages well above the Kondo scale?
- Does it have a critical point, and if so, can this be characterised?
Established relations with several experimental groups active in the field (e.g. the Grayson group at the Walter Schottky Institute, the Marcus group at Harvard, and the Kouwenhoven group at Delft) are expected to provide fruitful and up-to-date experimental information. The majority of the work will consist of pen-and-paper calculations, perhaps supplemented by some computational analysis.
When a magnetic impurity (such as iron) is placed in a good metal, it causes anomalously strong scattering of the conduction electrons below a certain characteristic temperature. This effect is called the Kondo effect, and the associated temperature is therefore called the Kondo temperature. We now understand that what the magnetic impurity is trying to do is to bind the conduction electrons into a spin-singlet, and at sufficiently low temperatures, this is achieved. In 1998, the effect was observed for the first time in nanophysical systems, with a quantum dot playing the role of the magnetic impurity, and the two electrical leads playing the role of the conduction sea. Quantum dot systems are, however, much more tunable than the metals and impurities offered to us by chemistry: even the dimensionality of the leads can in principle be altered. This is an exciting prospect, since we know that in one dimension the interacting electron system adopts an unusual strongly correlated state called a Luttinger liquid, and that the theory of the Kondo effect with Luttinger liquid leads is quite different to that in the normal metal case. This theoretical project aims to address the following questions:
- Can the Luttinger-liquid Kondo effect be realised in quantum dot systems?
- How do its properties relate to those of the soft-gap Anderson model?
- What is its behaviour at bias voltages well above the Kondo scale?
- Does it have a critical point, and if so, can this be characterised?
Established relations with several experimental groups active in the field (e.g. the Grayson group at the Walter Schottky Institute, the Marcus group at Harvard, and the Kouwenhoven group at Delft) are expected to provide fruitful and up-to-date experimental information. The majority of the work will consist of pen-and-paper calculations, perhaps supplemented by some computational analysis.
Experimental and Theoretical Investigation of Spatially Modulated Magnetic Phases Near to Quantum Criticality
Huxley, Prof Andrew - ah311@st-andrews.ac.uk
The possibility of magnetic spin-crystals formed by the superposition of helical spin modulations with different wave-vectors has been a subject of much recent experimental and theoretical work. Signatures of phases with this property have been found in an array of materials including MnSi and Sr3Ru2O7. On the theoretical side, there are several ways in which such states might form. These include the formation of spiral modulation due to a Dzyalosinskii-Moriya spin-orbit interaction in itinerant magnets, residual, small-wavevector nesting due to the electron dispersion in a lattice [1,2] and from competing interactions that can give rise to a series of transitions forming a Devil's Staircase [3]. Perhaps the most intriguing suggestion - and one that has most captured the imagination of condensed matter theorists of late - is that an itinerant system on the brink of a quantum phase transition might possess an intrinsic instability to the formation of modulated magnetic phases [4]. In any particular material, one or more of these effects may operate with the possibility of a complicated interplay between them.
This project aims to investigate the phenomenon of spatially modulated magnetism from both an experimental and theoretical perspective. We will use techniques of quantum many-body physics and field theory to investigate the possibility of spatially modulated magnetism in real systems. These investigations will be carried out in concert with neutron scattering experiments to provide inspiration for and validate this theory. The experimental part will include growing the crystals for these experiments as well as performing the measurements. We anticipate that a student will spend approximately 2/3 of their time on theory and 1/3 on experimental work, working both in Edinburgh and St Andrews as well as at international facilities.
[1] A. M. Berridge, A. G. Green, S. A. Grigera and B. D. Simons "A Magnetic Analogue of the of the FFLO state: Inhomogeneous Instabilities Near to Tricritical Points" Physical Review Letters 102, 149903 (2009).
[2] G. J. Conduit, A. G. Green, and B. D. Simons, "Inhomogeneous phase formation on the border of itinerant ferromagnetism" Physical Review Letters 103, 207201 (2009) [spotlighted in Physics 2, 93 (2009)]
[3] P. Bak & J. von Boehm, "Ising model with solitons, phasons, and 'the devil's staircase'", Phys Rev B 21 5297 (1980)
[4] J. Rech C.Pépin, V.Chubukov, "Quantum critical behaviour in intinerant electron systems: Eliashberg theory and instability of a ferromagentic quantum critical point" Phys Rev B 74 195126 (2006)
The possibility of magnetic spin-crystals formed by the superposition of helical spin modulations with different wave-vectors has been a subject of much recent experimental and theoretical work. Signatures of phases with this property have been found in an array of materials including MnSi and Sr3Ru2O7. On the theoretical side, there are several ways in which such states might form. These include the formation of spiral modulation due to a Dzyalosinskii-Moriya spin-orbit interaction in itinerant magnets, residual, small-wavevector nesting due to the electron dispersion in a lattice [1,2] and from competing interactions that can give rise to a series of transitions forming a Devil's Staircase [3]. Perhaps the most intriguing suggestion - and one that has most captured the imagination of condensed matter theorists of late - is that an itinerant system on the brink of a quantum phase transition might possess an intrinsic instability to the formation of modulated magnetic phases [4]. In any particular material, one or more of these effects may operate with the possibility of a complicated interplay between them.
This project aims to investigate the phenomenon of spatially modulated magnetism from both an experimental and theoretical perspective. We will use techniques of quantum many-body physics and field theory to investigate the possibility of spatially modulated magnetism in real systems. These investigations will be carried out in concert with neutron scattering experiments to provide inspiration for and validate this theory. The experimental part will include growing the crystals for these experiments as well as performing the measurements. We anticipate that a student will spend approximately 2/3 of their time on theory and 1/3 on experimental work, working both in Edinburgh and St Andrews as well as at international facilities.
[1] A. M. Berridge, A. G. Green, S. A. Grigera and B. D. Simons "A Magnetic Analogue of the of the FFLO state: Inhomogeneous Instabilities Near to Tricritical Points" Physical Review Letters 102, 149903 (2009).
[2] G. J. Conduit, A. G. Green, and B. D. Simons, "Inhomogeneous phase formation on the border of itinerant ferromagnetism" Physical Review Letters 103, 207201 (2009) [spotlighted in Physics 2, 93 (2009)]
[3] P. Bak & J. von Boehm, "Ising model with solitons, phasons, and 'the devil's staircase'", Phys Rev B 21 5297 (1980)
[4] J. Rech C.Pépin, V.Chubukov, "Quantum critical behaviour in intinerant electron systems: Eliashberg theory and instability of a ferromagentic quantum critical point" Phys Rev B 74 195126 (2006)
Holographic traps and guides for superfluidity studies and atom interferometry
Cassettari, Dr Donatella - dc43@st-andrews.ac.uk
Holographic traps are a new kind of optical traps for neutral atoms which are promising for a wide range of applications, e.g. quantum information processing and quantum simulation. They are produced by diffracting a laser beam off a computer-controlled optical device, known as a Spatial Light Modulator (SLM). This apparatus offers unparalleled flexibility in the choice of trapping geometry, and different experiments can be done simply by reconfiguring the SLM.
In this PhD project you will work on:
- Double well traps for confined atom interferometry, which is promising for the development of sensitive devices (see [1] for a review).
- Ring-shaped atom guides (see [2] and [3]), which can be used to observe superfluid motion of a Bose-Einstein condensate, e.g. persistent current states. BECs in these geometries and the study of their critical velocities (where superflow stops) have very important technological applications in sensing devices, such as superconducting quantum interference devices (SQUIDs). Moreover, theoretical proposals have been put forward in which coherent superposition of different BEC flows can be used as qubits.
[1] http://rmp.aps.org/abstract/RMP/v81/i3/p1051_1
[2] http://prl.aps.org/abstract/PRL/v106/i13/e130401
[3] http://lanl.arxiv.org/abs/1008.2140
Holographic traps are a new kind of optical traps for neutral atoms which are promising for a wide range of applications, e.g. quantum information processing and quantum simulation. They are produced by diffracting a laser beam off a computer-controlled optical device, known as a Spatial Light Modulator (SLM). This apparatus offers unparalleled flexibility in the choice of trapping geometry, and different experiments can be done simply by reconfiguring the SLM.
In this PhD project you will work on:
- Double well traps for confined atom interferometry, which is promising for the development of sensitive devices (see [1] for a review).
- Ring-shaped atom guides (see [2] and [3]), which can be used to observe superfluid motion of a Bose-Einstein condensate, e.g. persistent current states. BECs in these geometries and the study of their critical velocities (where superflow stops) have very important technological applications in sensing devices, such as superconducting quantum interference devices (SQUIDs). Moreover, theoretical proposals have been put forward in which coherent superposition of different BEC flows can be used as qubits.
[1] http://rmp.aps.org/abstract/RMP/v81/i3/p1051_1
[2] http://prl.aps.org/abstract/PRL/v106/i13/e130401
[3] http://lanl.arxiv.org/abs/1008.2140
Holographic traps for the efficient production of Bose-Einstein condensates
Cassettari, Dr Donatella - dc43@st-andrews.ac.uk
Evaporative cooling is an essential stage in the creation of Bose-Einstein condensates (BECs) in atomic gases. Recently we suggested [1] that holographic optical traps can be used to increase the evaporation efficiency, leading to larger BECs. In this PhD project you will implement this scheme, which will result in a simplified apparatus for the productions and subsequent manipulation of BECs.
[1] http://pra.aps.org/abstract/PRA/v84/i5/e053410
Evaporative cooling is an essential stage in the creation of Bose-Einstein condensates (BECs) in atomic gases. Recently we suggested [1] that holographic optical traps can be used to increase the evaporation efficiency, leading to larger BECs. In this PhD project you will implement this scheme, which will result in a simplified apparatus for the productions and subsequent manipulation of BECs.
[1] http://pra.aps.org/abstract/PRA/v84/i5/e053410
Integrated Magnetic Resonance Doctoral Training Centre
Smith, Dr Graham - gms@st-andrews.ac.uk
The new EPSRC Doctoral Training Centre in Integrated Magnetic Resonance is a collaboration between 6 of the UK's leading Universities in Advanced Magnetic Resonance Instrumentation and Techniques and includes St. Andrews, Dundee, Aberdeen, Warwick, Nottingham and Southampton.
The aim is to provide a coherent training program for doctoral students whilst working on new research topics in instrumentation and methodology, associated with Magnetic Resonance Imaging, Electron Magnetic Resonance, Nuclear Magnetic Resonance and Dynamic Nuclear Polarisation (which collectively represent £multi-Billion annual markets). Training is delivered from all centres, through residential workshops and over the Access Grid, primarily in the first two years of study.
Funded 4 year PhDs include fees and maintenance of £14000 (tax free) per annum as well as an enhanced travel budget. All PhDs will have internal and external mentors from other centres.
At St Andrews, PhD projects are available on themes associated with major advances in Electron Magnetic Resonance and Dynamic Nuclear Polarisation and are likely to involve collaborations with other centres and other interdisciplinary groups.
PhD topics are likely to involve a combination of instrumental, methodological and computational techniques that would normally be associated with Basic Technology programs.
Representative PhDs from all 6 centres are listed on www.imr-cdt.ac.uk, but other PhD topics may be available on request.
For PhDs at St Andrews, applications can be made directly to St Andrews or via Warwick where the DTC program is administered.
The new EPSRC Doctoral Training Centre in Integrated Magnetic Resonance is a collaboration between 6 of the UK's leading Universities in Advanced Magnetic Resonance Instrumentation and Techniques and includes St. Andrews, Dundee, Aberdeen, Warwick, Nottingham and Southampton.
The aim is to provide a coherent training program for doctoral students whilst working on new research topics in instrumentation and methodology, associated with Magnetic Resonance Imaging, Electron Magnetic Resonance, Nuclear Magnetic Resonance and Dynamic Nuclear Polarisation (which collectively represent £multi-Billion annual markets). Training is delivered from all centres, through residential workshops and over the Access Grid, primarily in the first two years of study.
Funded 4 year PhDs include fees and maintenance of £14000 (tax free) per annum as well as an enhanced travel budget. All PhDs will have internal and external mentors from other centres.
At St Andrews, PhD projects are available on themes associated with major advances in Electron Magnetic Resonance and Dynamic Nuclear Polarisation and are likely to involve collaborations with other centres and other interdisciplinary groups.
PhD topics are likely to involve a combination of instrumental, methodological and computational techniques that would normally be associated with Basic Technology programs.
Representative PhDs from all 6 centres are listed on www.imr-cdt.ac.uk, but other PhD topics may be available on request.
For PhDs at St Andrews, applications can be made directly to St Andrews or via Warwick where the DTC program is administered.
Investigating novel superconducting ground states in nanofabricated hybrid ferromagnetic-superconducting materials and devices using advanced neutron, muon and synchrotron techniques
Lee, Prof Steve - sl10@st-andrews.ac.uk
The search for novel quantum states of matter in artificial thin-film structures, in which superconducting (S) and ferromagnetic (F) materials are juxtaposed, has reached an exciting and timely stage of development. In the last year a series of new landmark experimental results seem set to herald a period of rapid expansion of interest and activity in the field. This was the pioneering observation by several groups of spin-triplet supercurrents traversing relatively thick F layers [1-3], believed theoretically to be signatures of a novel equal-spin spin-triplet and possibly ‘odd frequency’ superconducting state. This achievement represent the culmination of several years of breakthrough experiments [1-7] in a field whose modern era began almost most a decade ago, with the experimental discovery of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) [8] type states in S-F-S structures [10]. What both the FFLO [8] and the odd-frequency pairing phenomena [9] have in common is that they were predicted to occur theoretically in bulk systems [8,9] but only in state-of-the-art artificial thin-film structures were they finally demonstrated to exist [1-7,10-13]. Modern thin-film growth and large area lithographic patterning open-up an enormous range of further possibilities for engendering novel quantum states of matter via the controlled interaction S and F order on the nanoscale. This capability also offers the promise of designing and engineering hybrid metamaterials (in a similar spirit to electromagnetic metamaterials) with tailored quantum properties. Concurrently there is enormous interest in spintronics, the manipulation of electronic spin for application in novel electronic devices. The structures investigated within this programme marry the fields of mesoscopic superconductivity, novel strongly correlated electron physics and spintronics. By introducing quantum coherence phenomena into spintronic types devices, this also opens up the possibility of non-locality and entanglement, with possible application long-term in quantum computation.
Professor Steve Lee leads an EPSRC funded Critical Mass Grant award (St Andrews, Leeds, Bath, Royal Holloway, ISIS, with partners in PSI ( Swizterland), Cambridge, and Leiden ) that underpins an international research programme that brings together a team with a wide range of relevant expertise to explore the physics of such systems. We make use of some of the most powerful probes in condensed matter physics (scattering and surface probe techniques) in order to throw new light onto the physics of artificial S-F metamaterials, with particular emphasis on spatially–resolved measurements. This combines with state-of-the-art facilities for materials growth and patterning and world leading instrumentation for measurement. The programme is also informed by cutting-edge theory. There are significant opportunities for research students within this collaboration, with excellent access to world leading research facilities (such as Diamond, ISIS, ILL, PSI, SLS). Due to the strong interactions between nodes there is also significant scope for student mobility in order to enhance training and experience. This is all underpinned by access to excellent graduate training bot via the SUPA Graduate School and the additional benefits of the Doctoral Training Centre in condensed matter physics based at St Andrews, Edinburgh and Heriot Watt.
[1] J.W.A. Robinson et al., Science 329 59 (2010).
[2] T.S. Khaire et al., PRL 104, 137002 (2010).
[3] M.S. Anwar et al., PRB 82, 100501 (2010).
[4] R.S. Keizer et al., Nature 439 825 (2006).
[5] J. Wang et al., Nat. Phys. 6 389 (2010).
[6] I. Sosnin et al., PRL 96 157002 (2006).
[7] D. Sprungmann et al., PRB 82, 060505 (2010).
[8] P. Fulde and R.A. Ferrell, PRB 135 A550 (1964);
A.I. Larkin and Y.N. Ovchinnikov, Zh. Eksp.
Teor. Fiz. 47, 1136 (1964).
[9] V.L. Berezinskii, JEPT Lett. 20, 287 (1974).
[10] V.V. Ryazanov et al., PRL 86, 2427 (2001); T. Kontos et al., PRL 89, 137007 (2002).
[11] A.I. Buzdin et al., JETP Letters 35, 178 (1982);
[12] F.S. Bergeret et al., PRL 86, 4096 (2001); Rev. Mod. Phys. 77, 1321 (2005).
[13] M. Eschrig et al., PRL 90, 137003 (2003); M. Eschrig and T. Löfwander, Nature Phys. 4 138 (2008).
The search for novel quantum states of matter in artificial thin-film structures, in which superconducting (S) and ferromagnetic (F) materials are juxtaposed, has reached an exciting and timely stage of development. In the last year a series of new landmark experimental results seem set to herald a period of rapid expansion of interest and activity in the field. This was the pioneering observation by several groups of spin-triplet supercurrents traversing relatively thick F layers [1-3], believed theoretically to be signatures of a novel equal-spin spin-triplet and possibly ‘odd frequency’ superconducting state. This achievement represent the culmination of several years of breakthrough experiments [1-7] in a field whose modern era began almost most a decade ago, with the experimental discovery of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) [8] type states in S-F-S structures [10]. What both the FFLO [8] and the odd-frequency pairing phenomena [9] have in common is that they were predicted to occur theoretically in bulk systems [8,9] but only in state-of-the-art artificial thin-film structures were they finally demonstrated to exist [1-7,10-13]. Modern thin-film growth and large area lithographic patterning open-up an enormous range of further possibilities for engendering novel quantum states of matter via the controlled interaction S and F order on the nanoscale. This capability also offers the promise of designing and engineering hybrid metamaterials (in a similar spirit to electromagnetic metamaterials) with tailored quantum properties. Concurrently there is enormous interest in spintronics, the manipulation of electronic spin for application in novel electronic devices. The structures investigated within this programme marry the fields of mesoscopic superconductivity, novel strongly correlated electron physics and spintronics. By introducing quantum coherence phenomena into spintronic types devices, this also opens up the possibility of non-locality and entanglement, with possible application long-term in quantum computation.
Professor Steve Lee leads an EPSRC funded Critical Mass Grant award (St Andrews, Leeds, Bath, Royal Holloway, ISIS, with partners in PSI ( Swizterland), Cambridge, and Leiden ) that underpins an international research programme that brings together a team with a wide range of relevant expertise to explore the physics of such systems. We make use of some of the most powerful probes in condensed matter physics (scattering and surface probe techniques) in order to throw new light onto the physics of artificial S-F metamaterials, with particular emphasis on spatially–resolved measurements. This combines with state-of-the-art facilities for materials growth and patterning and world leading instrumentation for measurement. The programme is also informed by cutting-edge theory. There are significant opportunities for research students within this collaboration, with excellent access to world leading research facilities (such as Diamond, ISIS, ILL, PSI, SLS). Due to the strong interactions between nodes there is also significant scope for student mobility in order to enhance training and experience. This is all underpinned by access to excellent graduate training bot via the SUPA Graduate School and the additional benefits of the Doctoral Training Centre in condensed matter physics based at St Andrews, Edinburgh and Heriot Watt.
[1] J.W.A. Robinson et al., Science 329 59 (2010).
[2] T.S. Khaire et al., PRL 104, 137002 (2010).
[3] M.S. Anwar et al., PRB 82, 100501 (2010).
[4] R.S. Keizer et al., Nature 439 825 (2006).
[5] J. Wang et al., Nat. Phys. 6 389 (2010).
[6] I. Sosnin et al., PRL 96 157002 (2006).
[7] D. Sprungmann et al., PRB 82, 060505 (2010).
[8] P. Fulde and R.A. Ferrell, PRB 135 A550 (1964);
A.I. Larkin and Y.N. Ovchinnikov, Zh. Eksp.
Teor. Fiz. 47, 1136 (1964).
[9] V.L. Berezinskii, JEPT Lett. 20, 287 (1974).
[10] V.V. Ryazanov et al., PRL 86, 2427 (2001); T. Kontos et al., PRL 89, 137007 (2002).
[11] A.I. Buzdin et al., JETP Letters 35, 178 (1982);
[12] F.S. Bergeret et al., PRL 86, 4096 (2001); Rev. Mod. Phys. 77, 1321 (2005).
[13] M. Eschrig et al., PRL 90, 137003 (2003); M. Eschrig and T. Löfwander, Nature Phys. 4 138 (2008).
Magnetic measurements to probe unconventional superconductors
Huxley, Prof Andrew - ah311@st-andrews.ac.uk
Yelland, Dr Ed - eay1@st-andrews.ac.uk
Magnetism and superconductivity are intimately connected in many so-called heavy fermion metals. A particularly dramatic case is URhGe, where two distinct superconducting regions exist – one coexisting with ferromagnetism, and the other at extremely strong applied magnetic fields that are sufficient to destroy conventional forms of superconductivity. This project will involve developing sensitive magnetic measurement apparatus that will operate at extremes of low temperature, high magnetic field and high pressure, and apply them to study URhGe and other related materials. The aims are both to gain a deeper understanding of how magnetic pairing may lead to superconductivity and to drive the search for new superconducting materials. The project could be based in either St Andrews or Edinburgh.
The project is an integral part of a major research effort to study quantum criticality and unusual quantum ordered phases using a variety of magnetic, electrical and thermal measurement techniques. The apparatus in St Andrews includes a state-of-the-art dilution refrigerator (commissioned December 2007) with a base temperature 10 millikelvin and equipped with a 17 tesla magnet, that will allow coverage of a wide region of experimental parameter space, including applied pressures up to 100 kbar.
The focus for the project is on magnetic measurements including torque magnetometry, field gradient magnetometry and a.c. susceptibility. By combining torque and field-gradient results, the vector magnetic moment can be determined as a function of magnetic field and its angle to the crystallographic axes. This will allow a complete phenomenological (Ginzburg-Landau) description of the magnetism close to the superconducting phase to be constructed, and will provide detailed information about the nature of the magnetic interactions that are important for superconductivity. Another important component of the work will be to use quantum oscillations in various magnetic quantities to study the Fermi surface and how these change approaching and crossing quantum phase transitions.
Yelland, Dr Ed - eay1@st-andrews.ac.uk
Magnetism and superconductivity are intimately connected in many so-called heavy fermion metals. A particularly dramatic case is URhGe, where two distinct superconducting regions exist – one coexisting with ferromagnetism, and the other at extremely strong applied magnetic fields that are sufficient to destroy conventional forms of superconductivity. This project will involve developing sensitive magnetic measurement apparatus that will operate at extremes of low temperature, high magnetic field and high pressure, and apply them to study URhGe and other related materials. The aims are both to gain a deeper understanding of how magnetic pairing may lead to superconductivity and to drive the search for new superconducting materials. The project could be based in either St Andrews or Edinburgh.
The project is an integral part of a major research effort to study quantum criticality and unusual quantum ordered phases using a variety of magnetic, electrical and thermal measurement techniques. The apparatus in St Andrews includes a state-of-the-art dilution refrigerator (commissioned December 2007) with a base temperature 10 millikelvin and equipped with a 17 tesla magnet, that will allow coverage of a wide region of experimental parameter space, including applied pressures up to 100 kbar.
The focus for the project is on magnetic measurements including torque magnetometry, field gradient magnetometry and a.c. susceptibility. By combining torque and field-gradient results, the vector magnetic moment can be determined as a function of magnetic field and its angle to the crystallographic axes. This will allow a complete phenomenological (Ginzburg-Landau) description of the magnetism close to the superconducting phase to be constructed, and will provide detailed information about the nature of the magnetic interactions that are important for superconductivity. Another important component of the work will be to use quantum oscillations in various magnetic quantities to study the Fermi surface and how these change approaching and crossing quantum phase transitions.
Mesoscopic unconventional superconductors and Fermi liquids
Mackenzie, Prof Andy - apm9@st-andrews.ac.uk
This project is offer in conjunction with Prof. Amir Yacoby at Harvard.
In this project, we aim to bridge the gap between two fields in which huge progress has been made over the past twenty years. In mesoscopic physics, the aim is to work with samples that are specially fabricated so that their physical size becomes comparable with one or more of the fundamental length scales of the underlying physics. In a metal this might be the mean free path, and in a superconductor it might be the coherence length or the penetration depth. So far, the vast majority of research into mesoscopic physics has been performed on traditional materials in which the electron-electron interactions are relatively weak. In parallel with these developments, equally rapid progress has been made on research into new materials with very strong electron-electron interactions, which lead to high quasiparticle masses and an exciting variety of metallic, superconducting and magnetic ground states. For technical reasons the two fields have advanced in parallel, with little cross-fertilisation of ideas and techniques. The goal of this jointly supervised project is to combine the different expertise of our two groups to bring strongly interacting electrons into the mesoscopic regime. You will work both in St Andrews and at the spectacular new Harvard Nanoscience Center, performing pioneering experiments on the fabrication and measurement of correlated electron mesoscopic devices.
(Jointly affiliated to both University of St Andrews and Max Planck Institute for the Chemical Physics of Solids, Dresden)
This project is offer in conjunction with Prof. Amir Yacoby at Harvard.
In this project, we aim to bridge the gap between two fields in which huge progress has been made over the past twenty years. In mesoscopic physics, the aim is to work with samples that are specially fabricated so that their physical size becomes comparable with one or more of the fundamental length scales of the underlying physics. In a metal this might be the mean free path, and in a superconductor it might be the coherence length or the penetration depth. So far, the vast majority of research into mesoscopic physics has been performed on traditional materials in which the electron-electron interactions are relatively weak. In parallel with these developments, equally rapid progress has been made on research into new materials with very strong electron-electron interactions, which lead to high quasiparticle masses and an exciting variety of metallic, superconducting and magnetic ground states. For technical reasons the two fields have advanced in parallel, with little cross-fertilisation of ideas and techniques. The goal of this jointly supervised project is to combine the different expertise of our two groups to bring strongly interacting electrons into the mesoscopic regime. You will work both in St Andrews and at the spectacular new Harvard Nanoscience Center, performing pioneering experiments on the fabrication and measurement of correlated electron mesoscopic devices.
(Jointly affiliated to both University of St Andrews and Max Planck Institute for the Chemical Physics of Solids, Dresden)
Non-equilibrium and non-adiabatic effects in Bose-Einstein condensates
Hooley, Dr Chris - cah19@st-andrews.ac.uk
When a gas of bosonic atoms is cooled to very low temperatures, it undergoes a phase transition in which a macroscopic fraction of the atoms enters the lowest single-particle state of the system. This effect, called Bose-Einstein condensation, was predicted in 1924, but not directly observed until 1995 - the main difficulty being, of course, that gases don't tend to stay gaseous down to microkelvin temperatures unless cooled with great care! To this end, ingenious devices involving electromagnetic trapping and laser- and evaporative cooling have been devised. Recent experiments involve subjecting the atom cloud to laser standing waves (so-called "optical lattices") as well as the background trapping potential that stops the atoms from leaving the system. One of the most exciting opportunities presented by these set-ups is the opportunity to study quantum processes far from equilibrium: since the characteristic time-scales of the Bose gas are rather long, it's easy to make a "sudden" change in the laser field. Indeed, the study of such non-equilibrium effects is vital, as they are in fact the key to measuring the properties of such gases in the first place (via "time-of-flight" experiments). This theoretical project aims to put our understanding of non-equilibrium processes in trapped Bose- and Fermi gases on a firmer footing, addressing such issues as:
- atom-atom correlations during cloud expansion;
- anti-bound states from sudden quenching of the condensate;
- growth models for low-temperature Bose-Einstein fluids;
- measuring the BCS state for fermions.
Established relations with several experimental groups active in the field (e.g. the Inguscio group in Florence, the Hinds group at Imperial, and the Schmiedmayer group at Heidelberg) are expected to provide fruitful and up-to-date experimental information. The majority of the work will consist of pen-and-paper calculations, perhaps supplemented by some computational analysis.
When a gas of bosonic atoms is cooled to very low temperatures, it undergoes a phase transition in which a macroscopic fraction of the atoms enters the lowest single-particle state of the system. This effect, called Bose-Einstein condensation, was predicted in 1924, but not directly observed until 1995 - the main difficulty being, of course, that gases don't tend to stay gaseous down to microkelvin temperatures unless cooled with great care! To this end, ingenious devices involving electromagnetic trapping and laser- and evaporative cooling have been devised. Recent experiments involve subjecting the atom cloud to laser standing waves (so-called "optical lattices") as well as the background trapping potential that stops the atoms from leaving the system. One of the most exciting opportunities presented by these set-ups is the opportunity to study quantum processes far from equilibrium: since the characteristic time-scales of the Bose gas are rather long, it's easy to make a "sudden" change in the laser field. Indeed, the study of such non-equilibrium effects is vital, as they are in fact the key to measuring the properties of such gases in the first place (via "time-of-flight" experiments). This theoretical project aims to put our understanding of non-equilibrium processes in trapped Bose- and Fermi gases on a firmer footing, addressing such issues as:
- atom-atom correlations during cloud expansion;
- anti-bound states from sudden quenching of the condensate;
- growth models for low-temperature Bose-Einstein fluids;
- measuring the BCS state for fermions.
Established relations with several experimental groups active in the field (e.g. the Inguscio group in Florence, the Hinds group at Imperial, and the Schmiedmayer group at Heidelberg) are expected to provide fruitful and up-to-date experimental information. The majority of the work will consist of pen-and-paper calculations, perhaps supplemented by some computational analysis.
Nonequilibrium physics in many-body quantum optics systems
Keeling, Dr Jonathan - jmjk@st-andrews.ac.uk
The aim of this project is to explore phase transitions in non-equilibrium quantum systems, and in particular, those involving many body quantum optics that is readily accessible to current or future experiments with cold atoms or superconducting qubits.
The last few years have seen a growing range of experimental systems in which collective quantum optical effects can be studied, and which prompt important questions about the differences between "quantum" phase transitions in open and closed quantum systems, and whether open quantum systems can ever be described as displaying a quantum phase transition. In particular, experiments by the group of Esslinger in ETH have shown how cold atoms in an optical cavity subject to an external coherent pump can undergo a transition to a superradiant phase.
This project will consider related problems, in which different aspects of quantum phase transitions in non-equilibrium systems become accessible.
The aim of this project is to explore phase transitions in non-equilibrium quantum systems, and in particular, those involving many body quantum optics that is readily accessible to current or future experiments with cold atoms or superconducting qubits.
The last few years have seen a growing range of experimental systems in which collective quantum optical effects can be studied, and which prompt important questions about the differences between "quantum" phase transitions in open and closed quantum systems, and whether open quantum systems can ever be described as displaying a quantum phase transition. In particular, experiments by the group of Esslinger in ETH have shown how cold atoms in an optical cavity subject to an external coherent pump can undergo a transition to a superradiant phase.
This project will consider related problems, in which different aspects of quantum phase transitions in non-equilibrium systems become accessible.
Novel Quantum Order in Vector Magnetic Fields
Mackenzie, Prof Andy - apm9@st-andrews.ac.uk
Strongly interacting electron systems are one of the best hosts for study of the quantum many-body problem. Experimental discoveries made in the past decade show that, in the cleanest materials, a variety of subtle collective states form at low temperatures. Some of these are metallic but involve the development of a preferred direction, driven not by the crystal symmetry but by the electron-electron interactions themselves. To study anisotropic responses like these, careful experiments are necessary – they can easily be missed if the correct probes are not used. Many of the states discovered so far have a coupling to externally applied magnetic fields, so these fields can be used to ‘train’ the systems’ response functions. This has highlighted the need to develop better and better ‘vector magnets’ in which the field vector can be changed via computer-controlled energisation of multiple superconducting coils. On this project you will have access to world-leading instruments capable of generating 1, 1 and 9 tesla along the x, y and z axes. This will enable you to study transport and thermodynamic quantities that cannot be accessed in standard instruments. Using this unique instrumentation, you will have the chance to investigate a range of the most exciting new strongly correlated materials in a fast-moving field of modern research.
(Jointly affiliated to both University of St Andrews and Max Planck Institute for the Chemical Physics of Solids, Dresden)
Strongly interacting electron systems are one of the best hosts for study of the quantum many-body problem. Experimental discoveries made in the past decade show that, in the cleanest materials, a variety of subtle collective states form at low temperatures. Some of these are metallic but involve the development of a preferred direction, driven not by the crystal symmetry but by the electron-electron interactions themselves. To study anisotropic responses like these, careful experiments are necessary – they can easily be missed if the correct probes are not used. Many of the states discovered so far have a coupling to externally applied magnetic fields, so these fields can be used to ‘train’ the systems’ response functions. This has highlighted the need to develop better and better ‘vector magnets’ in which the field vector can be changed via computer-controlled energisation of multiple superconducting coils. On this project you will have access to world-leading instruments capable of generating 1, 1 and 9 tesla along the x, y and z axes. This will enable you to study transport and thermodynamic quantities that cannot be accessed in standard instruments. Using this unique instrumentation, you will have the chance to investigate a range of the most exciting new strongly correlated materials in a fast-moving field of modern research.
(Jointly affiliated to both University of St Andrews and Max Planck Institute for the Chemical Physics of Solids, Dresden)
Setup of a Combined STM/AFM for the Study of Layered Oxide Materials
Wahl, Dr Peter - gpw2@st-andrews.ac.uk
In this project, the setup of a new combined STM/AFM is envisioned. The study of correlated electron materials by spectroscopic imaging STM has become a valuable tool, especially to study excitations at low energies and in magnetic fields. Adding force detection has a number of advantages, besides obtaining an additional observable the force allows to independently define the tip-sample distance. The is particularly beneficial when studying poorly conducting or even insulating samples, such as e.g. oxide heterostructures, which are often capped by insulating layers.
Your part in this project will be to implement force detection in an existing STM head (for a description, see, e.g., Ref. 1) and make it work in a cryogenic environment. In parallel, the sample preparation to study layered oxide materials in STM will be established. The aim of the project is to investigate the properties of 2D electron gases at the interface in layered oxide heterostructures by tunneling spectroscopy. It has been shown in the past that in these heterostructures, electronic correlation effects can be taylored such that the interfacial electron gas becomes, e.g., superconducting or exhibits magnetic ordering [2]. Observation of the electronic states of the two-dimensional electron gas in tunneling spectroscopy would open the possibility to study the properties on the nanometer scale. The first part of this project will be carried out at the Max-Planck-Institute for Solid State Research, Stuttgart, Germany.
S.C. White, U.R. Singh and P. Wahl, A stiff STM head for measurement at low temperatures and in high magnetic fields, Rev. Sci. Instr. 82, 113708 (2011).
J. Mannhart and D. Schlom, Science 327, 1607 (2010).
In this project, the setup of a new combined STM/AFM is envisioned. The study of correlated electron materials by spectroscopic imaging STM has become a valuable tool, especially to study excitations at low energies and in magnetic fields. Adding force detection has a number of advantages, besides obtaining an additional observable the force allows to independently define the tip-sample distance. The is particularly beneficial when studying poorly conducting or even insulating samples, such as e.g. oxide heterostructures, which are often capped by insulating layers.
Your part in this project will be to implement force detection in an existing STM head (for a description, see, e.g., Ref. 1) and make it work in a cryogenic environment. In parallel, the sample preparation to study layered oxide materials in STM will be established. The aim of the project is to investigate the properties of 2D electron gases at the interface in layered oxide heterostructures by tunneling spectroscopy. It has been shown in the past that in these heterostructures, electronic correlation effects can be taylored such that the interfacial electron gas becomes, e.g., superconducting or exhibits magnetic ordering [2]. Observation of the electronic states of the two-dimensional electron gas in tunneling spectroscopy would open the possibility to study the properties on the nanometer scale. The first part of this project will be carried out at the Max-Planck-Institute for Solid State Research, Stuttgart, Germany.
S.C. White, U.R. Singh and P. Wahl, A stiff STM head for measurement at low temperatures and in high magnetic fields, Rev. Sci. Instr. 82, 113708 (2011).
J. Mannhart and D. Schlom, Science 327, 1607 (2010).
Spectroscopic studies of artificial quantum matter
King, Dr Phil - pdk6@st-andrews.ac.uk
Transition-metal oxides host a rich spectrum of properties such as high-temperature superconductivity, magnetism, and large responses to external stimuli, including colossal magnetoresistance and metal-insulator transitions. The ability to engineer such properties at will is an essential prerequisite for their use in advanced electronic applications, and would provide a unique playground for studying the quantum many-body problem. In this project, you will help to develop a novel system for the growth of custom oxide thin films by reactive molecular-beam epitaxy. This system will be coupled to a brand new angle-resolved photoemission (ARPES) facility at the UK synchrotron, Diamond Light Source, providing unprecedented opportunities to study the electronic structure and underlying many-body interactions of the films that you grow. You will tailor these properties using epitaxial strain, quantum confinement, and the creation of digital-oxide superlattices, with the ultimate goal to develop methodologies for the rational design of functional oxide materials.
This is an EPSRC CASE studentship offered in collaboration with Dr. Thorsten Hesjedal (Diamond Light Source & University of Oxford) and Dr. Moritz Hoesch (Diamond Light Source). You will spend extended periods developing and utilizing state-of-the-art facilities at the Rutherford Appleton Laboratory in Didcot, Oxfordshire, where Diamond is located.
Transition-metal oxides host a rich spectrum of properties such as high-temperature superconductivity, magnetism, and large responses to external stimuli, including colossal magnetoresistance and metal-insulator transitions. The ability to engineer such properties at will is an essential prerequisite for their use in advanced electronic applications, and would provide a unique playground for studying the quantum many-body problem. In this project, you will help to develop a novel system for the growth of custom oxide thin films by reactive molecular-beam epitaxy. This system will be coupled to a brand new angle-resolved photoemission (ARPES) facility at the UK synchrotron, Diamond Light Source, providing unprecedented opportunities to study the electronic structure and underlying many-body interactions of the films that you grow. You will tailor these properties using epitaxial strain, quantum confinement, and the creation of digital-oxide superlattices, with the ultimate goal to develop methodologies for the rational design of functional oxide materials.
This is an EPSRC CASE studentship offered in collaboration with Dr. Thorsten Hesjedal (Diamond Light Source & University of Oxford) and Dr. Moritz Hoesch (Diamond Light Source). You will spend extended periods developing and utilizing state-of-the-art facilities at the Rutherford Appleton Laboratory in Didcot, Oxfordshire, where Diamond is located.
Tailoring correlated solids through electrostatic surface control
King, Dr Phil - pdk6@st-andrews.ac.uk
Control of the source-drain conductivity of a semiconductor transistor by applying a small external voltage (so-called field-effect doping) underpins almost all current electronic devices. However, the transistor is widely accepted to be approaching its physical limits of performance. A new approach is required. In this project, you will investigate the potential of correlated electron materials – compounds where there are strong interactions between the constituent particles and which often exhibit emergent phases such as superconductivity and magnetism – for such applications. You will develop schemes to mimic field-effect doping in ultra-high vacuum while still leaving the sample surface accessible for advanced spectroscopic measurements. In particular, you will employ angle-resolved photoemission (ARPES) to simultaneously uncover how the electronic structure and many-body interactions evolve with such doping. ARPES measurements will be performed using our state-of-the-art system in St Andrews, as well as synchrotron light sources in the UK, Europe, and the USA.
Control of the source-drain conductivity of a semiconductor transistor by applying a small external voltage (so-called field-effect doping) underpins almost all current electronic devices. However, the transistor is widely accepted to be approaching its physical limits of performance. A new approach is required. In this project, you will investigate the potential of correlated electron materials – compounds where there are strong interactions between the constituent particles and which often exhibit emergent phases such as superconductivity and magnetism – for such applications. You will develop schemes to mimic field-effect doping in ultra-high vacuum while still leaving the sample surface accessible for advanced spectroscopic measurements. In particular, you will employ angle-resolved photoemission (ARPES) to simultaneously uncover how the electronic structure and many-body interactions evolve with such doping. ARPES measurements will be performed using our state-of-the-art system in St Andrews, as well as synchrotron light sources in the UK, Europe, and the USA.
Topological Superconductivity
Mackenzie, Prof Andy - apm9@st-andrews.ac.uk
The concepts of symmetry and symmetry breaking cut across all sub-fields of physics. Whether crystal symmetry in solids, gauge symmetry in superconductors or time reversal symmetry in ferromagnets, we have become used to defining phases of matter in terms of order parameters associated with symmetry breaking. However, not all collective quantum states can be fully characterised in terms of their symmetries. In some systems phases are classified in terms of their topological characteristics. Although this has been known for several decades, it was thought to apply in highly restricted circumstances. Exciting and rapid developments over the past five years have shown that these topologically characterised phases are likely to be much more widespread than first thought, and that, in the long term, it may be possible to exploit their properties in adventurous new technologies. Although progress has been rapid, fascinating theoretical questions remain, not least the interplay between symmetry and topology. The field is also ripe for experimental study. Superconductors are among the most fascinating candidates for topological systems. A host of intriguing theoretical proposals exist, but the extent to which they are observable in practice has yet to be determined. This project is concerned with investigating candidate topological superconductors, using a combination of the world-leading experimental facilities in St Andrews, Dresden and Cornell. The project is ambitious, and would be best suited to a candidate with both experimental and theoretical aptitude.
(Jointly affiliated to both University of St Andrews and Max Planck Institute for the Chemical Physics of Solids, Dresden)
The concepts of symmetry and symmetry breaking cut across all sub-fields of physics. Whether crystal symmetry in solids, gauge symmetry in superconductors or time reversal symmetry in ferromagnets, we have become used to defining phases of matter in terms of order parameters associated with symmetry breaking. However, not all collective quantum states can be fully characterised in terms of their symmetries. In some systems phases are classified in terms of their topological characteristics. Although this has been known for several decades, it was thought to apply in highly restricted circumstances. Exciting and rapid developments over the past five years have shown that these topologically characterised phases are likely to be much more widespread than first thought, and that, in the long term, it may be possible to exploit their properties in adventurous new technologies. Although progress has been rapid, fascinating theoretical questions remain, not least the interplay between symmetry and topology. The field is also ripe for experimental study. Superconductors are among the most fascinating candidates for topological systems. A host of intriguing theoretical proposals exist, but the extent to which they are observable in practice has yet to be determined. This project is concerned with investigating candidate topological superconductors, using a combination of the world-leading experimental facilities in St Andrews, Dresden and Cornell. The project is ambitious, and would be best suited to a candidate with both experimental and theoretical aptitude.
(Jointly affiliated to both University of St Andrews and Max Planck Institute for the Chemical Physics of Solids, Dresden)
Ultrafast Photophysics of Organic Semiconductors
Samuel, Prof Ifor - idws@st-andrews.ac.uk
This project will explore the physics of remarkable plastic-like semiconductors, such as light-emitting polymers. These materials are model one-dimensional systems and this strongly influences their physics – for example it means that excitons are strongly bound and that there is a substantial distortion of the material when it is excited. The purpose of this project is to study the nature of the excited states in these materials and how they evolve when the sample is excited by light. The initial rearrangement of the molecules occurs on a timescale of 100 femtoseconds. Remarkably we can make measurements on this timescale using advanced femtosecond lasers. We wish to explore how the excited states form and then decay, and how these processes relate to the structure of the material. The results will help understand light emission and amplification, and complementary theoretical work is underway at Heriot-Watt University by Prof. Ian Galbraith.
This project will explore the physics of remarkable plastic-like semiconductors, such as light-emitting polymers. These materials are model one-dimensional systems and this strongly influences their physics – for example it means that excitons are strongly bound and that there is a substantial distortion of the material when it is excited. The purpose of this project is to study the nature of the excited states in these materials and how they evolve when the sample is excited by light. The initial rearrangement of the molecules occurs on a timescale of 100 femtoseconds. Remarkably we can make measurements on this timescale using advanced femtosecond lasers. We wish to explore how the excited states form and then decay, and how these processes relate to the structure of the material. The results will help understand light emission and amplification, and complementary theoretical work is underway at Heriot-Watt University by Prof. Ian Galbraith.
