PhD Opportunities

We are looking for ambitious students interested in pursuing a career in modern condensed matter physics. Current projects are listed below.

1. Laser based ARPES from ultra-pure correlated electron systems

Solids with strong electronic correlations often host intriguing collective states with potentially useful  properties. Standard experimental probes can readily  characterize the thermodynamic and transport signatures  of these quantum many body states but give little information about the underlying microscopic electronic structure. Angle resolved photoemission (ARPES) is a uniquely powerful spectroscopic technique that directly maps the energy – momentum distribution of the interacting electronic states, which govern the macroscopic properties of correlated electron systems. In this project, you will push the current state-of-the-art in ARPES by employing an intense deep-UV laser as a new excitation source for very high-resolution electron spectroscopy. The laser-ARPES experiments will focus on the Ruddlesden-Popper series Srn+1RunO3n+1 of ultraclean, layered ruthenium oxides. This family of materials exhibits a spectacular range of poorly understood complex phases including spin-triplet super- conductivity, metamagnetism, density-waves or Mott-insulating states.

2. Spectroscopic STM studies of ferrous superconductors

The recent discovery of high-temperature superconductivity in iron-based compounds challenges our understanding of interacting electrons systems. In this project you will investigate the intriguing electronic properties of ferrous superconductors using spectroscopic imaging scanning tunneling microscopy. To this end, you will first setup and test a new low- temperature (< 1 K) STM, which is currently being designed. Once fully operational in early 2011, you will focus on the ‘11’ family of iron-chalcogenides Fe(Se/Te) and investigate their electronic structure by imaging the interference pattern of wave-like quasiparticle excitations. These experiments will be performed in close collaboration with other group members working on complementary angle resolved photoemission (ARPES) studies on the same samples and promise unique insight into a family of materials with fascinating properties. 

3. Spin helical Surface States on Topological Insulators

It had been assumed since the 1930’s that ‘band insulators’ - materials in which an energy gap is created by the periodic potential of the ion cores - were fully understood. Only thanks to very recent theoretical work motivated by the physics of graphene, it became clear that these materials fall into two distinct classes: conventional band insulators and an exciting new form dubbed ‘topological insulators’ characterized by the existence of metallic surface states with a Dirac dispersion and helical spin-structure. The highly unusual properties of these surface states, such as their unconventional spin texture and predicted protection from backscattering, render topological insulators interesting for novel applications in spintronics or magnetoelectric devices. Moreover, there are exciting proposals to utilize the special properties of topological surface states for novel schemes in quantum computing.
In this project you will study the Dirac dispersion of topological surface states directly using angle-resolved photoemission (ARPES). The experiments will be performed in our state-of-the-art spectroscopy lab at the University of St Andrews as well as at synchrotron light sources in Europe and the US, and will include the preparation and study of magnetic or superconducting thin films on surfaces of topological insulators.

4. Nanoscale Inhomogeneity of Correlated Materials from Spatially Resolved ARPES

Electronic inhomogeneity and phase separation on the nanometer to micrometer length scale is ubiquitous in correlated electron systems and is generally accepted to have a defining influence on many macroscopic properties. However, progress in understanding phase separation or in exploiting it in designer materials has been limited by the profound experimental challenges and by the difficulty in modeling such systems alike. Nano-ARPES, a novel technique combining the energy and momentum resolution of angle-resolved photoemission with sub-100 nm spatial resolution holds the promise to meet this challenge. In this project you will be involved in the development of a laser-based spatially resolved ARPES system at the university of St Andrews and you will use the most-advanced nano-focus synchrotron beamlines worldwide (currently at Elettra, Italy and Soleil, Paris, in the future also at Diamond, UK) for photoemission experiments on topical materials. First experiments will be on Mn-doped Sr3Ru2O7 and the Ru/Sr2RuO4 eutectic, for which some form of local inhomogeneity is already established.

Our typical funding sources make it easier to support UK and EU students, but exceptional students from overseas (USA, China, India etc.) are also encouraged to apply. Most notably, they can apply for support via SUPA with a deadline at the end of January, or SORSAS with a deadline in March.

For information please contact Felix Baumberger.