Open positions

Currently, we have the following PhD projects available:

PhD project: Electrically driven polariton devices

Exciton-polaritons are mixed bosonic quasiparticles that form when excitons and photons strongly interact inducing a steady energy exchange between both types of particles. Polaritons are usually created in semiconductor microcavities providing quantum confined excitons in active quantum well layers and photonic confinement by sandwiching those active layers between top and bottom Bragg mirrors. In contrast to conventional semiconductor lasers that rely on the stimulated emission of photons, polariton lasers undergo stimulated scattering promising ultra-low threshold generation of coherent light by the macroscopic occupation of the bosonic polariton ground state. This process does not require population inversion as it is the basic requirement for the operation of a conventional laser. The evidence for room-temperature polariton condensation in optically pumped polariton microcavities [1] besides the recent first demonstration of an electrically driven polariton laser [2] establish the young scientific branch of 'polaritonics' as a serious option besides 'photonics'.
This project aims at pushing electrically driven polariton light emitting devices to their maximum performance. This includes the unambiguous evidence for electrically induced polariton condensation without applying an external magnetic field as well as reducing the condensation threshold and figures of merit for condensation. The latter requires an improvement of both the current injection and polariton stability by optimization of the microcavity geometry and morphology.

[1] S Christopoulos et al, Phys Rev Lett 98, 126405 (2007)
[2] C Schneider et al, Nature 497, 348 (2013)

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PhD project: Polariton condensation in microcavity lattices

In 1928, Paul Dirac brilliantly derived a theory combining relativity and quantum mechanics by describing the relativistic motion of electrons with a massless linear dispersion relation. This recently gave great insight into the formation of Dirac fermions in condensed matter systems like graphene, carbon nanotubes or topological insulators by the observation of unique transport properties such as the anomalous quantum Hall effect or Klein tunneling. An outstanding platform to create and investigate bosonic Dirac-like particles and mimic the relativistic properties of real Dirac particles is given by the two-dimensional arrangement of polaritons in microcavity lattices. These two-dimensional polariton lattices create higher orbitals in the polariton band structure allowing the crossing of two degenerate polariton bands (Dirac points). Several lattice geometries such as honeycomb or triangular lattices have already been proposed for the formation of such Dirac points. The triangular lattice has already experimentally been proven to show Dirac bosons in higher order bands [1] therewith laying the ground for exciting more research.

[1] N Y Kim et al, New J Phys 15, 035032 (2013)

(PDF version)

PhD project: Bose-Einstein condensation of organic polaritons at room temperature

Light-matter interaction is a field of tremendous interest. In the strong coupling regime between a layer of active material hosting bound electron-hole-pairs (called 'excitons') and a microcavity, new quasi-particles emerge called polaritons. These polaritons have fascinating properties. Due to their ultra-light effective mass and their bosonic nature, they can undergo Bose-Einstein condensation at elevated temperatures. In contrast to polaritons in the in-organic semiconductor GaAs, organic solids can have excitons binding energies of up to a few hundred meV. This makes them ideally suited for the observation of room-temperature polariton lasing and Bose-Einstein-Condensation [1,2].
This project is about the investigation of organic polaritons and their condensation properties. In the first part of the project, the focus will be on the fabrication of coupled organic-cavity structures in collaboration with the Organic Semiconductor Centre. You will design, realise and characterise organic polariton samples that serve you for spectroscopic investigations like angularly resolved imaging as well as temporal and spatial correlation measurements. This will enable you to observe Bose-Einstein-Condensation of organic polaritons at room-temperature.

[1] S Kéna-Cohen & S R Forrest, Nat. Phot. 4, 371 (2010)
[2] D Plumhof et al, Nat. Mat., DOI: 10.1038/NMAT3825 (2013)

(PDF version)

PhD project: Semiconductor Integrated Quantum Photonics

Quantum information processing is a rapidly developing research field. Exploiting quantum bits instead of classical bits, offers key advantages for future technologies such as secure communication and ultra-fast computation. While breakthrough lab-size experiments have proven the validity of these quantum technology concepts, any wide spread utilization will require dense integration of functionalities. Semiconductor integrated quantum photonic circuits with on-chip single photon sources [1] and detectors [2] are a very promising route for full on-chip integration. Utilizing photonic crystals, structures with periodic variations of refractive indices, enable the guiding of the emission and propagation of photons. Single quantum dots embedded in photonic crystals are efficient single photon sources. After traveling along a waveguide, these single photons can be detected by on-chip auto-correlators [3], based on superconducting single photon detectors to probe quantum correlations. Such building blocks are key components of a quantum information processing platform.

[1] T B Hoang et al, Appl Phys Lett 100, 061122 (2012)
[2] J P Sprengers et al, Appl Phys Lett 99, 181110 (2011)
[3] D Sahin et al, Opt Express 21, 11162 (2013)

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If you are interested in one of the above listed projects, please contact
Sven Höfling (sh222@st-andrews.ac.uk) or Christof P Dietrich (cpd3@st-andrews.ac.uk)