Superfluidity and the Berezinskii-Kosterlitz-Thouless phase in polariton condensates

Project level: PhD, Masters, Honours, Summer

Polariton condensates occur in two-dimensional semiconductor microcavities pumped by a laser.  The light excites electrons from the valence band to the conduction band, and the hole can then bind with the electron to form an exciton.  If these are strongly coupled to the mode of the cavity, the resulting quasiparticle is a boson called a polariton, and these have a mass about five orders of magnitude smaller than an electron.  This means that condensation of these bosons can occur at cryogenic temperatures.  

One of the features of polariton condensates is that the particles are continuously injected into the system, and they subsequently decay with a lifetime of around about 5 picoseconds.  This means that a polariton condensate forms are a driven-damped system out of thermal equilibrium – and so the nature of superfluidity in this situation is still not entirely clear.  This project will simulate 2D systems using the stochastic Gross-Pitaevskii equation, and try to understand the similarities and differences of the BKT superfluid phase in thermal equilibrium.