Seminarium Fizyki Ciała Stałego

Over the past 15 years, exciton-polaritons in semiconductor microcavities have been well established as a new class of quantum fluids, with defining phenomena such as Bose-Einstein condensation and superfluidity, and characterized by a driven-dissipative situation which includes some partial equilibration during the particles lifetime. This exotic thermodynamical situation, lies somewhere between laser and ultracold atom physics, and as a result raises profund questions on the very nature of the phenomenon in terms of its universality class.

In order to add even more confusion to this question, we determined that phonons at elevated temperatures (T=[150K-250K]) can be used to warm up a polariton condensate in a tunable and controlled way, and with a thermal power output large enough to beat the single particle loss rate. We demonstrate with this method that a polariton condensate can be tuned continuously from a regime dominated by drive and dissipation (w=0), to a regime in which thermal fluctuations contribute as much (w=1) and even more (w=2.3) to the phenomenon. We find that for increasing w, the condensate properties acquire reminiscence from both regimes: a condensate thermal depletion channel opens up, the first-order correlation length shrinks, and the driven-dissipative vortices get disconnected by the thermal fluctuations.

From the thermodynamical point-of-view, this "halfway" regime (w~1) is unique, as it is connected to two different phenomena, each belonging to a different universality class, in a way which is to be clarified in future theoretical works.