CMSP Seminar Series - Stasi Seminar Room Leonardo on Thursday 31 January 11 am - Sebastian DIEHL

[CM Section]

Condensed Matter and Statistical Physics Seminar Series

Thursday 31 January at 11:00 a.m.
Luigi Stasi Seminar Room, first floor, Leonardo building

Sebastian DIEHL
University of Cologne, Germany

'Phase Transitions under Drive'

Abstract:
What is the nature of phase transitions in driven quantum systems?
We address this question in two opposite regimes, a rapidly periodically
driven Floquet system coupled to a bath and a slowly driven one, within
a non-equilibrium renormalization group approach.
In the periodically driven case, the infinitely rapidly driven limit
exhibits a second order phase transition analogous to a multi-mode
laser. However, we reveal that fluctuations turn the transition first
order when the driving frequency is finite. This can be traced back to a
universal mechanism, which crucially hinges on the competition of
degenerate, near critical modes associated to higher Floquet Brillouin
zones, in some analogy to the Halperin-Lubensky-Ma or Coleman-Weinberg
mechanism. A physical picture is that of a fluctuation induced many-body
Kapitza pendulum. The critical exponents of the infinitely rapidly
driven system -- including a new, independent one -- can yet be probed
experimentally upon smoothly tuning towards that limit.
The opposite, slowly driven limit, is governed by the Kibble-Zurek
mechanism of diabatic freeze out of the divergence of the correlation
length. Recasting this problem in a systematic RG formulation, we show
that the slow drive can be used to resolve not only the leading critical
exponents of the underlying equilibrium problem, but the full critical
exponent spectrum.