Inti Sodemann

The investigation of Fermi liquids has remained largely confined to the framework of equilibrium states of matter. But what is the fate of Fermi liquids and their Fermi surfaces when they are driven far away from equilibrium by strong time-dependent perturbations?

I will show that in a system of fermions driven by an oscillating electric field, the fermi Dirac occupation is replaced by a non-equilibrium "Fermi-Dirac Staircase"  displaying multiple discontinuous jumps in the occupations. This leads to the appearance of a "Matryoshka Fermi Liquid" state which possesses a collection of Fermi surfaces enclosed inside each other, resembling matryoshka dolls.

I will show how the Matryoshka Fermi Liquid allows to solve an old controversy in the field of optoelectronics, by proving that it is possible to have finite photo-currents even when light absorption is vanishingly small because the frequency lies within the optical gap of the metal. 

I will also show Matryoshka Fermi Liquid can shed new light on the understanding of MIRO (microwave induced resistance oscillations) phenomena, by demonstrating that when a magnetic field is applied to the Matryoshka Fermi Liquid, the different areas of the Matryoshka Fermi Surfaces lead to a pattern of low frequency modulations of the quantum oscillations controlled by the frequency of the AC drive.