Abstract

Electrons in equilibrium occupy states according to the Fermi-Dirac distribution whose discontinuous jump defines their Fermi surface. But how should electrons occupy states when they are driven far from equilibrium by shining coherent light on them? would their occupation still have a sharp jump? or would their fermi surfaces be simply smeared out by heating effects?

Our recent investigations have revealed that electrons under coherent monochromatic illumination develop emergent non-equilibrium fermi surfaces. For example, when tunneling into a fermion bath (i.e. a metallic back gate), the non-equilibrium occupation has a staircase shape with extra jumps, and therefore new emergent Fermi surfaces. And, remarkably, when in contact with boson baths (i.e. phonons), the non-equilibrium steady state has multiple sharp kinks and resembles a non-Fermi liquid state. These kink-Fermi surfaces remain sharp even when the bath is at finite temperature, a phenomenon with no analogue in equilibrium Fermi and non-Fermi liquids. These novel non-equilibrium Fermi surfaces allow for a more fundamental re-interpretation of MIRO (microwave-induced-resistance-oscillations) phenomena in 2DEGs, and provide a novel and promising blueprint for the realization of true non-equilibrium Floquet steady states in two-dimensional materials under low frequency radiations.