Resonant Photovoltaic Effect in Surface-State Electrons on Liquid Helium
  We observed an ultra-strong photovoltaic effect induced by resonant intersubband absorption of microwaves in a two-dimensional electrons system on the surface of liquid helium. The effect emerges in the regime of microwave-induced vanishing of dissipative conductance reported previously [D. Konstantinov and K. Kono: Phys. Rev. Lett. 105 (2010) 226801)] and is characterized by a nonequilibrium spatial distribution of electrons in the confining electrostatic potential. The electrostatic energy acquired by an electron exceeds other relevant energies by several orders of magnitude. 
Denis Konstantinov, A. D. Chepelianskii, Kimitoshi Kono
cond-mat.mes-hall