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, sigma(xx) -> 0, 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.