Can Warmer than Room Temperature Electrons Levitate Above a Liquid Helium Surface?

Abstract

We address the problem of overheating of electrons trapped on the liquid helium surface by cyclotron resonance excitation. Previous experiments, suggest that electrons can be heated to temperatures up to 1000K more than three order of magnitude higher than the temperature of the helium bath in the sub-Kelvin range. In this work we attempt to discriminate between a redistribution of thermal origin and other out-of equilibrium mechanisms that would not require so high temperatures like resonant photo-galvanic effects, or negative mobilities. We argue that for a heating scenario the direction of the electron flow under cyclotron resonance can be controlled by the shape of the initial electron density profile, with a dependence that can be modeled accurately within the Poisson-Boltzmann theory framework. This provides an self consistency-check to probe if the redistribution is indeed consistent with a thermal origin. We find that while our experimental results are consistent with the Poisson-Boltzmann theoretical dependence but some deviations suggest that other physical mechanisms can also provide a measurable contribution. Analyzing our results with the heating model we find that the electron temperatures increases with electron density under the same microwave irradiation conditions. This unexpected density dependence calls for a microscopic treatment of the energy relaxation of overheated electrons. arXiv:1807.09501v1 [cond-mat.mes-hall]

Coupled pair of one- and two-dimensional magnetoplasmons on electrons on helium

“…The position of magnetoplasmon resonances then shows as peaks in the admittance Y ( f ac ) for a fixed bias voltage V b . This bias between the outer guard and central electrodes can tune the frequency of the magnetoplasmons by controlling the shape of the electron cloud [33,37]. For V b < 0 the electron cloud adopts a "plateau" density profile, where the density n 0 (r) is a monotonously decaying function of the radial distance to the cloud center r, while for V b > 0 the electron density takes a "caldera" profile which has a density maximum inside the guard region at the edge of the electron cloud [Fig.…”

Coupled pair of one and two dimensional magneto-plasmons on electrons on helium

“…The position of magnetoplasmon resonances then shows as peaks in the admittance Y (f ac ) for a fixed bias voltage V b . This bias between the outer guard and central electrodes can tune the frequency of the magneto-plasmons by controlling the shape of the electron cloud [32,35]. For V b < 0 the electron cloud adopts a "plateau" density profile, where the density n 0 (r) is a monotonously decaying function of the radial distance to the cloud center r, while for V b > 0 the electron density takes a "caldera" profile which has a density maximum inside the guard region at edge of the electron cloud (Fig.…”