Microwave-absorption-induced heating of surface state electrons on liquid ³He

A resonance-induced change is observed in the resistivity of surface state electrons (SSEs) exposed to microwave (MW) radiation. The MW frequency corresponds to the transition energy between the two lowest Rydberg energy levels. All measurements are performed with electrons on liquid ³He in the temperature range 0.45-0.65K in which the electron relaxation time and the MW absorption linewidth are determined by the collisions of the electrons with helium vapor atoms. The resistivity is found to increase in the vicinity of the MW resonance at all values of the input MW power which is varied by two orders of magnitude. This effect is attributed to the heating of SSEs by the resonance MW radiation. The temperature and the momentum relaxation rate of the hot electrons are calculated as a function of the MW power in the cell, and the Rabi frequency is determined from a comparison of the theoretical result with the experiment. In addition, the broadening of the absorption signal caused by the heating is studied experimentally, and the results are found to be in good agreement with our calculations.