Microwave-Absorption-Induced Heating of Surface State Electrons on Liquid 3He

TL;DR

This study demonstrates that microwave radiation resonant with surface state electrons on liquid helium causes electron heating, increasing resistivity, with detailed analysis of relaxation rates, linewidth broadening, and Rabi frequency.

Contribution

It provides the first detailed experimental and theoretical analysis of microwave-induced heating effects on surface state electrons on liquid helium at ultra-low temperatures.

Findings

Resistivity increases with microwave power due to electron heating.

Theoretical calculations match experimental linewidth broadening.

Rabi frequency and relaxation rates are quantitatively determined.

Abstract

A resonance-induced change in the resistivity of the surface state electrons (SSE) exposed to the microwave (MW) radiation is observed. The MW frequency corresponds to the transition energy between two lowest Rydberg energy levels. All measurements are done with electrons over liquid 3He in a temperature range 0.45-0.65 K, in which the electron relaxation time and the MW absorption linewidth are determined by collisions with helium vapor atoms. The input MW power is varied by two orders of magnitude, and the resistivity is always found to increase. This effect is attributed to the heating of electrons with 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 the 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.