Bistability and Hysteresis of Intersubband Absorption in Strongly Interacting Electrons on Liquid Helium

TL;DR

This paper investigates nonlinear microwave absorption in electrons on liquid helium, revealing how electron overheating and Coulomb interactions lead to bistability and hysteresis in the absorption response.

Contribution

It presents a theoretical and experimental analysis of how electron interactions and heating cause nonlinear effects like bistability and hysteresis in intersubband absorption.

Findings

Resonant absorption causes electron overheating and higher subband population.

Frequency shifts depend on electron temperature and interactions.

Hysteresis observed in absorption response during frequency modulation.

Abstract

We study nonlinear inter-subband microwave absorption of electrons bound to the liquid helium surface. Already for a comparatively low radiation intensity, resonant absorption due to transitions between the two lowest subbands is accompanied by electron overheating. The overheating results in a significant population of higher subbands. The Coulomb interaction between electrons causes a shift of the resonant frequency, which depends on the population of the excited states and thus on the electron temperature $T_e$. The latter is determined experimentally from the electron photoconductivity. The experimentally established relationship between the frequency shift and $T_e$ is in reasonable agreement with the theory. The dependence of the shift on the radiation intensity introduces nonlinearity into the rate of the inter-subband absorption resulting in bistability and hysteresis of the resonant response. The hysteresis of the response explains the behavior in the regime of frequency modulation, which we observe for electrons on liquid $^3$He and which was previously seen for electrons on liquid $^4$He.