Relaxation of the Excited Rydberg States of Surface Electrons on Liquid Helium

TL;DR

This study directly observes the decay of excited Rydberg states of surface electrons on liquid helium, revealing relaxation mechanisms and dynamics influenced by inelastic scattering, with the longest relaxation time around 1 microsecond at very low temperatures.

Contribution

First direct measurement of excited-state decay in surface electrons on liquid helium, linking relaxation dynamics to inelastic scattering mechanisms through experimental and theoretical analysis.

Findings

Relaxation time up to 1 microsecond at 135 mK.

Dominant decay via two-ripplon emission.

Population dynamics influenced by multisubband structure.

Abstract

We report the first direct observation of the decay of the excited-state population in electrons trapped on the surface of liquid helium. The relaxation dynamics, which are governed by inelastic scattering processes in the system, are probed by the real-time response of the electrons to a pulsed microwave excitation. Comparison with theoretical calculations allows us to establish the dominant mechanisms of inelastic scattering for different temperatures. The longest measured relaxation time is around 1 us at the lowest temperature of 135 mK, which is determined by the inelastic scattering due to the spontaneous two-ripplon emission process. Furthermore, the image-charge response shortly after applying microwave radiation reveals interesting population dynamics due to the multisubband structure of the system.