Resonance Microwave Absorption in He II.

TL;DR

This study investigates microwave absorption in superfluid helium-4 at 40-200 GHz, revealing resonance at 180.3 GHz linked to roton excitations, with temperature-dependent behavior and hysteresis near the lambda point.

Contribution

It demonstrates microwave resonance absorption linked to roton creation in superfluid helium-4 and correlates it with the temperature-dependent roton gap.

Findings

Resonance absorption detected at 180.3 GHz.

Resonance frequency decreases with temperature.

Hysteretic behavior observed near the lambda point.

Abstract

Microwave (MW) absorption in liquid 4He is investigated in the frequency range of 40-200 GHz at T = 1.4 - 2.5 K. Whispering gallery of waves was generated by a dielectric disc resonator immersed into the liquid. Resonance absorption of MWs was detected at 180.3 GHz, which corresponds to the roton minimum of the liquid helium excitation spectrum. The creation of a single roton is possible because of the presence of the resonator wall which absorbs an extra momentum. The resonance frequency is shown to decreases with temperature in an excellent agreement with the temperature dependence of the roton gap obtained previously in the neutron scattering experiment. The temperature dependence of the MW absorption data indicates the anomalous behavior near the lambda-point and displays the hysteretic character.