Generation of electromagnetic radiation by a heat flow in He II

TL;DR

This paper reports the experimental detection of electromagnetic radiation generated by heat flow in superfluid helium, revealing a new effect linked to the roton energy gap and demonstrating He II's two-level system behavior.

Contribution

The study provides the first experimental evidence of electromagnetic radiation generated by heat flow in superfluid helium and links it to roton energy dynamics.

Findings

Electromagnetic radiation detected in the 1.4-2.17K range.

Radiation frequency around 180GHz decreasing with temperature.

He II acts as a two-level system related to roton energy.

Abstract

A new effect of electromagnetic radiation generated by heat flow in superfluid helium has been detected experimentally. The generating heat flow was produced using hydrodynamic thermal guns. Electromagnetic radiation was registered with a dielectric disk resonator in the interval 1.4-2.17K. The power of the thermal gun heater varied within Q up to 1mW. A distinct signal of electromagnetic radiation was registered when the thermal gun was on and there was no signal at Q=0. The frequency of the generated electromagnetic radiation was measured with a Fabry-Perrot interferometer. It was about 180GHz at T=1.4K and decreased with a rising temperature practically following the temperature dependence of a roton gap. The detected signal was investigated as a function of the heat flow temperature, direction and power Q. The results obtained show that He II behaves as a two - level system in which the difference between the levels is equal to the roton energy.