Observation of second sound in a rapidly varying temperature field in Ge

TL;DR

This study demonstrates the observation of second sound in germanium across a wide temperature range by using a rapidly varying temperature field, revealing new possibilities for wave-like heat transport in various materials.

Contribution

It introduces a novel method to observe second sound in materials over broad temperature ranges using high-frequency thermal excitation.

Findings

Second sound observed in Ge from 7 K to room temperature.

Phase lag analysis reveals heat wave propagation characteristics.

Potential to control heat via oscillatory thermal methods.

Abstract

Second sound is known as the thermal transport regime where heat is carried by temperature waves. Its experimental observation was previously restricted to a small number of materials, usually in rather narrow temperature windows. We show that it is possible to overcome these limitations by driving the system with a rapidly varying temperature field. This effect is demonstrated in bulk Ge between 7 kelvin and room temperature, studying the phase lag of the thermal response under a harmonic high frequency external thermal excitation, addressing the relaxation time and the propagation velocity of the heat waves. These results provide a new route to investigate the potential of wave-like heat transport in almost any material, opening opportunities to control heat through its oscillatory nature.