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

Beardo A.;Lopez-Suarez M.;Perez L. A.;Sendra L.;Alonso M. I.;Melis C.

Investigation

;Bafaluy J.;Camacho J.;Colombo L.

Conceptualization

;Rurali R.;Alvarez F. X.;Reparaz J. S.

2021-01-01

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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. High-frequency second sound is demonstrated in bulk natural Ge between 7 K and room temperature by studying the phase lag of the thermal response under a harmonic high-frequency external thermal excitation and addressing the relaxation time and the propagation velocity of the heat waves. These results provide a route to investigate the potential of wave-like heat transport in almost any material, opening opportunities to control heat through its oscillatory nature.