Acoustic Properties of Amorphous Solids at Very Low Temperatures: The Quest for Interacting Tunneling States

TL;DR

This paper investigates how strain affects the acoustic properties of amorphous metals at very low temperatures, providing evidence for interacting tunneling systems and emphasizing the importance of strain dependence in understanding these properties.

Contribution

It demonstrates the strain dependence of acoustic properties in amorphous metals and confirms the interaction between tunneling systems aligns with theoretical models.

Findings

Identifies a crossover related to strain energy and interaction energy.

Provides quantitative agreement with theoretical expectations.

Highlights the significance of strain dependence in low-temperature acoustic measurements.

Abstract

We discuss the strain dependence of the acoustic properties of amorphous metals in both normal and superconducting states, in the temperature range 0.1 mK $ \le T \le 1 $K. A crossover is found when the strain energy is of the order of the effective interaction energy between tunneling systems at the corresponding temperature. Our results provide clear evidence for the interaction between tunneling systems, whose energy is in quantitative agreement with theoretical expectations, and reveal that without the knowledge of the corresponding strain dependences, the measured temperature dependences below $\sim 50 $mK of the acoustic properties of disordered solids are rather meaningless.