Acoustic properties of metallic glasses at low temperatures -- tunneling systems and their dephasing

TL;DR

This study investigates the low-temperature acoustic behavior of metallic glasses, testing the standard tunneling model and revealing that electron interactions significantly affect tunneling system coherence and dephasing.

Contribution

It provides new experimental data across multiple frequencies confirming previous findings and highlights the importance of line width considerations and electron interactions in tunneling models.

Findings

Experimental results largely confirm previous measurements.

Discrepancies with theory can be explained by line width effects.

Electron interactions can cause dephasing and destroy tunneling coherence.

Abstract

The low temperature acoustic properties of bulk metallic glasses measured over a broad range of frequencies rigorously test the predictions of the standard tunneling model. The strength of these experiments and their analyses is mainly based on the interaction of the tunneling states with conduction electrons or quasiparticles in the superconducting state. A new series of experiments at kHz and GHz frequencies on the same sample material essentially confirms previous measurements and their discrepancies with theoretical predictions. These discrepancies can be lifted by considering more correctly the line widths of the dominating two-level atomic-tunneling systems. In fact, dephasing caused or mediated by interaction with conduction electrons may lead to particularly large line widths and destroy the tunneling sytems' two-level character in the normal conducting state.