Interacting quantum rotors in oxygen-doped germanium

TL;DR

This paper models the interactions of oxygen impurities in germanium as quantum rotors, predicting anomalous low-temperature behaviors such as power-law specific heats and dielectric susceptibility humps due to dipolar interactions.

Contribution

It introduces a quantum rotor model to explain low-temperature anomalies in oxygen-doped germanium caused by impurity interactions, a novel theoretical approach.

Findings

Power-law specific heats below 0.1 K in Ge:O

A hump in dielectric susceptibilities around 1 K

Interpretation based on local double-well potentials

Abstract

We investigate the interaction effect between oxygen impurities in crystalline germanium on the basis of a quantum rotor model. The dipolar interaction of nearby oxygen impurities engenders non-trivial low-lying excitations, giving rise to anomalous behaviors for oxygen-doped germanium (Ge:O) below a few degrees Kelvin. In particular, it is theoretically predicted that Ge:O samples with oxygen-concentration of 10$^{17-18}$cm$^{-3}$ show (i) power-law specific heats below 0.1 K, and (ii) a peculiar hump in dielectric susceptibilities around 1 K. We present an interpretation for the power-law specific heats, which is based on the picture of local double-well potentials randomly distributed in Ge:O samples.