A Microscopic Field Theory for the Universal Shift of Sound Velocity and Dielectric Constant in Low-Temperature Glasses

TL;DR

This paper develops a microscopic field theory to explain the universal logarithmic temperature dependence of sound velocity and dielectric constant shifts in low-temperature glasses, resolving discrepancies with previous models and aligning with experimental data.

Contribution

It introduces a coupled block model and real space renormalization technique to accurately predict the slope ratios of sound velocity and dielectric constant shifts, emphasizing the role of long-range interactions.

Findings

The slope ratio of sound velocity shift is 1:-1, matching most measurements.

The dielectric constant shift slope ratio is -1:1, consistent with experiments.

Universal properties originate from 1/r^3 long-range interactions, independent of microscopic details.

Abstract

In low-temperature glasses, the sound velocity changes as the logarithmic function of temperature below $10$K: $[c(T) - c(T_0)]/c(T_0) = \mathcal{C}\ln(T/T_0)$. With increasing temperature starting from $T=0$K, the sound velocity does not increase monotonically, but reaches a maximum at a few Kelvin and decreases at higher temperatures. Tunneling-two-level-system (TTLS) model explained the $\ln T$ dependence of sound velocity shift. In TTLS model the slope ratio of $\ln T$ dependence of sound velocity shift between lower temperature increasing regime (resonance regime) and higher temperature decreasing regime (relaxation regime) is $\mathcal{C}^{\rm res }:\mathcal{C}^{\rm rel }=1:-\frac{1}{2}$. In this paper we develop the generic coupled block model to prove the slope ratio of sound velocity shift between two regimes is $\mathcal{C}^{\rm res }:\mathcal{C}^{\rm rel }=1:-1$ rather than $1:-\frac{1}{2}$, which agrees with the majority of the measurements. The dielectric constant shift in low-temperature glasses, $[\epsilon_r(T)-\epsilon_r(T_0)]/\epsilon_r(T_0)$, has a similar logarithmic temperature dependence below $10$K: $[\epsilon(T)-\epsilon(T_0)]/\epsilon(T_0) = \mathcal{C}\ln(T/T_0)$. In TTLS model the slope ratio of dielectric constant shift between resonance and relaxation regimes is $\mathcal{C}^{\rm res}:\mathcal{C}^{\rm rel}=-1:\frac{1}{2}$. In this paper we apply the electric dipole-dipole interaction, to prove that the slope ratio between two regimes is $\mathcal{C}^{\rm res}:\mathcal{C}^{\rm rel} = -1:1$ rather than $-1:\frac{1}{2}$. Our result agrees with the dielectric constant measurements. By developing a real space renormalization technique for glass non-elastic and dielectric susceptibilities, we show that these universal properties essentially come from the $1/r^3$ long range interactions, independent of the materials' microscopic properties.