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

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 ${\mathcal{C}}^{\mathrm{res}}:{\mathcal{C}}^{\mathrm{rel}}=1:-\frac{1}{2}$. In this paper we develop the generic coupled block model to prove the slope ratio of sound velocity shift between two regimes is ${\mathcal{C}}^{\mathrm{res}}:{\mathcal{C}}^{\mathrm{rel}}=1:-1$ 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 ${\mathcal{C}}^{\mathrm{res}}:{\mathcal{C}}^{\mathrm{rel}}=-1:\frac{1}{2}$. In this paper we apply the electric dipole-dipole interaction, to prove that the slope ratio between two regimes is ${\mathcal{C}}^{\mathrm{res}}:{\mathcal{C}}^{\mathrm{rel}}=-1:1$ 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.

41 pages, 10 pictures