Dielectric Susceptibility and Heat Capacity of Ultra-Cold Glasses in Magnetic Field

TL;DR

This paper develops a theoretical model to explain the magnetic field dependence of dielectric susceptibility and heat capacity in ultra-cold glasses, highlighting the role of nuclear quadrupoles and angular momentum at low temperatures.

Contribution

It introduces a new theory coupling tunnelling motion to nuclear quadrupoles and angular momentum to explain magnetic effects in glasses at low temperatures.

Findings

Susceptibility increases as B^2 at weak fields and as 1/B at strong fields.

Heat capacity shows a Schottky peak due to angular momentum.

Nuclear quadrupoles contribute a B^2 dependence to heat capacity.

Abstract

Recent experiments demonstrated unexpected, even intriguing properties of certain glassy materials in magnetic field at low temperatures. We have studied the magnetic field dependence of the static dielectric susceptibility and the heat capacity of glasses at low temperatures. We present a theory in which we consider the coupling of the tunnelling motion to nuclear quadrupoles in order to evaluate the static dielectric susceptibility. In the limit of weak magnetic field we find the resonant part of the susceptibility increasing like $B^2$ while for the large magnetic field it behaves as 1/B. In the same manner we consider the coupling of the tunnelling motion to nuclear quadrupoles and angular momentum of tunnelling particles in order to find the heat capacity. Our results show the Schotky peak for the angular momentum part, and $B^2$ dependence for nuclear quadrupoles part of heat capacity, respectively. We discuss whether or not this approach can provide a suitable explanation for such magnetic properties.