Dielectric susceptibility and heat capacity of ultra-cold glasses in magnetic fields

Abstract

Recent experiments demonstrated unexpected, even intriguing properties of certain glassymaterials in magnetic fields at low temperatures. We have studied the magnetic fielddependence of the static dielectric susceptibility and the heat capacity of glasses at lowtemperatures. We present a theory in which we consider the coupling of the tunnellingmotion to nuclear quadrupoles in order to evaluate the static dielectric susceptibility. In thelimit of weak magnetic field we find the resonant part of the susceptibility increasing likeB2 while for large magneticfield it behaves as 1/B. In the same manner we consider the coupling of the tunnelling motion to nuclearquadrupoles and angular momentum of tunnelling particles in order to find the heatcapacity. Our results show the Schottky peak for the angular momentum part, andB2 dependence for the nuclear quadrupole part of the heat capacity, respectively. We discusswhether or not this approach can provide a suitable explanation for such magneticproperties.