Crossover to quantum tunneling and relaxation in dipolar glasses

Abstract

Arrhenius plots of mean relaxation rates in dipolar glasses often show deviations from linear behavior at low temperatures. The upward curvature in these plots is usually attributed to quantum tunneling solely on the basis that a quantum tunneling rate should have a finite, nonzero value, at $T=0,$ without further quantitative analysis of experimental data. We find that experimental data of relaxation in several dipolar glasses fits quite well to detailed theoretical predictions for the crossover region between classical activation and quantum tunneling. The values of the parameters of the metastable potential barriers obtained from the fits raise some interesting questions about these often quoted deviations from Arrhenius behavior.