Nuclear Spin-Lattice Relaxation Associated with Low-Energy Excitations in Glasses

Abstract

The nuclear ${T}_{1}$ has been measured between 1.2 and 300 K on $^{11}\mathrm{B}$, $^{23}\mathrm{Na}$, $^{29}\mathrm{Si}$, and $^{77}\mathrm{Se}$ in amorphous ${\mathrm{B}}_{2}$${\mathrm{O}}_{3}$, ${({\mathrm{Na}}_{2}\mathrm{O})}_{0.3}$${(\mathrm{S}\mathrm{i}{\mathrm{O}}_{2})}_{0.7}$, ${\mathrm{Na}}_{2}$${\mathrm{B}}_{4}$${\mathrm{O}}_{7}$, and Se. The measured rates, which for spins $I>\frac{1}{2}$ are much greater than those observed in corresponding crystalline materials, are nearly field independent and vary as ${T}^{\ensuremath{\alpha}}$ with $\ensuremath{\alpha}\ensuremath{\sim}1.3$. Such a quadrupolar relaxation might be explained by a model involving the distribution of two-level systems, as describes the anomalous thermal and ultrasonic-wave properties of similar materials.