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

The nuclear T₁ has been measured between 1.2 and 300 K on ¹¹B, ²³Na, ²⁹Si, and ⁷⁷Se in amorphous B₂{O}₃$, ${({Na}₂O)}0.3(SiO₂)0.7, Na₂{B}₄O₇, and Se. The measured rates, which for spins I>1/2 are much greater than those observed in corresponding crystalline materials, are nearly field independent and vary as T^α with α~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.