ANISOTROPIC TUNNELING STATES IN NEUTRON-IRRADIATED QUARTZ

As a contribution to the study of the dynamic anomalies in amorphous SiO2, ultrasonic absorption measurements were carried out in neutron-irradiated z-cut quartz. In this paper, the data are quantitatively analyzed with the tunneling model, proposed for amorphous solids. From the numerical fits, the tunneling state parameters can be calculated and the values found for three different frequencies are consistent with each other. A comparison with the results obtained in x-cut quartz reveals a remarkable anisotropy in the coupling of the tunneling states with the phonons: for the studied dose, the coupling in z-cut quartz turns out to be only two-thirds of the value found in a similar x-cut sample.