The search for tunnelling states in bulk silicon disordered by fast neutron irradiation

Low-temperature studies on amorphous and partly disordered low-coordinated solids have given evidence for the presence of low-energy excitations which can be described as quantummechanical tunneling states. In higher coordinated materials however, the presence of tunneling states has been discussed for a long time. This paper gives an overview of the study we have performed in order to contribute to this discussion on the possible "glassy" behavior of high coordinated materials. It includes ultrasonic attenuation and velocity measurements, as well as Raman spectroscopy performed on fast neutron irradiated silicon. The results of these experiments indicate the presence of tunneling states in this high coordinated material.