The Microwave Study of Bottleneck Effect and Relaxation of Resonant Phonons Emitted from the Tunneling Li+Ion in KCl

Abstract

The microwave pulse excitation and subsequent relaxation of the tunneling Li + ion in KCl have been studied at 9.4 GHz, using the paraelectric resonance, the microwave saturation recovery and the microwave double resonance (MDR) developed newly. From the MDR, the absorption between A 2u - T 2g in the ground state tunneling quartet is expressed by a line with half-width of 0.6 GHz peaked at 8.5 GHz. The energy relaxation time T b depends on the thickness of specimen L and temperature T as T b (msec)≃ L (cm)· T ( K ). Abrupt decrease of T b is found when the specimen is immersed in He II. These data are explained in terms of the bottleneck effect of resonant phonon (RP) emitted from the microwave pumped system. The lifetime T ph of the RP is governed by its extinction at a two-level system on the surface with a rate of 0.01/reflection. The relation T b = T ph is derived after reducing the quartet to doublet.