New Phonon Echo-Signals Due to the Two-Level Systems in Glasses

Abstract

A theory of the microwave tunnel phonon echo excited by long acoustic pulses in glass is developed. We take into account a large broadening of the two-level system (TLS) energy levels, a broad distribution of glassy parameters through their averaging with some distribution functions, TLS potential asymmetry as well as a tunneling parameter, dipole–dipole interaction between TLS and echo decay. For the first time new subsidiary phonon echo signals excited by long acoustic pulses are found. New echoes appear due to the asymmetry of the TLS potential. These signals are less intensive than basic echo. They have unusual orientational dependence. The intensities, form and moments of generation of echo signals are calculated. It is shown that the broad distribution of glassy parameters results in the change of echo amplitude, echo form and echo decay character. The amplitude and form of echoes in glass depend on the amplitude and length of external exciting pulses. The delay effects in time moments of echo generation are found. The estimations shown a possibility for the experimental display of the basic and subsidiary echo signals. A corresponding experiment relative to observing of the new echoes is proposed.