On the Energy Spectrum of the Piezoelectric Polaron

The energy spectrum of a piezoelectric polaron is theoretically discussed. At absolute zero temperature, Haga's approximations originally developed for the theory of optical polaron are used for investigating the low excited state. At finite temperature, the intermediate coupling theory is applied to get the free energy and the energy spectrum of the piezoelectric polaron. The energy spectrum is in accord with Porsch's result obtained by a Green function method. The energy spectrum is calculated numerically, which starts out quadratically and becomes approximately linear as the momentum increases. This energy-momentum relationship differs appreciably from that of previous two theories at finite temperature.