Strong-Coupled Piezoelectric Polaron

We formulate the "piezoelectric polaron" problem in such a way that it can be expanded in inverse powers of the coupling constant α. We show that the lowest-order terms are identical to those for the "optical polaron." The next order, which depends on the dynamical properties of the lattice, yields results differing from those for the optical polaron. In this approximation we calculate the effective mass, which is proportional to α² (rather than α⁴, as it is for the optical polaron).