Temperature and Coupling Strength Dependence of Polaron Effective Mass and Radius

Polaron effective mass and radius are investigated by using path integral methods. The calculations are performed in the framework of the variational principle for the free energy. At low temperatures, a generalization of Feynmans expression for the effective mass and an expression for the polaron radius at arbitrary coupling are obtained. It is shown that at low temperatures, the effective mass increases and the radius decreases with increasing temperatures. This behaviour of the effective mass agrees satisfactorily with cyclotron resonance experiments and is easily explained qualitatively.