Zur Zweibändertheorie der galvano- und thermomagnetischen Transversaleffekte

Abstract

According to the two-band model, formulas for the coefficients of electrical and thermal conductivity, Hall, Ettingshausen, Nernst and Righi-Leduc effect are derived for the two cases of energy dependence of electron free path most important in practice. The use of the general form of Fermi-statistics, valid for any degree of degeneration of the electron gas, allows a common treatment of metals and semiconductors. From the formulas the behaviour of the effects and their interrelations are discussed and, in addition to it, a qualitative interpretation is given on the basis of a simplified model. The pecularities of the behaviour in the case of mixed conductivity are explained by the influence of ambipolar diffusion of charge carriers. This influence is noticeable only if degeneration is weak, except for Nernst and Ettingshausen effect where it determines sign and value of the effects in any case. Thus the differences between the behaviour of the various effects in metals and semiconductors are explained. The possibility of using the results to explain also a recently observed anomaly of the ferromagnetic extraordinary Righi-Leduc effect in Ni-Cu alloys is discussed at the end.