Theory of magnetophonon structure in the longitudinal magnetothermal emf

The magnetophonon effect, as manifested in the longitudinal magnetothermal emf (Seebeck coefficient Qzz), is examined analytically and numerically in the limit of no Landau-level broadening, for combined optic and acoustic-phonon scattering of electrons in nonpolar semiconductors. In addition to off-resonance maxima occurring at magnetic fields somewhat larger than those given by the Gurevich-Firsov resonance condition Nωc=ω₀, N=1,2,, where ωc and ω₀ are the cyclotron and optic-phonon frequencies, discontinuities in the derivative of Qzz with respect to magnetic field are found. The slope discontinuities lie precisely at Nωc=ω₀ and at ($2n+1$) ωc=2ω₀, n=0,1,, yielding additional structure characterized by ∂|Qzz|∂B_->∂|Qzz|∂B₊ at all temperatures and degrees of elastic scattering.