High Phonon Frequency Approximation in the Calculation of Phonon Drag Magnetothermopower

At high magnetic fields and low temperatures the phonon drag magnetothermopower is dominated by phonons with energies much greater than k_BT. This fact is used to develop an approximate formula which can be evaluated in a few percent of the time required by the rigorous result. We show that the predominant contribution to the magnetothermopower comes from the transition process in which both the initial Landau level and the final Landau level have the same quantum number n = n'= n_f where nf distinguishes the level nearest to the Fermi energy. A double summation over n and n'can therefore be neglected. In the temperature range of 1.275 K to 5.005 K, all the HPFA results agree with the experimental data and the rigorous theoretical results qualitatively. At T = 2.495 and 2.937 K, the HPFA results arein fair quantitative accordance with the experimental data and the rigorous theoretical results.