Magnetic breakdown at high fields: semiclassical and quantum treatments

: The effects of finite temperature and noninteracting spins on magnetic breakdown (MB) in a quasi-two-dimensional organic conductor have been determined by computing the field-dependent free energy using a realistic crystal structure with no adjustable parameters. The de Haas-van Alphen oscillation spectra, including the MB phenomena, are thereby obtained microscopically. Within the range of computed magnetic field, from 170 to 1400 T, we find remarkable agreement between the predictions of the semiclassical and quantum treatment. We also find that the Zeeman effect leads to splitting of a frequency corresponding to the fundamental orbit.