High-field cyclotron resonance in the conduction bands of GaSb and effective-mass parameters at theLpoints

We have observed infrared cyclotron resonance in the conduction band at both the Γ and the L points in n-type GaSb at high magnetic fields up to 500 T. We observed cyclotron resonance signals from the Γ and the L points separately for temperatures higher than 100 K. The resonance at the L point was observed in fields higher than 60 T. From the photon-energy dependence of the effective mass for magnetic fields parallel to the 〈100〉 and the 〈111〉 directions, we obtained the longitudinal and the transverse effective masses, $m_l$ and $m_t,$ as $(1.4\mathrm{}\pm {0.2)m}_0$ and $(0.085\mathrm{}\pm {0.006)m}_0$ at the band edge of the L point. The magnetic-field-induced $\Gamma -L$ crossover was estimated to take place at approximately 125 T for magnetic fields parallel to the 〈100〉 direction from the field dependence of the absorption intensity at the Γ and the L points and a calculation of the $N=0\mathrm{}$ Landau levels at the Γ and the L points. The nonparabolicity at the L point is found to be larger than that at the Γ point. For the Γ point, we obtained a band-edge mass of ${0.039m}_0$ from the photon-energy dependence of the effective mass.