Effects of nonequilibrium electron distribution and electron-electron interaction observed in spin-split cyclotron resonance of InAs/AlSb single quantum wells at high magnetic fields

We have observed two remarkable phenomena in spin-split cyclotron resonance of InAs/AlSb single quantum wells under short-pulse high magnetic fields produced by the single-turn coil technique. The first phenomenon is a hysteretic phenomenon, which was observed with a rapid sweep of the magnetic field in increasing and decreasing directions (∼100 T in a few microseconds). The sweep-rate dependence of the cyclotron resonance spectra revealed that the hysteretic phenomenon is attributable to the nonequilibrium electron distribution in the lowest Landau levels $\mathrm{}(N=0\mathrm{})\mathrm{}$ with plus and minus spins induced by short-pulse high magnetic fields. At low temperatures of around 15 K, a disagreement in intensity between the two different spins is observed in such a way that the total intensity is conserved. The hysteresis is attributed to a slow spin-flip relaxation between the two spin states of the $N=0\mathrm{}$ Landau level with a time constant of 1 μs comparable with the field pulse duration. At high temperatures of around 100 K, a different type of hysteresis is found, where the absorption intensity of the minus spin is smaller in the down sweep than in the up sweep. The sweep-rate dependence shows that the up sweep does not change significantly, but the minus spin decreases with increasing the sweep rate in the down sweep. This is attributed to a slow electron transfer from donor levels in AlSb to a Landau level in InAs. The second phenomenon is the electron-electron interaction effect on the spin-split cyclotron resonance, which displays an intriguing dependence on the filling factor ν and the temperature at around 45 T, where $0.3<~\nu <~\mathrm{1.2.}$ With increasing temperature, the absorption intensity of the down spin increases, exceeding the amount expected from the Boltzmann distribution, while that of the up spin shows the opposite behavior. For samples with different carrier concentrations, the spin splitting at $\nu =0.7\mathrm{}$ is smaller than that at $\nu =0.4\mathrm{}$ by 1 T at around 50 K. These features can be explained qualitatively by a recent theory by Asano and Ando that calculates the effect of the electron-electron interaction on cyclotron resonance spectra by numerical diagonalization for a finite-size system with a finite number of electrons.