Extra-long hole spin relaxation time in InGaAs/GaAs quantum wells probed by cyclotron resonance spectroscopy

We report a long, ms range, spin relaxation time of holes in InGaAs/GaAs quantum wells probed by cyclotron-resonance spectroscopy in pulsed magnetic fields up to 60 Tesla. We found a strong hysteresis in the spectral weights of the cyclotron resonance absorption when a rapidly changing magnetic field is used for the experiment, while the hysteresis vanishes when a much slower changing magnetic field is used. We attribute this behavior to a long, comparable to the magnetic-field rise time, energy relaxation time between the two lowest spin-split hole Landau levels, i.e., a long hole spin relaxation time.