Spectroscopy of Temperature-Driven Single Valley Dirac Fermions in HgTe/CdHgTe Quantum Wells

We report on the temperature-dependent magneto-absorption and magnetotransport spectroscopy of HgTe/CdHgTe quantum wells above the critical well thickness d
_c
. Our results, obtained in magnetic fields up to 16 T and temperature range from 1.7 to 150 K, clearly indicate a change in the band-gap energy with temperature. A topological phase transition between quantum spin Hall and trivial insulator states, revealing appearance of single-valley Dirac fermions at T= 27 and 90 K for 6.5 and 8 nm QWs respectively, was clearly observed in our magnetospectroscopy measurements.