CROSSING OF CONDUCTION- AND VALENCE-SUBBAND LANDAU LEVELS IN AN INVERTED HGTE/CDTE QUANTUM WELL

In the inverted-band regime of HgTe/CdTe quantum wells, the lowest Landau level of the lowest conduction subband and the highest Landau level of the topmost valence subband are predicted to cross at a critical magnetic field ${B}_{c}.$ We study this crossing experimentally with far-infrared Fourier-transform spectroscopy in a gated HgTe/CdTe quantum well with tunable electron density. The crossing point is identified by a characteristic exchange of oscillator strength between the two transitions involved, one being a cyclotron resonance, the other an intersubband resonance. The experimental resonance positions, the oscillator strengths as well as the value of ${B}_{c},$ are in good agreement with theoretical results of a 6\ifmmode\times\else\texttimes\fi{}6 k\ensuremath{\cdot}p model evaluated for the $[211]$ growth direction.