Landau level spectroscopy of valence bands in HgTe quantum wells: Effects of symmetry lowering

TL;DR

This study uses Landau level spectroscopy to investigate the valence band structure in HgTe quantum wells, revealing limitations of the standard model and the importance of symmetry-breaking effects for accurate descriptions.

Contribution

The paper demonstrates that including bulk and interface inversion asymmetries in the model better explains experimental magneto-optical responses in HgTe quantum wells.

Findings

Standard 4-band Kane model is insufficient to explain observed phenomena.

Inversion asymmetries significantly alter valence band structure.

Experimental data shows avoided crossings and forbidden transitions.

Abstract

Landau level spectroscopy has been employed to probe the electronic structure of the valence band in a series of p-type HgTe/HgCdTe quantum wells with both normal and inverted ordering of bands. We find that the standard axial-symmetric 4-band Kane model, which is nowadays widely applied in physics of HgTe-based topological materials, does not fully account for the complex magneto-optical response observed in our experiments - notably, for the unexpected avoided crossings of excitations and for the appearance of transitions that are electric-dipole forbidden within this model. Nevertheless, reasonable agreement with experiments is achieved when the standard model is expanded to include effects of bulk and interface inversion asymmetries. These remove the axial symmetry, and among other, profoundly modify the shape of valence bands.