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

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 experimentsnotably, 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.

Optical Studies and Transmission Electron Microscopy of HgCdTe Quantum Well Heterostructures for Very Long Wavelength Lasers

“…Figure 3 a shows a false-color plot of relative magneto-transmission of structure#A0130 at 4.2 K.One may immediately recognize the most pronounced interband transitions α- and βin the energy range from 70 to 100meV, reported earlier for structures with single QWs [ 27 , 39 ]. Nonetheless, observation of additional absorption features at higher energies provides obvious benefits for comparison with calculated transitions, following the procedure described earlier [ 27 ].…”

Experimental Observation of Temperature-Driven Topological Phase Transition in HgTe/CdHgTe Quantum Wells

“…For electric-dipole excitations in Faraday geometry a transition can change LL number N by ±1 and cannot change its spin projection on the z axis. Transition α′ is not allowed because it changes the LL number by 3 and β′ implies a spin flip (for more details see e.g., [14]). The corresponding lines, however, can be observed because of mixing of the zero-mode LLs near the crossing point [9,15] (line α′ is shown on Figure 2f).…”

Many-particle effects in optical transitions from zero-mode Landau levels in HgTe quantum wells

“…Particularly, the measurements of magnetotransport [4,5,16,17] and photoconductivity [18,19] per-formed with gated Hall bars show that the anticrossing gap is negligibly small. On the contrary, the farinfrared magnetospectroscopy reveals a fine structure of the optical transitions from zero-mode LLs [20][21][22][23]. The analysis of this fine structure in the vicinity of B c within the Dirac-like model, including BIA and IIA, gives ∆ ∼ 5 meV for the joint effects.…”

“…The analysis of this fine structure in the vicinity of B c within the Dirac-like model, including BIA and IIA, gives ∆ ∼ 5 meV for the joint effects. These contested experimental values of the anticrossing gap obtained in magnetotransport and magnetospectroscopy triggered a vivid discussion about the real strength of BIA and IIA in HgTe QWs [5,[23][24][25].…”