Ref HAL: hal-04304349_v1
DOI: 10.1109/irmmw-thz57677.2023.10298862
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Résumé:

We report on the emission of Terahertz radiation from Landau quantized Dirac electrons in HgTe/CdHgTe based quantum wells. We show that this cyclotron emission is continuously tunable with magnetic field from 500 GHz up to 2.5 THz. Moreover, given the relativistic nature of charge carriers, the cyclotron mass and therefore the emitted frequency are also tunable with the electron density. These results pave the way for the long-awaited Landau laser which could additionally be tunable by a gate voltage with a fixed magnetic field.

Ref HAL: hal-04304435_v1
Ref Arxiv: 2308.13440
DOI: 10.48550/arXiv.2308.13440
Ref. & Cit.: NASA ADS
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By using the self-consistent Born approximation, we investigate disorder effect induced by shortrange impurities on the band-gap of a seminal two-dimensional (2D) system, whose phase diagram contains trivial, single-band-inverted and double-band-inverted states. Following the density-ofstates (DOS) evolution, we demonstrate multiple closings and openings of the band-gap with the increase of the disorder strength. Calculations of the spectral function describing the quasiparticles at the Γ point of the Brillouin zone evidence that the observed band-gap behavior is unambiguously caused by the topological phase transitions due to the mutual inversions between the first and second electron-like and hole-like subbands. We also find that an increase in the disorder strength in the double-inverted state always leads to the band-gap closing due to the overlap of the tails of DOS from conduction and valence subbands.

Ref HAL: hal-03824970_v1
DOI: 10.21203/rs.3.rs-1630601/v1
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Abstract Since the emergence of graphene, we have seen several proposals for the realization of Landau lasers tunable over the terahertz frequency range. The hope was that the non-equidistance of the Landau levels from Dirac fermions would suppress the harmful non-radiative Auger recombination. Unfortunately, even with this non-equidistance an unfavorable non-radiative process persists in Landau-quantized graphene, and so far no cyclotron emission from Dirac fermions has been reported. One way to eliminate this last non-radiative process is to sufficiently modify the dispersion of the Landau levels by opening a small gap in the linear band structure. A proven example of such gapped graphene-like materials are HgTe quantum wells close to the topological phase transition. In this work, we experimentally demonstrate Landau emission from Dirac fermions in such HgTe quantum wells, where the emission is tunable by both the magnetic field and the carrier concentration. Consequently, these results represent an advance in the realization of terahertz Landau lasers tunable by magnetic field and gate-voltage.

Ref HAL: hal-03824753_v1
Ref Arxiv: 2110.11076
DOI: 10.1103/PhysRevB.105.125203
WoS: WOS:000800753300003
Ref. & Cit.: NASA ADS
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Using an elegant model involving only Γ6c and Γ8v bands, massless Kane fermions were defined as the particles associated with the peculiar band structure of gapless HgCdTe crystals. Although their dispersion relation resembles that of a pseudo-spin-1 Dirac semimetal, these particles were originally considered to be hybrids of pseudospin-1 and -1/2 fermions. Here we unequivocally find that by considering an additional Γ7c conduction band inherent in HgCdTe crystals, the Kane fermions are ultimately two nested Dirac particles. This observation allows the direct application of Lorentz transformations to describe the relativistic behavior of these particles in crossed electric and magnetic fields. By studying the relativistic collapse of their Landau levels at different orientations between the crossed fields and the main crystallographic axes, we demonstrate that the Kane fermions strikingly decay into two independent Dirac particles with increasing of electric field. Our results provide new insight into semi-relativistic effects in narrow-gap semiconductors in crossed electric and magnetic fields.

Ref HAL: hal-03783120_v1
Ref Arxiv: 2206.14561
DOI: 10.1103/PhysRevB.106.115203
Ref. & Cit.: NASA ADS
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Résumé:

Using the self-consistent Born approximation, we study a topological phase transition appearing in bulk HgCdTe crystals induced uncorrelated disorder due to both randomly distributed impurities and fluctuations in Cd composition. By following the density-of-states evolution, we clearly demonstrate the topological phase transition, which can be understood in terms of the disorder-renormalized mass of Kane fermions. We find that the presence of a heavy-hole band in HgCdTe crystals leads to the topological phase transition at much lower disorder strength than is expected for conventional three-dimensional topological insulators. Our theoretical results can also be applied to other narrow-gap zinc-blende semiconductors such as InAs, InSb, and their ternary alloys InAsSb.

Commentaires: 8 pages, 4 figures

Ref HAL: hal-03442316_v1
Ref Arxiv: 2111.07581
Ref. & Cit.: NASA ADS
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HgTe quantum wells with a thickness of ${\sim}$7 nm may have a graphene-like band structure and have been recently proposed to be potential candidates for quantum Hall effect (QHE) resistance standards under the condition of operation in the fields above certain critical field $B_c$, above which the topological phase (with parasitic edge conduction) disappears. We present experimental studies of the magnetoresistance of different of HgTe quantum wells as a function temperature and magnetic field, determining the critical magnetic field $B_c$. We demonstrate that for QWs of specific width $B_c$ becomes low enough to grant observation of remarkably wide QHE plateaus at the filling factor ${v=-1}$ (holes) in relaxed cryomagnetic conditions: while using commercial 0.82 T Neodymium permanent magnets and temperature of a few Kelvin provided by ${^4He}$ liquid system only. Band structure calculations allow us to explain qualitatively observed phenomena due to the interplay between light holes and heavy holes energy sub-bands (side maxima of the valence band). Our work clearly shows that the peculiar band structure properties of HgTe QWs with massless Dirac fermions make them an ideal platform for developing metrological devices with relaxed cryomagnetic conditions.

Ref HAL: hal-03351532_v1
DOI: 10.1134/S0021364020200059
WoS: WOS:000601541600009
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Résumé:

Magneto-absorption in HgTe/CdHgTe quantum wells with an inverted band structure in magnetic fields up to 30 T has been studied. It has been shown that the positions of magneto-absorption lines for transitions from the zero-mode Landau levels in a wide range of magnetic field cannot in principle be described in the “single-electron” approximation using the eight-band Kane model even taking into account effects associated with the absence of spatial inversion symmetry. The revealed dependence of the energies of optical transitions on the magnetic field can be qualitatively explained within a “many-body” picture, where transitions between Landau levels are considered as collective modes hybridized by the electron-electron interaction.