Temperature-driven single-valley Dirac fermions in HgTe quantum wells

Abstract

We report on temperature-dependent magnetospectroscopy of two HgTe/CdHgTe quantum wells below and above the critical well thickness $d_c$. Our results, obtained in magnetic fields up to 16 T and temperature range from 2 K to 150 K, clearly indicate a change of the band-gap energy with temperature. The quantum well wider than $d_c$ evidences a temperature-driven transition from topological insulator to semiconductor phases. At the critical temperature of 90 K, the merging of inter- and intra-band transitions in weak magnetic fields clearly specifies the formation of gapless state, revealing the appearance of single-valley massless Dirac fermions with velocity of $5.6\times10^5$ m$\times$s$^{-1}$. For both quantum wells, the energies extracted from experimental data are in good agreement with calculations on the basis of the 8-band Kane Hamiltonian with temperature-dependent parameters.Comment: 5 pages, 3 figures and Supplemental Materials (4 pages

Realistic picture of helical edge states in HgTe quantum wells

“…In this work, we propose a minimal effective 2D model, which describes the side maxima in the valence subband and qualitatively reproduces the band structure calculations based on the Kane Hamiltonian, which validity is confirmed by a large variety of experiments performed by different techniques [2][3][4]6,[25][26][27][28][29][30][31][32][33] . By using the derived 2D Hamiltonian, we explore a picture of the edge states in HgTe-based QSHIs with direct and indirect band gap.…”

Magneto-transport in inverted HgTe quantum wells

“…The cian region is the only one accessible for both permanent magnets and liquid helium systems effects due to lattice constant mismatch, with the parameters confirmed by our earlier investigations. 44,45 According to the calculation results presented in Fig. 3, sample S1 has an inverted band structure up to the critical magnetic field B c ≈ 4 T, at which a crossing of the highest LL from the valence band with the lowest LL from the conduction band occurs.…”

Зонный спектр в гетероструктурах HgTe/CdHgTe p-типа и его перестройка с изменением температуры

“…К настоящему времени теоретически рассматривались возможности осуществления фазового перехода в КЯ HgTe/CdHgTe между состояниями тривиального и топологического изоляторов с помощью внешнего электрического по-ля [20,21], температуры [10,21,22] и давления [22]. Экс-периментально качественное изменение зонного спектра и наличие такого перехода при изменении темпера-туры впервые было продемонстрировано с помощью транспортных [10] и магнитооптических измерений [23]. Было показано, что увеличение температуры приводит к перестройке зонной структуры от инвертированной к нормальной.…”