Split Dirac cones in HgTe/CdTe quantum wells due to symmetry-enforced level anticrossing at interfaces

Tarasenko, S. A.; Durnev, M. V.; Nestoklon, M. O.; Ivchenko, E. L.; Luo, Jun-Wei; Zunger, Alex

doi:10.1103/physrevb.91.081302

Cited by 80 publications

(96 citation statements)

References 23 publications

(36 reference statements)

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“…In Ref. [15] it was assumed that the change of the ionicity across the interface may be extracted from the atomic levels obtained in ab initio calculations. Instead, one may introduce more physical parameter, the change of electrostatic potential on anion across the interface, and fit this parameter to reproduce the expected properties of the interface.…”

Section: Comparison With Results Of K · P and Tight-binding Calcumentioning

confidence: 99%

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Spin-orbit splitting of valence and conduction bands in HgTe quantum wells near the Dirac point

et al. 2016

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Energy spectra both of the conduction and valence bands of the HgTe quantum wells with a width close to the Dirac point were studied experimentally. Simultaneous analysis of the Shubnikov-de Haas oscillations and Hall effect over a wide range of electron and hole densities gives surprising result: the top of the valence band is strongly split by spin-orbit interaction while the splitting of the conduction band is absent, within experimental accuracy. Astonishingly, but such a ratio of the splitting values is observed as for structures with normal spectrum so for structures with inverted one. These results do not consistent with the results of kP calculations, in which the smooth electric filed across the quantum well is only reckoned in. It is shown that taking into account the asymmetry of the quantum well interfaces within a tight-binding method gives reasonable agreement with the experimental data.

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Section: Comparison With Results Of K · P and Tight-binding Calcumentioning

confidence: 99%

“…The tight-binding parameters used in calculations were obtained using procedure similar to that described in details in the Supplemental Material to Ref. [15] with the following modification. In Ref.…”

Section: Comparison With Results Of K · P and Tight-binding Calcumentioning

confidence: 99%

Spin-orbit splitting of valence and conduction bands in HgTe quantum wells near the Dirac point

et al. 2016

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“…We note that such phase transition can not be described within the simplified 2D Dirac-type model, 4 because it considers the bulk and edge states only in the vicinity of k = 0. Moreover, any known simplified 2D models 4,23,40,41 are not generally applicable to this case. Therefore, even qualitative picture of the edge states in the SM phase is unknown.…”

Section: B Semimetal Phasementioning

confidence: 99%

Pressure- and temperature-driven phase transitions in HgTe quantum wells

et al. 2016

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We present theoretical investigations of pressure and temperature driven phase transitions in HgTe quantum wells grown on CdTe buffer. Using the 8-band k·p Hamiltonian we calculate evolution of energy band structure at different quantum well width with hydrostatic pressure up to 20 kBar and temperature ranging up 300 K. In particular, we show that in addition to temperature, tuning of hydrostatic pressure allows to drive transitions between semimetal, band insulator and topological insulator phases. Our realistic band structure calculations reveal that the band inversion under hydrostatic pressure and temperature may be accompanied by non-local overlapping between conduction and valence bands. The pressure and temperature phase diagrams are presented.

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“…Figure 5 illustrates the linear dispersion of helical edge states. The edge states with the positive velocity along x direction are formed mainly from |E1,+1/2 and |H 1,+3/2 subbands and have pseudospin s = +1/2 (spin-up branch) [27,28]. Counterpropagating electrons have s = −1/2.…”

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confidence: 99%

Photogalvanic probing of helical edge channels in two-dimensional HgTe topological insulators

et al. 2017

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We report on the observation of a circular photogalvanic current excited by terahertz laser radiation in helical edge channels of two-dimensional (2D) HgTe topological insulators (TIs). The direction of the photocurrent reverses by switching the radiation polarization from a right-handed to a left-handed one and, for fixed photon helicity, is opposite for the opposite edges. The photocurrent is detected in a wide range of gate voltages. With decreasing the Fermi level below the conduction band bottom, the current emerges, reaches a maximum, decreases, changes its sign close to the charge neutrality point (CNP), and again rises. Conductance measured over a ≈3 μm distance at CNP approaches 2e 2 /h, the value characteristic for ballistic transport in 2D TIs. The data reveal that the photocurrent is caused by photoionization of helical edge electrons to the conduction band. We discuss the microscopic model of this phenomenon and compare calculations with experimental data. DOI: 10.1103/PhysRevB.95.201103 The quantum spin Hall (QSH) effect occurs in 2D TIs and rests on the existence of conducting helical edge states while the bulk is insulating [1][2][3][4]. In contrast to the quantum Hall effect, the formation of these edge states requires no magnetic field: they stem from the band inversion caused by strong spin-orbit interaction and are topologically protected by time reversal symmetry. Given that the spin-up and spin-down electrons propagate along an edge in opposite directions, i.e., the spin projection is locked to the k vector, the edge channels are helical in nature. The first experimental evidence for the QSH effect was obtained in HgTe quantum wells (QWs) [5] by observing a resistance plateau around h/2e 2 in the longitudinal resistance of a mesoscopic Hall bar. Here h is Planck's constant and e is the electron charge. This observation was further confirmed by nonlocal experiments in the ballistic [6] and diffusive [7] transport regime. Conducting edge channels were later probed by scanning SQUID microscopy [8], scanning gate microscopy [9], microwave impedance microscopy [10], and by analyzing supercurrents [11]. The spin polarization of the edge states was investigated so far by electrical means only: by detecting the spin to charge conversion in devices utilizing the inverse spin Hall effect [12] or with ferromagnetic contacts [13].Here we use circularly polarized terahertz radiation to excite selectively spin-up and spin-down electrons circling clockwise and counterclockwise around a sample. We show that the excitation causes an imbalance in the electron distribution between positive and negative wave vectors. This is probed as the associated photogalvanic [14,15] current, which reverses its direction upon switching the helicity.The experiments have been carried out on Hg 0.3 Cd 0.7 Te/HgTe/Hg 0.3 Cd 0.7 Te single QW structures with a well width of 8 nm having inverted band ordering. We used this width to maximize the energy gap to about 25 meV [4,5]. Structures were grown by molecular beam epitaxy o...

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Split Dirac cones in HgTe/CdTe quantum wells due to symmetry-enforced level anticrossing at interfaces

Cited by 80 publications

References 23 publications

Spin-orbit splitting of valence and conduction bands in HgTe quantum wells near the Dirac point

Spin-orbit splitting of valence and conduction bands in HgTe quantum wells near the Dirac point

Pressure- and temperature-driven phase transitions in HgTe quantum wells

Photogalvanic probing of helical edge channels in two-dimensional HgTe topological insulators

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