Electronic structures of HgTe and CdTe surfaces and HgTe/CdTe interfaces

Schick, Joseph T.; Bose, Shyamalendu M.; Chen, A.-B.

doi:10.1103/physrevb.40.7825

Cited by 8 publications

(9 citation statements)

References 34 publications

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“…One might naively attribute the observed edge conduction in moderate to high fields to trivial edge states, for example due to a unidirectional band bending (Fermi level pinning) or fringing field effect from gating 20 . Such trivial edge states, if exist, are often assumed to be localized and not contributing to transport 21 22 23 . But in this particular material, strong spin-orbit coupling may suppress direct backscattering 24 and thus ‘protect' the conduction via trivial edge states, possibly to mesoscopic lengths.…”

Section: Discussionmentioning

confidence: 99%

“…Moreover, the edge conduction, expected and unexpected, only appears in the 7.5 nm device—suggesting that it cannot be completely ‘trivial', but is related to the thickness-induced band inversion. Additional crucial ingredients may include many-body effects 25 26 27 28 and material specifics of HgTe QW, including its strong spin-orbit coupling, n – p asymmetry, mercury vacancies 21 29 30 and intrinsic surface effect 22 23 . As it stands now, our discovery could herald broadly relevant physics or simply reflect specifics of this material.…”

Section: Discussionmentioning

confidence: 99%

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Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry

et al. 2015

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The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy, and compare our findings to a non-inverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. This indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry

et al. 2015

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“…We believe that testing the degree of sophistication of the lattice-DFT method in a rich context, such as that provided by a three-phase lattice-gas model, can be interesting on fairly general grounds, e.g. for weighing up the superiority, if any, of the DFT over other available statistical methods such as the transfer-matrix [13] and the cluster variational methods [16].…”

Section: Introductionmentioning

confidence: 99%

Density-functional theory of a lattice-gas model with vapour, liquid, and solid phases

Prestipino¹,

Giaquinta

2003

J. Phys.: Condens. Matter

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We use the classical version of the density-functional theory in the weighted-density approximation to build up the entire phase diagram and the interface structure of a two-dimensional lattice-gas model which is known, from previous studies, to possess three stable phases -solid, liquid, and vapour. Following the common practice, the attractive part of the potential is treated in a mean-field-like fashion, although with different prescriptions for the solid and the fluid phases. It turns out that the present theory, compared to similar theories in the continuum, is of worse quality. Nevertheless, at least a number of qualitative facts are reproduced correctly: i) the existence of three phases; ii) the disappearance of the liquid phase when the range of the attraction is progressively reduced; and iii) the intrusion, just below the triple-point temperature, of a liquid-like layer at the interface between the coexisting solid and vapour phases.

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“…On the (001) surface of HgX, both mercury bonds and bonds involving p-orbitals from the first X sub-surface layer are broken. These dangling bonds of the Hg-terminated (001) surface give rise to dispersionless surface bands 31,32 . The Dirac cones emerging from the dangling bonds were found to be strongly anisotropic for HgS 21 , middle panel of Fig.…”

mentioning

confidence: 99%

Engineering Topological Surface States: HgS, HgSe, and HgTe

et al. 2013

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Using density functional electronic structure calculations, we establish the consequences of surface termination and modification on protected surface-states of metacinnabar (β-HgS). Whereas we find that the Dirac cone is isotropic and well-separated from the valence band for the (110) surface, it is highly anisotropic at the pure (001) surface. We demonstrate that the anisotropy is modified by surface passivation because the topological surface-states include contributions from dangling bonds. Such dangling bonds exist on all pure surfaces within the whole class HgX with X = S, Se, or Te and directly affect the properties of the Dirac cone. Surface modifications also alter the spatial location (depth and decay length) of the topologically protected edge-states which renders them essential for the interpretation of photoemission data.PACS numbers: 72.80.Sk An attractive perspective for spintronics was opened up by the discovery 1-3 and manufacturing 4-6 of topological insulators (TIs). Inside, in its bulk, a TI is insulating but on its boundary -the material's edges, surfaces, or interfaces -a TI is conducting. The first TI in which the topological character of its edge-states was established is HgTe, a mercury chalcogenide material of the HgX family (where X=S, Se, Te) with a zinc-blende crystal structure 4 . The understanding of the precise properties of the topological edge-states in the HgX family of TIs -and an understanding of how these can be altered and engineered -is of fundamental importance in the field. It is of course also of direct relevance to the development of future spintronics applications, which aims to exploit the spin-momentum locking of TI boundary electrons 7,8 allowing for instance the generation of edge-spin-currents by circularly polarized light 9-11 . The precise location and electronic structure of the topological surface-states, in particular their dispersion, play furthermore an essential role in determining their spin-transport characteristics. It is for instance well-known that the momentum-spin locking usually renders disordered TIs poor spin conductors: When the electronic spin is tied to its momentum each scattering event randomizes the spin 12,13 . It was recently established that the resulting limit on spin relaxation time τ s for edge-state electrons strongly depends on their dispersion and momentum space anisotropy 14 .Here we show that for the HgX class of mercury-based II-VI semiconductors in the zinc-blende structure there is a strong influence of existing dangling bonds on the properties of topological surface-states. Thus, by surface passivation, it is possible to achieve a strong modification of the spatial location of the topological states, their rate of decay into the bulk, the resulting Dirac cone dispersion and, in particular, the Dirac cone anisotropy. Such alterations are possible because the presence of topological edge-states is absolutely fixed by the topological invariants of the bulk electronic structure, but the shape of their dispersion, their locat...

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Electronic structures of HgTe and CdTe surfaces and HgTe/CdTe interfaces

Cited by 8 publications

References 34 publications

Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry

Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry

Density-functional theory of a lattice-gas model with vapour, liquid, and solid phases

Engineering Topological Surface States: HgS, HgSe, and HgTe

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