Observing electronic structures on <i>ex‐situ</i> grown topological insulator thin films

Yao, Shu‐Hua; Zhou, Bo; Lu, M.; Liu, Z. K.; Chen, Y. B.; Analytis, James; Brüne, C.; Dang, Wenhui; Mo, S.-K.; Shen, Zhi‐Xun; Fisher, I. R.; Molenkamp, L. W.; Peng, Hailin; Hussain, Zahid; Chen, Y. L.

doi:10.1002/pssr.201206400

Cited by 10 publications

(10 citation statements)

References 34 publications

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“…[19][20][21] We studied a HgTe (001) surface that was grown in recent experiments. 10,22 Our optimized equilibrium lattice constant was 6.438Å, which is close to the experimental value of 6.461Å(Ref. 23).…”

Section: Methodssupporting

confidence: 84%

“…29). However, these dangling bond states were not reported in experimental results, 10,22,28 which may indicate a cleaved surface in ARPES with various coexisting terminations. This is similar to the TlBiSe 2 type of TIs, where tight-binding calculations 30 predicted surface states more consistent with experiments 31-33 than those from ab initio simulations, 34 in which mixed Tl and Se terminations were revealed recently by scanning tunneling microscopy.…”

mentioning

confidence: 96%

“…This is also consistent with recent ARPES measurements. 10,22,28 We note that it might be necessary to take these two types of surface states into account when interpreting future ARPES and transport experiments.…”

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confidence: 99%

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Ab initio study of topological surface states of strained HgTe

Wu¹,

Yan²,

Felser³

2014

EPL

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The topological surface states of mercury telluride (HgTe) are studied by ab initio calculations assuming different strains and surface terminations. For the Te-terminated surface, a single Dirac cone exists at the Γ point. The Dirac point shifts up from the bulk valence bands into the energy gap when the substrate-induced strain increases. At the experimental strain value (0.3%), the Dirac point lies slightly below the bulk valence band maximum. A left-handed spin texture was observed in the upper Dirac cone, similar to that of the Bi2Se3-type topological insulator. For the Hg-terminated surface, three Dirac cones appear at three time-reversal-invariant momenta, excluding the Γ point, with nontrivial spin textures.

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Section: Methodssupporting

confidence: 84%

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confidence: 96%

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Ab initio study of topological surface states of strained HgTe

Wu¹,

Yan²,

Felser³

2014

EPL

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“…For an application of the exotic surface states of TI to electronic or spintronic devices, one of the most promising candidates are epitaxially grown films of TIs, such as Bi 2 Se 3 on SiC(0001) [9] and Si(111) [10,11], HgTe on CdTe(001) [12][13][14], and -Sn on InSb(001) [15]. The growth on semiconductor substrates makes them easy to combine with usual semiconductor electronic devices.…”

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confidence: 99%

“…Furthermore, the epitaxial growth itself enables to manipulate the electronic structure of grown TI films. Structural strain introduced from a lattice mismatch with the substrate opens a band gap in bulk bands of HgTe [12][13][14] or -Sn [15] films for thicknesses between 0.1 to 1 m. While the size of the band gap is only a few tens of meV, it is very important for these films as a TI; neither -Sn nor HgTe without any strain are TIs but zero-gap semimetal. Quantum-size effect (QSE) [16] from film thicknesses changes the electronic structure of TI even further.…”

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confidence: 99%

Dirac Cone with Helical Spin Polarization in Ultrathinα-Sn(001) Films

et al. 2013

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Spin-split two-dimensional electronic states have been observed on ultrathin Sn(001) films grown on InSb(001) substrates. Angle-resolved photoelectron spectroscopy (ARPES) performed on these films revealed Dirac-cone-like linear dispersion around the Γ¯ point of the surface Brillouin zone, suggesting nearly massless electrons belonging to 2D surface states. The states disperse across a band gap between bulklike quantum well states in the films. Moreover, both circular dichroism of ARPES and spin-resolved ARPES studies show helical spin polarization of the Dirac-cone-like surface states, suggesting a topologically protected character as in a bulk topological insulator (TI). These results indicate that a quasi-3D TI phase can be realized in ultrathin films of zero-gap semiconductors.

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Magnetic Topological Insulator Heterostructures: A Review

Liu

Hesjedal

2021

Advanced Materials

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Chern number corresponds to the occupancy of discrete Landau levels, which can be varied by tuning the Fermi energy via a gate voltage. It further corresponds to the number of dissipationless conduction channels in the gapless edge state of the quantum Hall insulator that is insulating in the bulk in high magnetic fields.After observing the quantum version of the Hall effect, the natural question to ask is if there is also a quantized version of the anomalous Hall effect (AHE), commonly observed in ferromagnets. This quantum anomalous Hall effect (QAHE) would then be observable in the absence of external fields. The QAHE was initially proposed to arise in 2D honeycomb or kagome lattices, such as monolayer graphene, that host a non-zero out-of-plane magnetic flux density, but zero net flux in each unit cell. [8,9] Later, it was also proposed that the QAHE may be found in Hg 1−y Mn y Te quantum wells without an external magnetic field, in which the effect arises purely due to the spin polarization of the Mn atoms. [10] However, the experimental realization of the QAHE was not reported until 2013, when transport in 3D topological insulators (TIs) doped with magnetic impurities was studied. TIs refer to a class of materials that is insulating in the bulk, but which possess topologically protected conducting surface states. Right from the start, the field was (see refs. [6,11-17]), and continues to be (see refs. [18-20]), to a large degree driven by theory. Common examples of 3D TIs are rhombohedral Bi 2 Se 3 , Bi 2 Te 3 , and Sb 2 Te 3 . [15] The surface state of a TI consists of two linearly dispersing states connecting the bulk conduction and valence bands. The two states cross at one point in reciprocal space, the Dirac point (Figure 1a). The charge carriers in this band structure are massless fermions, which are described by the relativistic Dirac equation. [15] Due to the strong spin-orbit coupling (SOC) in these materials, surface electron spins are locked to their momentum, forming dissipationless, counter-propagating conduction channels in the surface state.By introducing magnetism to a TI, either by impurity doping with magnetic elements, by proximity coupling to a magnetic insulators (MIs), or other magnetic layers, time-reversal symmetry (TRS) can be broken. TRS breaking can induce a bandgap in the surface states, leading to the realization of the QAHE which is characterized by 1D chiral edge conduction in zerofield at remanence, as shown in Figure 1. The Chern number, here being +1 or -1, corresponds to the direction of the spinmomentum locked edge current that can be flipped by a (small) external field. Using first-principles calculations, Sb 2 Te 3 , Bi 2 Te 3 , Topological insulators (TIs) provide intriguing prospects for the future of spintronics due to their large spin-orbit coupling and dissipationless, counterpropagating conduction channels in the surface state. The combination of topological properties and magnetic order can lead to new quantum states including the quantum anomalous Hall effect th...

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Observing electronic structures on ex‐situ grown topological insulator thin films

Cited by 10 publications

References 34 publications

Ab initio study of topological surface states of strained HgTe

Ab initio study of topological surface states of strained HgTe

Dirac Cone with Helical Spin Polarization in Ultrathinα-Sn(001) Films

Magnetic Topological Insulator Heterostructures: A Review

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