Tuning the Chern number in quantum anomalous Hall insulators

Zhao, Yi; Zhang, Ruoxi; Mei, Ruobing; Zhou, Ling-Jie; Yi, Hemian; Zhang, Ya Qi; Yu, Jiabin; Xiao, Run; Wang, Ke; Samarth, N.; Chan, Moses H. W.; Liu, Chao Xing; Chang, Cui Zu

doi:10.1038/s41586-020-3020-3

Cited by 134 publications

(124 citation statements)

References 33 publications

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“…It can be used to build heterostructures to study exotic topological states, such as topological magnetoelectric effect, axion insulator and high-Chern-number insulator. [47,48] Nevertheless, the apparent distinct behavior of the doped samples in comparison to the pure ones suggests that further theoretical considerations are required for a full understanding.…”

Section: Discussionmentioning

confidence: 99%

Quantum Oscillations in Ferromagnetic (Sb, V)₂Te₃ Topological Insulator Thin Films

et al. 2021

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3d-element dopants. Hence, the broken time-reversal symmetry may enable the detection of the quantum anomalous Hall effect (QAHE) due to the presence of dissipationless edge states. [10][11][12] The combination of such devices with conventional superconductors were predicted to host Majorana fermions, which are suitable for braiding devices for use in topological quantum computers. [13,14] As the band structure of real materials is complex, it is challenging to realize the QAHE or Majorana fermions at a higher temperature. Highly precise band structure engineering is required to suppress the contribution of the bulk bands effectively. To date, this has posed one of the main limiting barriers to the development of practical devices based on the QAHE. Therefore, a deeper understanding of how the band structure of TI can be artificially designed is inevitable.Shubnikov-de Hass (SdH) oscillations are a quantum coherence phenomenon commonly observed in clean metals, where the charge carriers can complete at least one full cyclotron motion without impurity scattering under magnetic field. [15] Wealth parameters such as the Fermi surface topology and mean-free path can be extracted from the oscillation period and the temperature-dependent amplitude variation. [16] Quantum oscillations have been extensively used as a tool to study high temperature superconductors and topological materials. [17][18][19][20] The recent observation of the three-dimensional (3D) quantum Hall effect (QHE) in ZrTe 5 has attracted further enthusiasm to study of quantum oscillations in TI materials. [21] Quantum oscillations have been observed in binary compounds, Bi 2 Se 3 , Bi 2 Te 3 , and Sb 2 Te 3 bulk crystals and thin flakes. [22][23][24][25] In these systems, the oscillations originate from either the surface states or the bulk bands, depending on the position of the chemical potential. [26] Recently, quantum oscillations were discovered in 3d elements doped TI single crystals, such as Fe-doped Sb 2 Te 3 and V doped (Bi, Sn, Sb) 2 (Te, S) 3 . [24,27] However, no long-range FM order was observed. The results motivated the preparation of thin films of similar materials with the potential for FM order coexisting with high mobility topological surface states.So far, to our knowledge, there are only a few reports on the observation of quantum oscillations in magnetically doped TIs, such as V-doped (Bi, Sb) 2 Te 3 , Sm-doped Bi 2 Se 3 . [28,29] However,effective way of manipulating 2D surface states in magnetic topological insulators may open a new route for quantum technologies based on the quantum anomalous Hall effect. The doping-dependent evolution of the electronic band structure in the topological insulator Sb 2−x V x Te 3 (0 ≤ x ≤ 0.102) thin films is studied by means of electrical transport. Sb 2−x V x Te 3 thin films were prepared by molecular beam epitaxy, and Shubnikov-de Hass (SdH) oscillations are observed in both the longitudinal and transverse transport channels. Doping with the 3d element, vanadium, induces long-range ferromagne...

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Section: Discussionmentioning

confidence: 99%

Quantum Oscillations in Ferromagnetic (Sb, V)₂Te₃ Topological Insulator Thin Films

et al. 2021

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“…[ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ] Furthermore, it was suggested that the topologically protected 1D hinge state of 3D SOTIs sheds new light on the development of novel electronic applications based on Majorana bound states and surface quantum anomalous Hall effect, such as topological quantum computers and chiral circuit interconnects. [ 18 , 19 ] However to date, few realistic materials have been identified experimentally as 3D SOTIs. [ 18 , 20 ] A natural question to ask is whether a broad class of 3D SOTIs can be found experimentally.…”

Section: Introductionmentioning

confidence: 99%

Persistence of Monoclinic Crystal Structure in 3D Second‐Order Topological Insulator Candidate 1T′‐MoTe₂ Thin Flake Without Structural Phase Transition

Huang

Hou

et al. 2021

Advanced Science

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A van der Waals material, MoTe 2 with a monoclinic 1T′ crystal structure is a candidate for 3D second-order topological insulators (SOTIs) hosting gapless hinge states and insulating surface states. However, due to the temperature-induced structural phase transition, the monoclinic 1T′ structure of MoTe 2 is transformed into the orthorhombic T d structure as the temperature is lowered, which hinders the experimental verification and electronic applications of the predicted SOTI state at low temperatures. Here, systematic Raman spectroscopy studies of the exfoliated MoTe 2 thin flakes with variable thicknesses at different temperatures, are presented. As a spectroscopic signature of the orthorhombic T d structure of MoTe 2 , the out-of-plane vibration mode D at ≈ 125 cm -1 is always visible below a certain temperature in the multilayer flakes thicker than ≈ 27.7 nm, but vanishes in the temperature range from 80 to 320 K when the flake thickness becomes lower than ≈ 19.5 nm. The absence of the out-of-plane vibration mode D in the Raman spectra here demonstrates not only the disappearance of the monoclinic-to-orthorhombic phase transition but also the persistence of the monoclinic 1T′ structure in the MoTe 2 thin flakes thinner than ≈ 19.5 nm at low temperatures down to 80 K, which may be caused by the high enough density of the holes introduced during the gold-enhanced exfoliation process and exposure to air. The MoTe 2 thin flakes with the low-temperature monoclinic 1T′ structure provide a material platform for realizing SOTI states in van der Waals materials at low temperatures, which paves the way for developing a new generation of electronic devices based on SOTIs.

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“…The band-gap in a Chern insulator can be as small as 10 meV for silicene with transition metal adatoms [97] or as large as 340 meV for stanene honeycomb lattices in which one sublattice is passivated by halide atoms, whilst the other sublattice is not [98]. For E gap ∼ 10 meV, the high temperature limit is 18.5 K, whilst for E gap ∼ 340 meV, the high temperature limit is much larger at 627 K. The ferromagnetic transition temperature is typically of the order of milli-Kelvins [80,99] or a few Kelvins [100], though ferromagnetic transitions as high as T = 243 K (for passivated stanene) and T = 509 K (for passivated germanene) have also been predicted [98]. If the ferromagnetic transition temperature T f is larger than E gap /(2πk B ), we can imagine setting the Chern insulators at a temperature larger than E gap /(2πk B ) but still lower than T f so that the Casimir-Lifshitz energy is again dominated by the zero (Matsubara) frequency contribution, for which the Hall conductivity is quantized and the longitudinal conductivity vanishes; correspondingly, the force can be made repulsive.…”

Section: Casimir Repulsion Between Chern Insulatorsmentioning

confidence: 99%

The Casimir Effect in Topological Matter

2021

Universe

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We give an overview of the work done during the past ten years on the Casimir interaction in electronic topological materials, our focus being solids, which possess surface or bulk electronic band structures with nontrivial topologies, which can be evinced through optical properties that are characterizable in terms of nonzero topological invariants. The examples we review are three-dimensional magnetic topological insulators, two-dimensional Chern insulators, graphene monolayers exhibiting the relativistic quantum Hall effect, and time reversal symmetry-broken Weyl semimetals, which are fascinating systems in the context of Casimir physics. Firstly, this is for the reason that they possess electromagnetic properties characterizable by axial vectors (because of time reversal symmetry breaking), and, depending on the mutual orientation of a pair of such axial vectors, two systems can experience a repulsive Casimir–Lifshitz force, even though they may be dielectrically identical. Secondly, the repulsion thus generated is potentially robust against weak disorder, as such repulsion is associated with the Hall conductivity that is topologically protected in the zero-frequency limit. Finally, the far-field low-temperature behavior of the Casimir force of such systems can provide signatures of topological quantization.

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Tuning the Chern number in quantum anomalous Hall insulators

Cited by 134 publications

References 33 publications

Quantum Oscillations in Ferromagnetic (Sb, V)₂Te₃ Topological Insulator Thin Films

Quantum Oscillations in Ferromagnetic (Sb, V)₂Te₃ Topological Insulator Thin Films

Persistence of Monoclinic Crystal Structure in 3D Second‐Order Topological Insulator Candidate 1T′‐MoTe₂ Thin Flake Without Structural Phase Transition

The Casimir Effect in Topological Matter

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Tuning the Chern number in quantum anomalous Hall insulators

Cited by 134 publications

References 33 publications

Quantum Oscillations in Ferromagnetic (Sb, V)2Te3 Topological Insulator Thin Films

Quantum Oscillations in Ferromagnetic (Sb, V)2Te3 Topological Insulator Thin Films

Persistence of Monoclinic Crystal Structure in 3D Second‐Order Topological Insulator Candidate 1T′‐MoTe2 Thin Flake Without Structural Phase Transition

The Casimir Effect in Topological Matter

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Quantum Oscillations in Ferromagnetic (Sb, V)₂Te₃ Topological Insulator Thin Films

Quantum Oscillations in Ferromagnetic (Sb, V)₂Te₃ Topological Insulator Thin Films

Persistence of Monoclinic Crystal Structure in 3D Second‐Order Topological Insulator Candidate 1T′‐MoTe₂ Thin Flake Without Structural Phase Transition