Topological Insulator Materials

Ando, Yoichi

doi:10.7566/jpsj.82.102001

Cited by 1,664 publications

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“…σ bulk σ SS , the total thermopower will not exceed the bulk limit considerably, yielding S tot ≈ S ∞ . 2 We note that there is a difference of S bulk and S ∞ , which are the bulk contribution to a thin film and the contribution of a perfect infinite bulk, respectively. However, S bulk = S ∞ is used in this estimation and is valid for qualitative discussions.…”

Section: Theoretical Resultsmentioning

confidence: 91%

“…The Sb 2 Te 3 thin films were grown on silicon wafers with a top layer of 300 nm SiO 2 via Atomic Layer Deposition (ALD) at substrate temperatures of 353 K. (Et 3 Si) 2 Te and SbCl 3 were used as precursors at source temperatures of 350 K and 328 K, respectively. 34 For the transport measurements the Sb 2 Te 3 thin films were deposited on a lithographically pre-patterned Hall bar, which was defined via laser beam lithography and subsequent developing of the exposed photoresist.…”

Section: Methodsmentioning

confidence: 99%

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Impact of the Topological Surface State on the Thermoelectric Transport in Sb₂Te₃ Thin Films

et al. 2015

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Ab initio electronic structure calculations based on density functional theory and tight-binding methods for the thermoelectric properties of ptype Sb 2 Te 3 films are presented. The thicknessdependent electrical conductivity and the thermopower are computed in the diffusive limit of transport based on the Boltzmann equation. Contributions of the bulk and the surface to the transport coefficients are separated which enables to identify a clear impact of the topological surface state on the thermoelectric properties. By tuning the charge carrier concentration, a crossover between a surface-state-dominant and a FuchsSondheimer transport regime is achieved. The calculations are corroborated by thermoelectric transport measurements on Sb 2 Te 3 films grown by atomic layer deposition.Almost all proposed three-dimensional (3D) Z 2 topological insulators (TIs) 1,2 are efficient thermoelectric materials. That is not by coincidence, since the link between an efficient thermoelectric * To whom correspondence should be addressed † Institute of Physics, Martin Luther University HalleWittenberg, D-06099 Halle, Germany ‡ Institute of Nanostructure and Solid State Physics, Universität Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany ¶ Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle, Germany material and the topological character is the inverted band gap. 3,4 The last is due to spin-orbit coupling which switches parity of the bands and leads, if strong enough, to narrow band gaps which are favourable for efficient room-temperature thermoelectrics. Usually strong spin-orbit coupling is mediated by heavy elements which in turn also tend to reduce the material's lattice thermal conductivity, another requirement for desirable thermoelectrics.In the early 90's, Hicks and Dresselhaus 5,6 proposed the concept of low-dimensionality to increase further the thermoelectric efficiency; primarily in thin films, the thermopower S should be enlarged. However, in contrast to previous theoretical model calculations, 7,8 decreased values of S were found experimentally 9-11 for Bi 2 Te 3 and Sb 2 Te 3 thin films and were recently corroborated by both model 12,13 and ab initio calculations 4 of our groups.Thus, to resolve this discrepancy, the potential impact of the surface state (SS) of TIs on thermoelectricity needs to be investigated in more detail. In this Letter, we present ab initio calculations and transport measurements of the thermoelectric properties of Sb 2 Te 3 films at varying thickness, temperature and charge carrier concentration. (1/ cm)(g) Theoretical resultsIn the following, we discuss the doping-and temperature-dependent electrical conductivity and thermopower, as shown in Fig. 1, exemplary for a Sb 2 Te 3 film thickness of 18 quintuple-layer (QL), i.e. about 18 nm. A discussion of films with other thicknesses is given in the supplemental material. 14 The converged electronic structure results serve as input to obtain the thermoelectric transport properties at temperature T and fixed extri...

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Section: Theoretical Resultsmentioning

confidence: 91%

Section: Methodsmentioning

confidence: 99%

Impact of the Topological Surface State on the Thermoelectric Transport in Sb₂Te₃ Thin Films

et al. 2015

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“…More recently, the research on topological states has been extended to three-dimensional (3D) semimetal systems. [8][9][10][11][12] These systems could demonstrate many fascinating phenomena, such as Weyl fermion quantum transport and various Hall effects, [13][14][15][16] consequently become the rising stars of the field. Up to now, three kinds of topological semimetals have been discovered, i.e., 3D Dirac semimetal (DSM), 12,[17][18][19][20][21] Weyl semimetal (WSM), 8,9,22,23 and node-line semimetal (NLS).…”

Section: Introductionmentioning

confidence: 99%

CaTe: a new topological node-line and Dirac semimetal

Du¹,

Tang²,

Wang³

et al. 2017

npj Quant Mater

114

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Combining first-principles calculations and effective model analysis, we predict that CaTe is a topological node-line semimetal in the absence of the spin-orbit coupling. Using a slab model, we obtain the nearly flat drumhead surface state near the Fermi level. When the spin-orbit coupling is included, three node lines will evolve into a pair of Dirac points along the M−R line. These Dirac points are robust and protected by the C 4 rotation symmetry. Once this crystal symmetry is broken, the Dirac points will be eliminated, and the system becomes a strong topological insulator.npj Quantum Materials (2017) 2:3 ; doi:10.1038/s41535-016-0005-4 INTRODUCTIONTopological insulator (TI) has attracted broad interest in the past 10 years. [1][2][3][4][5][6][7] The unique property of TI is that it is an insulator in the bulk but has exotic metallic surface states due to the topological order. More recently, the research on topological states has been extended to three-dimensional (3D) semimetal systems. [8][9][10][11][12] These systems could demonstrate many fascinating phenomena, such as Weyl fermion quantum transport and various Hall effects, [13][14][15][16] consequently become the rising stars of the field. Up to now, three kinds of topological semimetals have been discovered, i.e., 3D Dirac semimetal (DSM), 12,[17][18][19][20][21] Weyl semimetal (WSM), 8,9,22,23 and node-line semimetal (NLS). [24][25][26][27][28][29] The 3D DSM has four-fold degeneracy point, which can be viewed as the kiss of two Weyl fermions with opposite chiralities in the Brillouin zone (BZ). Protected by the crystal symmetry and time reversal symmetry, 3D DSMs can be robust against external perturbations. Several materials have been theoretically predicted to be 3D DSMs 12,17-21 and some of them have already been confirmed by experiments. [30][31][32][33] If one breaks the time reversal symmetry 8,22,23,34 or the inversion symmetry, 35-38 the 3D DSM will evolve into WSM. Very recently, the predictions about WSM state in TaAs family 37,38 have been confirmed experimentally. [39][40][41][42] Unlike DSM and WSM whose band crossing points distribute at separate k points in the BZ, for a NLS the crossing points around the Fermi level form a closed loop. Several compounds have been proposed as NLSs, including Mackay-Terrones crystals, 25 Bernal graphite, 43 hyperhoneycomb lattices, 44 and antiperovskite Cu 3 PdN 26,27 and Cu 3 NZn. 27 In the absence of spin-orbit coupling (SOC), time reversal symmetry together with inversion or mirror symmetry will guarantee the occurrence of node line in 3D BZ for systems with band inversion. [25][26][27]37,45,46 Same with TI and WSM, NLS also has a characteristic surface state, namely, drumhead-like state. 24-29 Such a 2D flat band surface state may become a route to achieve high temperature superconductivity. 47,48 As a result, it is of great impetus to search new NLS.In this study, based on first-principles calculations and effective model analysis, we propose that CaTe in CsCl-type structure is a NLS with drumhea...

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“…Recently, topological insulators have received significant research attention in solid-state physics [1][2][3]. Topological insulators have metallic surface states, which are described by the Dirac Hamiltonian.…”

Section: Introductionmentioning

confidence: 99%

First-Principles Study of Topological InsulatorsA₂B₃(A= Bi and Sb, andB= O, S, Se, and Te)

Kato¹,

Kotaka²,

Ishii³

2015

Proceedings of Computational Science Workshop 2014 (CSW2014)

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We investigate the electronic states of rhombohedral A 2 B 3 using first-principles calculations, where A = Bi and Sb, and B = O, S, Se, and Te. The topological states of insulators are predicted from Z 2 topological invariants. We reveal topological phase diagrams of Bi 2 Te 3 and Bi 2 Se 3 in the space of the internal parameters. We find topological phase transitions in Bi 2 Te 3 and Bi 2 Se 3 . The isostructural hypothetical materials A 2 B 3 (where A=Bi and Sb and B=S and O) are also investigated. We find that non-trivial topological phases are realized in Bi 2 S 3 due to the lattice strain.

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Topological Insulator Materials

Cited by 1,664 publications

References 302 publications

Impact of the Topological Surface State on the Thermoelectric Transport in Sb₂Te₃ Thin Films

Impact of the Topological Surface State on the Thermoelectric Transport in Sb₂Te₃ Thin Films

CaTe: a new topological node-line and Dirac semimetal

First-Principles Study of Topological InsulatorsA₂B₃(A= Bi and Sb, andB= O, S, Se, and Te)

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Topological Insulator Materials

Cited by 1,664 publications

References 302 publications

Impact of the Topological Surface State on the Thermoelectric Transport in Sb2Te3 Thin Films

Impact of the Topological Surface State on the Thermoelectric Transport in Sb2Te3 Thin Films

CaTe: a new topological node-line and Dirac semimetal

First-Principles Study of Topological InsulatorsA2B3(A= Bi and Sb, andB= O, S, Se, and Te)

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Impact of the Topological Surface State on the Thermoelectric Transport in Sb₂Te₃ Thin Films

Impact of the Topological Surface State on the Thermoelectric Transport in Sb₂Te₃ Thin Films

First-Principles Study of Topological InsulatorsA₂B₃(A= Bi and Sb, andB= O, S, Se, and Te)