Unconventional Materials: the mismatch between electronic charge centers and atomic positions

Gao, Jiacheng; Qian, Yuting; Jia, Huaxian; Guo, Zhaopeng; Fang, Zhong; Liu, Miao; Weng, Hongming; Wang, Zhijun

doi:10.48550/arxiv.2106.08035

Cited by 6 publications

(6 citation statements)

References 61 publications

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“…The implementation of RSIs in searching for 3D obstructed atomic insulators and their applications were originally presented on the APS March Meeting of 2021 [62]. During the preparation of this manuscript, one work appeared on arXiv [63] where examples of OAI are presented.…”

Section: Acknowledgmentsmentioning

confidence: 99%

Three-Dimensional Real Space Invariants, Obstructed Atomic Insulators and A New Principle for Active Catalytic Sites

Xu¹,

Elcoro²,

Li³

et al. 2021

Preprint

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Topologically trivial insulators come in two kinds: atomic, where the Wannier charge centers (WCCs) are localized on the atoms, and obstructed atomic, where the WCCs are located away from the atoms. The latter, which can exhibit interesting surface states and possibly have much larger band gaps than the topological insulators, have so far not been classified in three-dimensional (3D) crystalline materials. In this paper, we developed the 3D real space invariants (RSIs) for the 1,651 Shubnikov space groups with the spin-orbit coupling and provide the full classification of 3D obstructed atomic insulators (OAIs) by the RSIs. We then apply the theory to the entire database of materials on the Topological Quantum Chemistry website and Topological Magnetic Materials website, obtaining all the paramagnetic and magnetic OAIs so far existing in nature. We find that, out of the 34,013 paramagnetic and 296 magnetic topologically trivial insulators, there are 3,383 paramagnetic and 30 magnetic OAIs. All of them present a filling anomaly under certain open-boundary conditions and exhibit obstructed surface states (OSSs). We then derive the Miller indices of the cleavage planes which show the OSSs for all the OAIs and pick some of the best examples with large band gap to showcase their OSSs. We further refine the atomic insulator concept to obtain the orbital-selected OAIs (OOAIs), where the WCC of the system is located at a Wyckoff position occupied by an atom but forms a symmetric representation (orbital) that does not belong to the outer-shell electrons of the given atom. In such a way, we obtain a further 121 OOAIs. Furthermore, we analyze the catalytic properties of one of the OAIs in a "proof of principle" experiment. The surface of a high-performance heterogeneous catalyst is characterized by high stability, good electrical conductivity, and high charge carrier density near the Fermi level. These are also characteristic properties of the OSSs. By using a high-quality, single crystal of 2H-MoS 2 , that has well-defined surfaces, as a hydrogen evolution catalyst, we directly proved that the catalytic activities arise from the surfaces with OSSs, which is consistent with previous results based on electronic-structure calculations. Additional potential applications of the 3D RSIs and OAIs in, for example, electrochemistry, asymmetric catalysis, superconductivity and Josephson diode will be discussed.

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Section: Acknowledgmentsmentioning

confidence: 99%

Three-Dimensional Real Space Invariants, Obstructed Atomic Insulators and A New Principle for Active Catalytic Sites

Xu¹,

Elcoro²,

Li³

et al. 2021

Preprint

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“…Importantly, when the cleavage termination cuts through those electron-filled AUWPs (namely, OWCCs) in an OAI, the metallic surface states will emerge. This crucial feature makes OAIs be potential candidates for superconductivity and catalysis [46][47][48][49][50] . To date, OAIs including 3,383 paramagnetic and 30 magnetic materials are reported in threedimensional (3D) materials 45,46 .…”

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confidence: 99%

Two-dimensional Obstructed Atomic Insulators with Fractional Corner Charge in MA$_2$Z$_4$ Family

Wang¹,

Jiang²,

Liu³

et al. 2022

Preprint

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According to topological quantum chemistry, a class of electronic materials have been called obstructed atomic insulators (OAIs), in which a portion of valence electrons necessarily have their centers located on some empty Wyckoff positions without atoms occupation in the lattice. The obstruction of centering these electrons coinciding with their host atoms is nontrivial and results in metallic boundary states when the boundary is properly cut. Here, on basis of first-principles calculations in combination with topological quantum chemistry analysis, we propose two dimensional MA2Z4 (M = Cr, Mo and W; A = Si and Ge, Z = N, P and As) monolayer family are all OAIs. A typical case is the recently synthesized MoSi2N4. Although it is a topological trivial insulator with the occupied electronic states being integer combination of elementary band representations, it has valence electrons centering empty Wyckoff positions. It exhibits unique OAI-induced metallic edge states along the (1 10) edge of MoSi2N4 monolayer and the in-gap corner states at three vertices of certain hexagonal nanodisk samples respecting C3 rotation symmetry. The readily synthesized MoSi2N4 is quite stable and has a large bulk band gap of 1.94 eV, which makes the identification of these edge and corner states most possible for experimental clarification.

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“…Note, however, that although the BRs of As and Sb can be decomposed into linear combinations of EBRs, these cannot be expressed as linear combinations of atomic band representations (aBRs). Therefore, they belong to obstructed atomic insulators [28,29]. Consider As 1−x Sb x with the doping from x = 1 to x = 0, equivalent to annihilating the two pairs of DPs in Sb, it can easily reach the conclusion that As is an obstructed atomic insulator according to the reference [30].…”

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confidence: 99%

High Spin-Chern-Number Insulator in $α$-Antimonene with a Hidden Topological Phase

Wang¹,

Zhou²,

Lin³

et al. 2022

Preprint

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In investigating the topological electronic structures of monolayer α-phase group V elements, we uncover a new topological phase, which is invisible in the symmetry-based topological quantum chemistry (TQC) as well as symmetry indicators (SIs). Since α phase As and Sb share the same band representations at high-symmetry points, they are both trivial insulators in terms of TQC and SIs. We demonstrate, however, that there is a topological phase transition between As and Sb that involves a band-gap closing at two k-points on the high-symmetry X-Γ-X line. In the absence of spin-orbit coupling (SOC), As is a trivial insulator, while Sb is a Dirac semimetal with four Dirac points (DPs) located away from the high-symmetry lines. Inclusion of Sz-conserved SOC gaps out the Dirac points and induces a nontrivial Berry curvature and drives Sb into a high spin Chern number topological phase. The band structure of α-Bi differs from that of Sb by a band inversion at Γ, transforming Bi into a Z2 topological insulator. Our study shows that quantized spin Hall conductivity can serve as a topological invariant beyond Z2 for characterizing topological phases.

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Unconventional Materials: the mismatch between electronic charge centers and atomic positions

Cited by 6 publications

References 61 publications

Three-Dimensional Real Space Invariants, Obstructed Atomic Insulators and A New Principle for Active Catalytic Sites

Three-Dimensional Real Space Invariants, Obstructed Atomic Insulators and A New Principle for Active Catalytic Sites

Two-dimensional Obstructed Atomic Insulators with Fractional Corner Charge in MA$_2$Z$_4$ Family

High Spin-Chern-Number Insulator in $α$-Antimonene with a Hidden Topological Phase

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