Local manifestations of thickness-dependent topology and edge states in the topological magnet 
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Lüpke, Felix; Pham, Anh; Zhao, Yi-Fan; Zhou, Ling-Jie; Lu, Wenchang; Briggs, E. L.; Bernholc, J.; Kolmer, Marek; Teeter, Jacob D.; Ko, Wonhee; Chang, Cui-Zu; Ganesh, Panchapakesan; Li, An‐Ping

doi:10.1103/physrevb.105.035423

Cited by 16 publications

(14 citation statements)

References 59 publications

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“…We applied Hubbard repulsions of U = 3, 3.5, and 4 eV to the Mn 3d states on the same structure optimized with PBE + D3 calculations to assess the effects of uncertainty in U and SOC on our results, independent of the structural degrees of freedom. Using U = 3 ∼ 4 eV is also consistent with the range of values commonly used in previous studies. ,,− …”

Section: Computational Methods and Detailssupporting

confidence: 89%

Procedures for Assessing the Stability of Proposed Topological Materials

Ahn,

Kang,

et al. 2023

J. Phys. Chem. C

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We investigate the stability of MnPb 2 Bi 2 Te 6 (MPBT), which is predicted to be a magnetic topological insulator (TI), using density functional theory calculations. Our analysis includes various measures such as enthalpies of formation, Helmholtz free energies, defect formation energies, and dynamical stability. Our thermodynamic analysis shows that the phonon contribution to the energy gain from finite temperature is estimated to be less than 10 meV/atom, which may not be sufficient to stabilize MPBT at high temperatures, even with the most favorable reactions starting from binaries. While MPBT is generally robust against the formation of various defects, we find that the anti-site defect formation of Mn Pb is the most likely to occur, with a corresponding energy less than 60 meV. This can be attributed to the significant energy cost from compressive strain at the PbTe layer. Our findings suggest that MPBT is on the brink of stability in terms of thermodynamics and defect formation, underscoring the importance of conducting systematic analyses of the stability of proposed TIs, including MPBT, for their practical utilization. This study offers valuable insights into the design and synthesis of desirable magnetic TI materials with robust stabilities.

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Section: Computational Methods and Detailssupporting

confidence: 89%

Procedures for Assessing the Stability of Proposed Topological Materials

Ahn,

Kang,

et al. 2023

J. Phys. Chem. C

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“…[98] Moreover the edge states are gapless for QAHS but gapped for axion insulator states. [150] By growing MBT films with molecular beam epitaxy and characterizing them with STM, Lüpke et al [144] observed the edge states of even and odd layer films and confirmed such prediction. Inset of Figure 7f shows the STM image of the 4 SL-3 SL MBT film grown on epitaxial graphene/SiC substrate.…”

Section: Effect Of Heterogeneities On the Surface States In Magnetic ...mentioning

confidence: 92%

“…f) dI/dV spectra at the 3 SL, 4 SL, and the step edge between them. g) dI/dV spectra at the 4 SL, 5 SL, and the step edge between them (panel (f-g) are reprinted with permission [144]. Copyright 2022, American Physical Society).…”

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confidence: 99%

Understanding Heterogeneities in Quantum Materials

Gai

Puretzky

et al. 2022

Advanced Materials

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of novel quantum materials, devices, and systems and to widespread practical applications in quantum computing, networking, and sensing. However, despite the revolutionary promise, the current approaches to discovering, characterizing, and tailoring quantum materials is largely based on "ideal" systems, meaning materials that are treated by their spatially or temporally averaged states. Real materials, both natural and engineered, are usually heterogeneous, with structural defects, impurities, surfaces, edges, interfaces, and disorder across all spatial and temporal scales.While heterogeneities are often viewed as liabilities within conventional systems, it is the electronic and magnetic structures of these heterogeneities that often define and affect the system's quantum phenomena such as coherence, tunneling, fluctuations, entanglement, and topological effects (Figure 1). Defects consisting of missing atoms in semiconductors, such as diamond and silicon carbide, result in tightly bound individual electrons. [2,3] These single electrons exhibit extraordinarily robust quantum states even at room temperature, where their spins can be entangled with their neighbors and addressed with both optical and microwave electronic techniques. [4,5] The junction states in a superlattice consisting of segments of doped and pristine graphene nanoribbon (GNR) can offer topologicallyprotected spin centers, which form a Heisenberg antiferromagnetic spin ½ chain with tunable exchange interactions. [6][7][8] These spin-entangled states would not exist if there were not heterogeneities in the host materials. It is the heterogeneities that enable the creation of a new family of quantum materials. [9] By understanding the roles of heterogeneities in defining and affecting the properties of quantum states, one can develop protocols that control quantum behaviors so that they could be employed as computational devices within the quantum computing paradigm. Thus, understanding heterogeneities is critical for realizing the potentials of the new quantum revolution.Behind this are the profound insights that have come from the application of microscopy, spectroscopy, and first-principles calculations to the understanding of heterogeneities over the last 30 years. [10] While these have led the way in terms of designing completely new states of quantum matter with great Quantum materials are usually heterogeneous, with structural defects, impurities, surfaces, edges, interfaces, and disorder. These heterogeneities are sometimes viewed as liabilities within conventional systems; however, their electronic and magnetic structures often define and affect the quantum phenomena such as coherence, interaction, entanglement, and topological effects in the host system. Therefore, a critical need is to understand the roles of heterogeneities in order to endow materials with new quantum functions for energy and quantum information science applications. In this article, several representative examples are reviewed on the recent progress in connecting the h...

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“…Particularly, a low carrier concentration due to Fermilevel pinning in the center of the band gap makes it an ideal system to realize QAHE experimentally. Our study also opens up the possibility to utilize the AFM Cr 2 O 3 substrate as a heterostructure with the recently discovered magnetic TI materials with ordered magnetic atoms, such as MnBi 2 Te 4 [52,53] or to grow multilayers achieving higher-order Chern numbers [20]. Also, growing conventional s-wave superconductors on top of this heterostructure should also induce topological superconductivity in these quantized edge-states at the interface.…”

Section: Discussionmentioning

confidence: 92%

Large Gap Quantum Anomalous Hall Effect in a Type-I Heterostructure Between a Magnetically Doped Topological Insulator and Antiferromagnetic Insulator

Pham,

Zhou,

Zhao

et al. 2021

Preprint

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Heterostructures between topological insulators (TI) and magnetic insulators represent a pathway to realize the quantum anomalous Hall effect (QAHE). But major challenges remain, typical heterostructures have weak magnetic exchange interactions across the interface, resulting in small inverted band gaps. Magnetic doping can further increase the band gap due to the additional Zeeman effect, but gaps remain small at low concentrations of magnetic dopants, with higher concentrations resulting in shifting of the Fermi-level, that can render the heterostructure metallic. In addition, chemical bonding across interfaces can lead to imperfect interfaces that might induce metallicity or further lower the gap size. Using density functional theory based systematic screening and investigation of thermodynamic, magnetic and topological properties of heterostructures, we demonstrate that forming a type-I heterostructure between a wide gap antiferromagnetic insulator Cr2O3 and a TI-film, such as Sb2Te3, can lead to pinning of the Fermi-level at the center of the gap, even when magnetically doped. Cr-doping in the heterostructure increases the gap to ∼ 64.5 meV, with a large Zeeman energy from the interfacial Cr dopants, thus overcoming potential metallicity due to band bending effects. By fitting the band-structure around the Fermi-level to a 4-band k.p model Hamiltonian, we show that Cr doped Sb2Te3/Cr2O3 is a Chern insulator with a Chern number C = -1. Transport calculations further show chiral edge-modes localized at the top/bottom of the TI-film to be the dominant current carriers in the material. Our predictions of a large interfacial magnetism due to Cr-dopants, that coupled antiferromagnetically to the AFM substrate is confirmed by our polarised neutron reflectometry measurements on MBE grown Cr doped Sb2Te3/Cr2O3 heterostructures, and is consistent with a positive exchange bias measured in such systems recently. Consequently, Cr doped Sb2Te3/Cr2O3 heterostructure represents a promising platform for the development of functional topological magnetic devices, with high tunability.

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Local manifestations of thickness-dependent topology and edge states in the topological magnet MnBi2Te4

Cited by 16 publications

References 59 publications

Procedures for Assessing the Stability of Proposed Topological Materials

Procedures for Assessing the Stability of Proposed Topological Materials

Understanding Heterogeneities in Quantum Materials

Large Gap Quantum Anomalous Hall Effect in a Type-I Heterostructure Between a Magnetically Doped Topological Insulator and Antiferromagnetic Insulator

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