Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session K19: Developments in Higher-Order Topological Insulators |
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Sponsoring Units: DCMP Chair: Wenjin Luo, University of Colorado Boulder Room: Room 211 |
Tuesday, March 7, 2023 3:00PM - 3:12PM |
K19.00001: Cross-correlated topological response of fragile and higher-order topological states Yuxin Wang, Alexander C Tyner, Pallab Goswami Twisted two-dimensional electronic systems can display various competing ordered states, possessing rich topological properties. Apart from correlated insulators and chiral superconductors, supporting net Chern numbers for occupied states, it is also possible to realize higher-order and fragile topological states. Usually, higher-order and fragile topological states do not support gapless edge modes. In this work, we probe the quantized, topological response of such phases. We identify the precise nature of spin and orbital dependent twisted boundary conditions required for quantized pumping of electric charge. Many d-wave ordered states in particle-hole and particle-particle channels are shown to possess such topological properties. |
Tuesday, March 7, 2023 3:12PM - 3:24PM |
K19.00002: Time-reversal generalization of the Hopf insulator Sunje Kim, Hyeongmuk Lim, Bohm-Jung Yang The Hopf insulator is one of few examples of a topological insulator that can be a trivial insulator by adding trivial bands to either the valence band or the conduction band., i.e., delicate topological insulator. Here, we propose another example of the delicate topological insulator, which is obtained by applying Hopf map to time-reversal invariant systems. We show how to build these time-reversal generalized Hopf insulators mathematically and classify them using integer-valued Hopf invariants. The bulk invariants can be related to the non-trivial topological signature at the surface. Using lattice models, we demonstrate the relation between the bulk topology and rotation symmetry of the system. |
Tuesday, March 7, 2023 3:24PM - 3:36PM |
K19.00003: Z2 Spin Hopf Insulator: Helical Hinge States and Returning Thouless Pump Penghao Zhu, Aris Alexandradinata, Taylor L Hughes We introduce a time-reversal-symmetric analog of the Hopf insulator that we call a spin Hopf insulator. The spin Hopf insulator harbors nontrivial Kane-Mele $_2$ invariants on its surfaces, and is the first example of a nonmagnetic delicate topological insulator with spin-orbit coupling. We show that the Kane-Mele $_2$ topology on the surface is generically unstable, but can be stabilized by the addition of a composition of the particle hole and spatial inversion symmetry. Such a symmetry not only protects the surface $_2$ invariant, but also protects gapless helical hinge states on the spin Hopf insulator. |
Tuesday, March 7, 2023 3:36PM - 3:48PM |
K19.00004: Nanofabrication and Transport Studies of Quasi-one-dimensional Topological Insulators Bismuth Halogenides Zheneng Zhang Bismuth Halogenides Bi4X4 (X = Br, I) is a family of quasi-one-dimensional (1D) topological insulators (TIs) which promise advantages such as multiple cleavage planes, strain-induced phase transitions and hosting of helical hinge modes. Recent scanning tunneling microscope (STM) and angle-resolved photoemission spectroscopy (ARPES) studies show that Bi4Br4 has gapless monolayer step edge and a large bulk gap (~0.2meV) which indicates that it is a promising quantum spin Hall insulator (QSHI) up to room temperature. We are able to exfoliate and fabricate hexagonal boron nitride incapsulated thin layer Bi4Br4 field-effect transistors. In this talk, we will discuss latest transport data as functions of magnetic field and temperature. |
Tuesday, March 7, 2023 3:48PM - 4:00PM |
K19.00005: Bi4X4 (X= Br, I)-Based High-Temperature Quantum Spin Hall Physics Chiho Yoon, Yanfeng Zhou, Hongki Min, Fan Zhang The manifestation of quantum phenomena at room temperatures is a major challenge but also a major goal in physics, and this is particularly true for the quantum spin Hall effect. Here we report the theoretical demonstration of high-temperature quantum spin Hall systems based on Bi4X4 (X= Br, I), a rare higher-order topological insulators identified recently. We further investigate their behavior under external electric field. We also comment on the key experimental studies. |
Tuesday, March 7, 2023 4:00PM - 4:12PM |
K19.00006: Novel Phonon-Based Topological Sensors for Dark Matter Detection Omar A Ashour, Sinead M Griffin Dark matter (DM) has so far evaded direct detection. Next-generation DM searches are stretching to lower masses than weakly interacting massive particles (WIMPs), facilitated by increasing detector sensitivity and new proposals of detection in quantum materials. Quantum materials offer an exciting platform for such low-mass DM detection owing to the match of relevant energy scales and the large number of degrees of freedom that can be exploited for DM coupling. In this work, we propose a novel phonon-based quantum sensing mechanism in topological quantum materials and explore low-mass DM detection as a possible application. Through ab initio density functional theory and GW calculations, we study higher-order topological insulators (HOTI) whose hinge states are protected by inversion and time-reversal symmetries. With antiperovskites as our representative HOTIs, we elucidate the effects of non-equilibrium optical phonons on these materials' bulk, surface, and hinge electronic structures, and further examine DM-phonon coupling via different mediators. |
Tuesday, March 7, 2023 4:12PM - 4:24PM |
K19.00007: Anomalous crystal shapes of topological crystalline insulators and higher-order topological insulators Yutaro Tanaka, Tiantian Zhang, Makio Uwaha, Shuichi Murakami Understanding crystal shapes is a fundamental subject in surface science. It is now well studied how chemical bondings determine crystal shapes via dependence of surface energies on surface orientations. Meanwhile, discoveries of topological materials have led us to a new paradigm in surface science, and one can expect that topological surface states may affect surface energies and crystal facets in an unconventional way. Here we show that the surface energy of glide-symmetric topological crystalline insulators (TCI) depends on the surface orientation in a singular way via the parity of the Miller index [1]. This singular surface energy of the TCI affects equilibrium crystal shapes, resulting in emergence of unique crystal facets of the TCI [1]. This singular dependence of the topological surface states is unique to the TCI protected by the glide symmetry in contrast to a TCI protected by a mirror symmetry. In addition, we study crystal shapes of higher-order topological insulators. We show that when a topological insulator transforms into a higher-order topological insulator by adding a magnetic field, the crystal shape changes in a peculiar way. |
Tuesday, March 7, 2023 4:24PM - 4:36PM |
K19.00008: Bulk-boundary correspondence in 2D mirror-symmetric higher-order topological insulators Babak Seradjeh, Suman Aich We study the higher-order bulk-boundary correspondence in a family of generalized models with extended hopping terms and anti-commuting mirror symmetries. Specifically, we study the symmetry structure of Wilson loops for this class of models and define a set of bulk Z invariants that characterize their topology. We illustrate the bulk-boundary correspondence by showing these invariants match the number of corner states in an open geometry. We also show that corner bound states are robust and their number is correctly captured by our bulk Z invariants in the presence of chiral symmetry breaking terms in the Hamiltonian. |
Tuesday, March 7, 2023 4:36PM - 4:48PM |
K19.00009: Magnetic wallpaper Dirac fermions and topological magnetic Dirac insulators Yoonseok Hwang, Yuting Qian, Junha Kang, Jehyun Lee, Hong Chul Choi, Bohm-Jung Yang Topological crystalline insulators (TCIs) can host surface states whose anomalous band structure inherits the characteristics of the crystalline symmetry that protects the bulk topology. Especially, in magnetic crystals, the diversity of magnetic crystalline symmetries indicates the potential to achieve novel magnetic TCIs with distinct surface characteristics. Here, we propose a new type of magnetic TCI, coined the topological magnetic Dirac insulator (TMDI), whose two-dimensional (2D) surface hosts fourfold-degenerate Dirac fermions protected by either p'c4mm or p4'g'm magnetic wallpaper groups (MWGs). The bulk band topology of TMDIs is protected by diagonal mirror symmetries, which give the chiral dispersion of surface Dirac fermions and mirror-protected hinge modes. We also propose a class of candidate materials for TMDIs including Nd4Te8Cl4O20 and DyB4 based on first-principle calculations, and construct a general scheme to search TMDIs using the space group symmetry of paramagnetic parent states. We believe that our theoretical discovery of TMDIs and their anomalous surface Dirac fermions would facilitate the future research of new magnetic TCIs and illustrate a distinct way to achieve anomalous surface states in magnetic crystals. |
Tuesday, March 7, 2023 4:48PM - 5:00PM |
K19.00010: Ballistic 1D channels in multilayer-WTe2 Josephson junctions. Xavier Ballu, Ziwei Dou, Alexandre Bernard, Raphaëlle Delagrange, Robert Cava, Leslie M Schoop, Hélène Bouchiat, Richard Deblock, Sophie Guéron, Meydi Ferrier WTe2, a transition metal dichalcogenide, is predicted to have striking topological properties that combine type II Weyl semimetal character with second-order 3D topological insulator (SOTI) character. SOTIs are characterized by topologically protected (insensitive to disorder) helical 1D states at their hinges. 1D states located at certain edges of multilayer WTe2 have indeed been demonstrated in Josephson interferometry experiments. However, their ballistic nature was not tested. We have designed a WTe2-based Superconducting Quantum Interference Device (SQUID) in which the supercurrent through one edge of the crystal interferes with the supercurrent far from the edge. The critical current of this asymmetric SQUID yields the supercurrent-versus-phase relation of the edge states. Its sawtooth shape is a tell-tale sign that the supercurrent through the edge flows ballistically over 600 nm (which is ten times the estimated normal state mean free path). This is due to the SOTI character of WTe2. |
Tuesday, March 7, 2023 5:00PM - 5:12PM |
K19.00011: Evidence of a topological edge state in a Rashba compound Md. Shafayat Hossain, Yuxiao Jiang, Qi Zhang, Maksim Litskevich, Zijia Cheng, Zahir Muhammad, Frank Schindler, Tyler A Cochran, Xian Yang, Jiaxin Yin, Titus Neupert, Weisheg Zhao, Zahid M Hasan The presence of a gapless edge state within a bulk energy gap, namely the bulk-boundary correspondence, is a hallmark of topology. Using scanning tunneling microscopy, we uncover such an edge state in a Rashba compound containing a Rashba-split surface state. In an atomically resolved surface, we observe a small gap near the Fermi level. On the other hand, a monolayer atomic step edge features an in-gap, gapless edge state. We argue the topological nature of the edge state based on two experimental findings: |
Tuesday, March 7, 2023 5:12PM - 5:24PM |
K19.00012: Green's function approach to interacting higher-order topological insulators Heqiu Li, Hae-Young Kee, Yong-Baek Kim The Bloch wave functions have been playing a crucial role in the diagnosis of topological phases in noninteracting systems. However, the Bloch waves are no longer applicable in the presence of finite Coulomb interaction and alternative approaches are needed to identify the topological indices. In this paper, we focus on three-dimensional higher-order topological insulators protected by C4T symmetry and show that the topological index can be computed through eigenstates of inverse Green's function at zero frequency. If there is an additional S4 rotoinversion symmetry, the topological index P3 can be determined by eigenvalues of S4 at high-symmetry momenta, similar to the Fu-Kane parity criterion. We verify this method using many-body exact diagonalization in higher-order topological insulators with interaction. We also discuss the realization of this higher-order topological phase in tetragonal lattice structure with C4T-preserving magnetic order. Finally, we discuss the boundary conditions necessary for the hinge states to emerge and show that these hinge states exist even when the boundary is smooth and without a sharp hinge. |
Tuesday, March 7, 2023 5:24PM - 5:36PM |
K19.00013: Spin-Resolved Topology, Partial Axion Angles, and Surface Anomalies in Time-Reversal-Invariant Insulators: Numerical Analysis Techniques Kuan-Sen Lin, Yoonseok Hwang, Giandomenico Palumbo, Zhaopeng Guo, Jeremy Blackburn, Daniel P Shoemaker, Fahad Mahmood, Zhijun Wang, Gregory A Fiete, Benjamin J Wieder, Barry Bradlyn 3D higher-order topological crystalline insulators (HOTIs) exhibit 1D hinge states whose configuration depends on the details of the sample termination. In this work, we identify sample-independent bulk experimental signatures of time-reversal- (T-) invariant (helical) HOTIs. We develop numerical techniques to characterize the bulk topological properties of 2D and 3D insulators: (nested) spin-resolved Wilson loops, position-space Chern numbers (which we relate to spin-resolved layer constructions), and spin-resolved entanglement spectra. We introduce spin-resolved topological phases along with these numerical techniques. We find that helical HOTIs realize one of three spin-resolved phases: (i) 3D quantum spin Hall insulators, (ii) spin-Weyl semimetals with gapless spin spectra, and (iii) T-doubled axion insulators with nontrivial partial axion angles indicative of a 3D spin-magnetoelectric bulk response and whose surfaces realize anomalous halves of a 2D topological insulator. We provide experimental signatures of each of these spin-resolved phases. We also use ab-initio calculations to demonstrate that the candidate HOTI β-MoTe2 realizes a spin-Weyl semimetal state. Lastly, we consider the relationship between symmetry and U(1) magnetic flux insertion in helical HOTIs. |
Tuesday, March 7, 2023 5:36PM - 5:48PM |
K19.00014: Bulk and Surface Theories for Helical Higher-Order Topological Insulators Benjamin J Wieder, Giandomenico Palumbo, Kuan-Sen Lin, Yoonseok Hwang, Zhaopeng Guo, Fahad Mahmood, Zhijun Wang, Senthil Todadri, Gregory A Fiete, Barry Bradlyn 3D higher-order topological crystalline insulators (HOTIs) exhibit intrinsic 1D hinge modes in highly symmetric model geometries. Away from the unrealistic limit of perfect global crystal symmetry, topological phases can still be described by continuum field and response theories. Magnetic HOTIs with chiral hinge modes have recently been recognized to carry bulk nontrivial axion angles θ=π, clarifying their response. But for HOTIs with helical hinge modes, the analogous bulk and surface theories are not yet known. This significantly constrains currently available experimental signatures, despite the wealth of accessible material candidates including bismuth, MoTe2, WTe2, and BiBr. In this talk, we first use the recently-developed concept of spin-resolved topology to analyze helical HOTIs with (weakly) broken Sz symmetry, finding that they carry quantized “partial” axion angles, which lead to anomalous surface half quantum spin Hall states and a bulk spin-magnetoelectric response. We then use dimensional reduction and the insertion of magnetic flux and monopoles to theoretically characterize helical HOTIs with arbitrarily strong spin-orbit coupling. |
Tuesday, March 7, 2023 5:48PM - 6:00PM |
K19.00015: Magnetic Quadrupole Moment in Higher-Order Topological Phases Jacopo Gliozzi, Mao Lin, Taylor L Hughes We study orbital magnetic quadrupole moment (MQM) in three dimensional higher-order topological phases. Much like electric quadrupole moment, which is associated with a charge response on the boundaries of a finite sample, the MQM manifests as surface-localized magnetization and hinge currents. The surface magnetization is anomalous in the sense that it is generally not equal to the hinge current surrounding the same surface. This mismatch is precisely quantified by the bulk MQM. We derive a quantum mechanical formula for the layer-resolved magnetization in slab geometries and use it to define the MQM of systems with gapped boundaries. The formalism is then applied to several higher-order topological phases, and we show that the MQM can distinguish some intrinsic and boundary-obstructed higher-order topological insulators. Our work allows for new studies of electromagnetic responses in higher-order topological phases and beyond.
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