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 D23: Advances in Probing and Designing Topological Materials: Theory and Experiment |
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Sponsoring Units: DCMP Chair: Clifford Hicks, University of Birmingham Room: Room 215 |
Monday, March 6, 2023 3:00PM - 3:12PM |
D23.00001: Surface transport anomalies of quasi-one-dimensional weak topological insulators Tianyi Xu, Fengcheng Wu, Fan Zhang Prototypical weak topological insulators (WTI) have been theoretically predicted to be realized in quasi-one-dimensional materials Bi4X4 (X = Br, I) [PRL 116, 066801 (2016)] and then experimentally confirmed via ARPES [PRX 11, 031042 (2021) & Nature 566, 518 (2019)]. The unique surface states of such a WTI have two entangled Dirac cones with strong anisotropy. We study theoretically the integer quantum Hall effect of such WTI surface states and show the important roles played by the special geometry, symmetry, topology, and their interplay in Bi4X4. We also predict prominent signatures in transport experiments. |
Monday, March 6, 2023 3:12PM - 3:24PM |
D23.00002: Even-odd interatomic, interorbital hybridization as a source of topological insulators Nassim Derriche, George A Sawatzky We present a novel set of systems which are topological insulators, namely materials characterized by interatomic, interorbital hybridization between neighboring s and p orbitals.. We study a one-dimensional chain of alkali metal atoms as the prototypical example of such a system to demonstrate the key characteristics of this set of materials, including the topologically-protected edge states they exhibit and the symmetries protecting them. We also show that if s-s and p-p hopping are tuned to the same amplitude, particle-hole symmetry is attained and the system is topologically identical to the Kitaev chain with the interatomic s-p hopping terms taking the place of the superconducting pairing, albeit hosting s-p mixed electrons instead of electron-hole (Majonara) fermions. Considering that the even-odd symmetry of the s-p mixing is the essential ingredient that allows for the realization of such properties, materials that involve higher-angular momentum orbitals such as d states can also possess the topological properties we describe. We also discuss two-dimensional systems and experimental realization. |
Monday, March 6, 2023 3:24PM - 3:36PM |
D23.00003: Experimental observation of topological phases in a longitudinal SSH mechanical model. Juan M Merlo-Ramirez, Madeleine Carhart The SSH model [1] is one of the most important theoretical approaches to the study of topological properties of one-dimensional materials. We present the implementation of a mechanical topological insulator based on the SSH model. By modulating the elastic constant of a set of plastic slabs, we were able to demonstrate the topological phase transitions when the appropriate conditions were met under longitudinal modes. Our work generalizes the recently discovered universality of the critical exponents in a mechanical topological insulator when transverse waves were used [2]. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D23.00004: Bismuth antiphase domain wall: A three-dimensional manifestation of the Su-Schrieffer-Heeger model Jinwoong Kim, Cheng-Yi Huang, Hsin Lin, David Vanderbilt, Nicholas Kioussis The Su, Schrieffer, and Heeger (SSH) model, describing the soliton excitations in polyacetylene due to the formation of antiphase domain walls (DW) from the alternating bond pattern, has served as a paradigmatic example of one-dimensional (1D) chiral topological insulators. While the SSH model has been realized in photonic and plasmonic systems, there have been limited analogues in three-dimensional (3D) electronic systems, especially regarding the formation of antiphase DWs. Here, we propose that pristine bulk Bi, in which the dimerization of (111) atomic layers renders alternating covalent and Van der Waals bonding within and between successive (111) bilayers, respectively, serves as a 3D analogue of the SSH model. First, we confirm that the two dimerized Bi structures belong to different Zak phases of 0 and π by considering the parity eigenvalues and Wannier charge centers, while the previously reported bulk topological phases of Bi remain invariant under the dimerization reversal. Next, we demonstrate the existence of topologically non-trivial (111) and trivial (11-2) DWs in which the number of in-gap DW states (ignoring spin) is odd and even respectively, and show how this controls the interlinking of the Zak phases of the two adjacent domains. Finally, we derive general criteria specifying when a DW of arbitrary orientation exhibits a π Zak phase based on the flip of parity eigenvalues. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D23.00005: Structure-property relationships of the multi-orbital honeycomb lattice Caolan John, Joseph G Checkelsky The honeycomb lattice has long been a powerful toy model for analyzing the relationship between lattice geometry and topological phases of matter, as has been extensively studied in the form of graphene [1]. Unlike the prototypical carbon-based compound, heavier honeycomb analogs have recently emerged as a promising platform for accessing topological physics at elevated temperature scales stemming from their multi-orbital character. Here we will describe the structure-property relationships inherent in px/py honeycomb materials, emphasizing the interplay between the lattice and quantum geometries. We will also discuss recent progress in realizing material structures that may enable the study of these exotic systems. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D23.00006: Perfectly localized Majorana corner modes in fermionic lattices Prathyush P Poduval, Thomas L Schmidt, Andreas O Haller The conducting bulk and surface modes of topological systems can be gapped out, resulting in systems which are commonly referred to as higher order topological insulators (HOTIs). Focusing on examples of Majorana zero modes on the corners of a two-dimensional system, we introduce a method to find parameter regions where the Majorana modes are perfectly localised on a single site, with zero correlation length. Such a limit allows us to study the dimerisation structure of the sparse bulk Hamiltonian that results in the higher order topology of the system. Furthermore, such limits typically feature a feasible analytical understanding of the system's energy scales. Based on the dimerisation structure we extract from the 2D model, we identify a more general stacking procedure to construct Majorana zero modes in arbitrary corners of a $d$ - dimensional hypercube, which we demonstrate explicitly in 3D. Our construction requires no inherent crystalline symmetries, and the Majorana corner modes are protected by the particle-hole symmetry of edge Hamiltonians, inherited from the BdG Hamiltonians of the bulk. Edited |
Monday, March 6, 2023 4:12PM - 4:24PM Author not Attending |
D23.00007: Zeeman field induced midgap mode in two-dimensional node line semimetal Yuanjun JIN, Xingyu Yue, Guoqing Chang Two-dimensional node line semimetals protected by nonsymmorphic and parity-time symmetries are robust against weak perturbations. Since the topological invariant is not well defined, there is no edge states in the two-dimensional node line semimetal, which hinders the electronic device application. In this talk, we show that by introducing in-plane Zeeman field the two-dimensional node line semimetal can open an energy gap and generate midgap mode separated from bulk bands. The midgap state is protected by Berry phase π and well localized in each edge with fractional charge e/2. We also discuss the magnetic flux effects in such node line semimetal. Under magnetic flux field, the node line is split into one pair of Dirac points in the boundary of Brillouin zone. The location of the Dirac points is determined by the gauge chosen for the vector potential. Finally, we discuss the experimental realization of our model. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D23.00008: Surface states in HgTe and α-Sn semimetals in various topological regimes Alexander Khaetskii, Vitaly Golovach, Arnold Kiefer We revisit theoretically the problem of surface states in semiconductors with inverted-band structures, such as α-Sn and HgTe. We unravel the confusion that arose over the past decade regarding the origin of the surface states, their topological nature, and the role of strain. Within simple and exactly solvable models, we reconcile different solutions found in the 1980s with the results obtained from modern-day numerical simulations. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D23.00009: Interplay between anisotropic spin texture and large gap topological insulating phases in functionalized MXenes Aniceto B Maghirang Massive attention has been given to two-dimensional (2D) MXenes due to their predicted topological phase and promising diverse applications. Using first-principles with hybrid functional calculations, we systematically conducted an extensive study on M2C (M = Mo, or W) in 1T and 2H structures with various surface terminations T2 (T = H, O, OH, F, Cl, Br, or I). Pristine Mo2C and W2C compounds are in the 2H phase. Upon functionalization of H, O, OH and F, they retain the 2H structure, whereas Cl, Br, and I functionalization, the structures transform to 1T phase. Notably, M2CO2 are found to be 2D topological insulators (TIs) with sizable nontrivial bandgaps as large as 666 meV. Interestingly, 2H M2CO2 exhibits not only large-gapped Zeeman-type spin splitting at K-point but also anisotropic Rashba spin splitting at Γ-point. The successful synthesis of pristine Mo2C and our theoretical study pave a path for future applications of MXene-based 2D TIs. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D23.00010: Dynamical stability and electron-phonon interactions in topologically protected conducting channel of atomically thin Bi (111) Enamul Haque, Yuefeng Yin, Nikhil V Medhekar Two-dimensional topological insulators possess a single conducting channel embedded inside the insulating bulk surface bandgap, which can be complicated to realize in practical devices due to electron-phonon interactions (EPI) at finite temperatures. Using single bilayer Bi (111) (SBB) and the first-principles method, we find that imaginary phonon modes exist in the native edges, suggesting dynamical instability. We also find that hydrogen passivation-induced sp-hybridization increases spin-orbit coupling (SOC) in the edge atoms. The passivation can entirely remove the imaginary phonon modes of the zigzag edge due to an equal increase of the SOC. In contrast, it cannot entirely remove the imaginary phonon modes of the armchair edge due to the unequal growth of SOC. While the electronic edge states of the native edges don't exhibit a linear dispersion, the passivation can bring linear dispersion. We show that the EPI strongly depend on the edge states dispersion. Particularly, when the dispersion of the topological edge electronic states becomes more linear, the EPI gets negligibly weaker and vice versa. Additionally, we find that the surface phonons have nonzero topological invariant, suggesting the existence of topological phononic edge states in SBB. |
Monday, March 6, 2023 5:00PM - 5:12PM |
D23.00011: Magnetic dilution effect and topological phase transitions in (Mn1-xPbx)Bi2Te4 Tiema Qian As the first intrinsic antiferromagnetic (AFM) topological insulator (TI), MnBi2Te4 has provided a material platform to realize various emergent phenomena arising from the interplay of magnetism and band topology, including quantum anomalous Hall effect. In this talk, I will present our investigation on (Mn1-xPbx)Bi2Te4 (0≤x≤0.82) single crystals that reveal the magnetic dilution effect on the magnetism and band topology in MnBi2Te4. With increasing x, Néel temperature decreases linearly while a slight decrease of the interlayer plane-plane antiferromagnetic exchange interaction and a monotonic decrease of the magnetic anisotropy are revealed. We attribute these observations to the dilution of magnetic ions and enlarging unit cell. The dilution of Mn atoms also leads to the decrease of the MnBi antisites, reducing the magnetic inhomogenuity that is known to be detrimental to the realization of the quantum anomalous Hall effect. Furthermore, our first-principles calculations reveal that the band inversion in the two end materials, MnBi2Te4 and PbBi2Te4, occurs at the Γ and Z point, respectively, while two gapless points appear at x = 0.44 and x = 0.66, suggesting possible topological phase transitions with doping. |
Monday, March 6, 2023 5:12PM - 5:24PM |
D23.00012: Quantum spin Hall insulating phase and van Hove singularities in Zintl single-quintuple-layer AM2X2 (A = Ca, Sr, or Ba; M = Zn or Cd; X = Sb or Bi) family Feng-Chuan Chuang, Marku R Perez, Rovi Angelo Villaos, Liang-Ying Feng, Aniceto B Maghirang, Chih-Peng Cheng, Zhi-Quan Huang, Chia-Hsiu Hsu, Arun Bansil Recent experiments on bulk Zintl CaAl2Si2 reveal the presence of nontrivial topological states. However, the large family of two-dimensional (2D) Zintl materials remains unexplored. Using first-principles calculations, we discuss the stability and topological electronic structures of 12 Zintl single-quintuple-layer (1-QL) AM2X2 compounds in the CaAl2Si2-structure (A = Ca, Sr, or Ba; M = Zn or Cd; and X = Sb or Bi). Phonon dispersion computations support the thermodynamic stability of all the investigated compounds. Nontrivial topological properties are determined via the calculation of Z2 invariants and edge states using the hybrid functional. Insulating topological phases driven by a band inversion at the Γ-point involving Bi-(px + py) orbitals are found in CaZn2Bi2, SrZn2Bi2, BaZn2Bi2, CaCd2Bi2, SrCd2Bi2, and BaCd2Bi2 with relatively large bandgaps. Interestingly, van Hove singularities are found in CaCd2Bi2 and BaCd2Bi2, implying the possibility of coexisting insulating and superconducting topological phases. We discuss how topological 1-QL Zintl compounds could be synthesized through atomic substitutions resulting in Janus materials (1-QL AM2XY). In particular, the thermodynamically stable Janus BaCd2SbBi film is shown to exhibit both an insulating topological state and the Rashba effect. Our study identifies a new family of materials for developing 2D topological materials platforms and paves the way for the discovery of 2D topological superconductors. |
Monday, March 6, 2023 5:24PM - 5:36PM Author not Attending |
D23.00013: Pressure-driven tunable properties of the small-gap chalcopyrite topological quantum material ZnGeSb2: A first-principles study Surasree Sadhukhan Search for new topological quantum materials is the demand to achieve substantial growth |
Monday, March 6, 2023 5:36PM - 5:48PM |
D23.00014: Experimental evidence of Weyl and Dirac relativistic spectrum at topological Volkov-Pankratov heterojunctions Joaquin Bermejo Ortiz Weyl and Dirac relativistic fermions have attracted tremendous interest in condensed matter as they mimic relativistic high-energy physics. This resemblance enables phenomena like the chiral anomaly to occur in solid state, which therefore becomes a privileged template to experimentally probe and explore fundamental relativistic theories. |
Monday, March 6, 2023 5:48PM - 6:00PM |
D23.00015: Simple Coupling Method for Topological Acoustic Metamaterial Measurement Ssu-Ying Chen Topological notions were heavily explored in condensed matter physics. |
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