Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session J45: Electronic Structure and Magnetism in Topological MaterialsLive
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Sponsoring Units: DCMP Chair: Sabin Regmi, University of Central Florida |
Tuesday, March 16, 2021 3:00PM - 3:12PM Live |
J45.00001: Inducing anisotropies in Dirac fermions by periodic driving Alvaro Diaz Fernandez Floquet engineering of topological phases is becoming increasingly popular. One particular example of great interest is that of Floquet topological insulators [1]. In our work, we consider the three-dimensional Hamiltonian for Bi2Se3, a second-generation topological insulator, under the effect of a periodic drive for both in-plane and out-of-plane fields. As it will be shown by means of high-frequency expansions up to second order in the Floquet Hamiltonian, the driving induces anisotropies in the Dirac cone and opens up a quasienergy gap for in-plane elliptically polarized fields. Analytic expressions are obtained for the renormalized velocities and the quasienergy gap [2]. These expressions are then compared to numerical calculations performed by discretizing the Hamiltonian in a one-dimensional lattice and following a staggered fermion approach [3], achieving a remarkable agreement. We believe our work may have an impact on the transport properties of topological insulators. |
Tuesday, March 16, 2021 3:12PM - 3:24PM Live |
J45.00002: Unusual change in the electronic structure of a semimetal NdSb across the magnetic transition* Anup Pradhan Sakhya, M. Mofazzel Hosen, Sabin Regmi, Baokai Wang, Gyanendra Dhakal, Klauss Dimitri, Firoza Kabir, Christopher Sims, Luis Persaud, Eric D Bauer, Filip Ronning, Arun Bansil, Madhab Neupane The rare-earth monopnictide (REM) materials host complex magnetic ground states and have recently attracted considerable research interest as it serves as a promising platform to investigate the interplay between strong electron correlation and topological phases. Here, we have reported a systematic investigation of the Fermi surface and the band dispersion of a correlated semimetal NdSb in the paramagnetic (PM) phase as well as the antiferromagnetic (AFM) phase (TN ~ 15 K) using angle-resolved photoemission spectroscopy (ARPES). Our data reveals a clear distinct band evolution phenomenon due to the antiferromagnetic phase transition. Most importantly, a complex band structure is observed at the zone center which is potentially due to the strong hybridization induced by the magnetic phase transition. Our experimental study opens up a new path to understand the intricate interplay between magnetism, and electron correlation in this REM family. |
Tuesday, March 16, 2021 3:24PM - 3:36PM Live |
J45.00003: Classification of radial spin textures in chiral crystals Daniel Gosalbez Martinez, Stepan Tsirkin, Oleg Yazyev Radial spin textures in momentum space have been shown to appear around the Kramers-Weyl points of chiral crystals. Such spin textures are not unique to those band degeneracies, but they appear, regardless of the number of bands, at any high-symmetry point where at least two rotation or screw symmetry axes intersect. The two highest valence bands around the H point of trigonal Tellurium are an example of such radial spin texture in single degenerate bands [1]. In this work, we classify the different spin textures allowed by symmetry at the high-symmetry points of the chiral point groups. We found that basic spin textures in momentum space such as Hedgehog, Néel-type skyrmion and antiskyrmion can be found, but also much complex spin structures with cubic momentum dependence. We reveal all these spin textures in the band structure of Tellurium [2]. |
Tuesday, March 16, 2021 3:36PM - 3:48PM Live |
J45.00004: A Fermi Arc Ladder Reveals Higher-Fold Topology Tyler Cochran, Guoqing Chang, Ilya Belopolski, Daniel S Sanchez, Kaustuv Manna, Zijia Cheng, Xian Yang, Daniel Multer, Jiaxin Yin, Songtian Zhang, Nana Shumiya, Jaime A Sanchez, Patrick Le Fèvre, François bertran, Vladimir N. Strocov, Takayuki Muro, Jonathan Denlinger, Claudia Felser, Hsin Lin, Zahid Hasan While topological insulators and Weyl semimetals have been major topics within materials research, theoretical and experimental focus has begun to shift to more exotic forms of topological quantum matter. Higher-fold topology is one example, where the low-energy description goes beyond Standard Model analogs. Despite intensive experimental studies, conclusive evidence remains elusive for the topological nature of higher-fold chiral fermions. In this work, we leverage a photoemission spectroscopy probe to discover the multi-gap topology of a higher-fold chiral fermion material [1]. We identify two sets of chiral surface states. These Fermi arcs exhibit an emergent ladder structure in energy-momentum space, unprecedented in topological materials. Furthermore, we determine the multi-gap chiral charge C=(2,2). Our results provide a general framework to explore future complex topological materials. |
Tuesday, March 16, 2021 3:48PM - 4:00PM Live |
J45.00005: Electronic Structure and Properties of 2M WS2 William Scougale, Rabindra Dulal, Piumi Samarawickrama, Joseph McBride, Brian Leonard, John Ackerman, Jifa Tian, Sung-Kwan Mo, Eli Rotenberg, Te-Yu Chien The recently observed Majorana Zero Mode (MZM) in 2M Phase of Tungsten Disulfide (2M WS2) opens a new opportunity in the applications in quantum computing. The topologically protected quantum state can overcome issues such as decoherence and noise induced by local fluctuations to reduce the errors produced during computation by braiding the MZMs in topological superconductors. 2M WS2 is a recently confirmed intrinsic topological superconductor with a high superconducting transition temperature of 8.8 K, which provides an excellent playground to explore the novel properties of the MZMs. In this work, we explore the electronic structure of 2M WS2 using STM and angle resolved photoemission spectroscopy (ARPES). We observed defect/impurity induced doping, resulting in a ~10 meV shift in the dI/dV spectrum. We also observed a twisting distortion of ~8 degrees off the crystallographic axis in STM atomic resolution images. This twisting distortion has also been reported in other transition metal dichalcogenides (TMD)s, indicating this distortion might be a universal phenomenon in TMD materials. Finally, the preliminary ARPES data exhibits dispersive bands, qualitatively agreeing with the DFT calculated band structures. |
Tuesday, March 16, 2021 4:00PM - 4:12PM Live |
J45.00006: Giant Photonic Response of Mexican-hat Topological Semiconductors for Mid-infrared to THz Applications Haowei Xu, Jian Zhou, Hua Wang, Ju Li The mid-infrared (MIR), far-infrared (FIR) to terahertz (THz) frequencies are the least developed parts of the electromagnetic spectrum for applications. Traditional semiconductor technologies like laser diodes and photodetectors are successful in the visible light range, but are still confronted with great challenges when extended into the MIR/FIR/THz range. We demonstrate that topological insulators (TIs), especially those with Mexican-hat band structure (MHBS), provide a route to overcome these challenges. The optical responses of MHBS TIs can be one to two orders of magnitude larger than that of normal semiconductors at the optical-transition edge. We explore the databases of topological materials and discover a number of MHBS TIs whose bandgaps lie between 0.05~0.5 eV and possess giant gains (absorption coefficients) on the order of 104~105 cm-1 at the transition edge. These findings may significantly boost potential MIR/FIR/THz applications such as photon sources, detectors, ultrafast electro-optical devices, and quantum information technologies. |
Tuesday, March 16, 2021 4:12PM - 4:24PM Live |
J45.00007: Electron transport in the topological metal Molybdenum Phosphide Sushant Kumar, Ravishankar Sundararaman With aggressive down-scaling of integrated circuits and the concomitant reduction of the dimensions of the interconnect lines, the search for a new interconnect material to replace the ubiquitously used Cu has become more important than ever. When the electron mean free path, λ becomes equal to or less than the dimensions of the interconnect lines, there is a dramatic increase in the resistivity, ρ which adversely impacts the efficiency and performance of the circuits. Hence, there is an ongoing search for metals that could supplant copper as the narrow interconnect metal. While conventional metals like cobalt, ruthenium and iridium are being considered as substitutes, there has been an increased interest in other non-elemental metals (like intermetallics and MAX phases) and topological metals (like MoP). In this work, we use first-principles calculations to evaluate the performance and prospect of a topological semi-metal MoP as a future interconnect material. We perform Landauer conductance calculations for different orientations and film thicknesses. The change in conductance with the introduction of surface vacancies and defects throw light on the topological protection offered to electron transport by MoP. |
Tuesday, March 16, 2021 4:24PM - 4:36PM Live |
J45.00008: Symmetry-Enforced Dirac and Nodal-Line States in Nonsymmorphic α-Bismuthene/Antimonene Qiangsheng Lu, Kyle Yu Chen, Matthew Snyder, Jacob Cook, Tung Nguyen, Guang Bian Nonsymmorphic crystal symmetries can enforce the formation of Dirac and nodal line states, providing a new route to establishing symmetry-protected states in 2D materials. Here we will discuss our recent work on the realization of the symmetry-enforced Dirac and nodal-line states in nonsymmorphic α-bismuthene/Antimonene (Bi/Sb monolayer). The bismuthene/antimonene was synthesized by the method of molecular beam epitaxy. The symmetry-protected band structure was observed by angle-resolved photoemission experiments. The Dirac and nodal-line states are located at high-symmetry momentum points and lines in the 2D Brillouin zone. The locations are entirely determined by the lattice symmetry. In addition, the Dirac fermions in α-bismuthene is of spin-orbit type in contrast to the spinless Dirac states in graphene. The result will accelerate the search of 2D materials with symmetry-protected states and extend “graphene” physics into new territory where strong spin-orbit coupling is present. |
Tuesday, March 16, 2021 4:36PM - 4:48PM Live |
J45.00009: Unlocking nonlinear optical phenomena due to spin-orbit and Zeeman interactions in the graphene family topological insulators Rajesh Malla, Avadh Saxena, Wilton J De Melo Kort-Kamp Two-dimensional buckled monolayers of the graphene family, namely silicene, germanene, stanene, and plumbene, possess non-negligible intrinsic spin-orbit coupling which opens a gap in the Dirac-like energy band structure. Each gap can be tailored with external fields to drive the system via different topologically insulating phases. Due to the in-plane spatial symmetry of the low energy Hamiltonian of these materials, investigations of their nonlinear optical response within the electric dipole approximation have been limited to odd-order harmonics. In this work, we show that although a Rashba spin-orbit coupling and an in-plane Zeeman interaction cannot independently break this in-plane spatial symmetry, together they are able to do so, which leads to a nonlinear optical response that includes the generation of even harmonics. We further explore the effect of second harmonic generation near various topological phase transitions. |
Tuesday, March 16, 2021 4:48PM - 5:00PM Live |
J45.00010: Topological Phase Transition Induced by Partial Ordering of Heavy Alkali Adatoms in Graphene Monolayer Daniel Nagy, Balazs Dora, Janos Koltai, Laszlo Oroszlany Topological insulators host robust, spin-polarized edge states, hence they are |
Tuesday, March 16, 2021 5:00PM - 5:12PM Live |
J45.00011: Tuning the Surface Spin Textures of Topological Materials Yuefeng Yin, Michael S Fuhrer, Nikhil V. Medhekar Spin manipulation is a big challenge for spintronic devices. Many interesting physical phenomena come from playing with spin polarizations with electric field, magnetic field and photons. Effective control over spin current is critical for using spintronics in information processing. Here we explore the surface spin textures of topological materials using first principles calculations and Wannier tight-binding models. We have observed a transition from in-plane to out-of-plane spin polarizations on the surface of a topologically nontrivial pyrite-type crystal OsX2 (X=Se, Te). The energy screening of bulk bands leads to selective filtering of the magnitude and orientations of the surface spin polarizations. We have further investigated fine tuning of surface spin textures by external factors. We expect these results could provide new insights of correlations between band topology and spin polarizations and assist the design of future spintronic devices. |
Tuesday, March 16, 2021 5:12PM - 5:24PM Live |
J45.00012: Tuning the Edge States of Bismuthene via Substrate Effects Chutian Wang, Yuefeng Yin, Michael S Fuhrer, Nikhil V. Medhekar One of the challenges in the field of topological material studies is how to maintain the nontrivial topological behaviour in a practical condition. In this work, we study the robustness of edge states in a two-dimensional topological crystalline insulator (2D TCI) and approaches of modifying them based on a planar bismuthene model. Using first principles calculations and Wannier tight-binding models, we have found that the mirror symmetry protected non-trivial topological phase can be maintained when the thin film has weak interaction with the substrate, or when a sandwich stacking is applied. We have also shown that spin-filtered edge current of 2D TCI can survive strong mirror symmetry breaking field when they have certain edge terminations. Finally we have demonstrated by modulating the interfacial distance, or applying rotation on sandwich structures, bismuthene edge band gap can be opened, which effectively switches off the nontrivial topological states. This research can provide guidelines for methodology to tune or maintain those edge states in the design of TCI-based electronic devices. |
Tuesday, March 16, 2021 5:24PM - 5:36PM Live |
J45.00013: Tight-binding models for two-dimensional allotropes of bismuth-based on localized Wannier functions Qile Li, Jackson Smith, Yuefeng Yin, Chutian Wang, Mykhailo V Klymenco, Jared H Cole, Nikhil V. Medhekar Bismuth and bismuth-based compounds have played critical roles in the development of topological band theories and topological electronic devices. We have constructed tight-binding models based on the Wannier basis derived from first principles calculations to investigate the electronic structure of two-dimensional bismuth allotropes. We have successfully captured the electronic and topological features of the three types of two-dimensional bismuth allotropes (Bi(111) bilayer, Bi (110) bilayer and planar bismuthene) with minimum number of tight-binding parameters. We have demonstrated the importance of the connections between crystalline symmetries and band topology. Moreover, we have extended our approach to other similar two-dimensional topological materials. We expect these simple but accurate tight-binding models can help to effectively investigate the transport behavior in two-dimensional electronic devices. |
Tuesday, March 16, 2021 5:36PM - 5:48PM On Demand |
J45.00014: Observation of sixfold degenerate fermions in a superconducting metal. Xian Yang, Tyler Cochran, Ramakanta Chapai, Damien Tristant, Jiaxin Yin, Ilya Belopolski, Zijia Cheng, Daniel Multer, Ilya Vekhter, William A Shelton, Rongying Jin, Suyang Xu, Zahid Hasan Condensed matter systems offer a unique platform to study fermions from high energy physics. It is well-known that Dirac and Weyl fermions with four- and twofold degeneracy were visualized in topological quantum materials recently. Beyond these fundamental fermions in high energy physics, it has been proposed that crystal and time-reversal symmetries in solids can also protect three-, six- and eightfold degenerate band crossings. These exotic fermions have no high energy analogues due to Poincare invariance. In this talk, I will present our ultrahigh resolution photoemission study on a superconducting metal that hosts three doubly degenerate quadratic bands at the R point, demonstrating a topological fermion beyond the constraints of high energy physics. |
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