Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S70: Tuning and Manipulation of Topological Materials IFocus Recordings Available
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Chair: Qingfeng Wang, University of Maryland, College Park Room: Hyatt Regency Hotel -Jackson Park B |
Thursday, March 17, 2022 8:00AM - 8:12AM |
S70.00001: Gate-Defined Tellurium Nanowire Quantum Dots Shiva Davari Dolatabadi, Kenji Watanabe, Takashi Taniguchi, Hugh O Churchill Chiral crystals of elemental Te are Weyl semiconductors with the intriguing property of combining Weyl physics with a small semiconducting band gap, which enables the creation of gate-tunable devices to probe and utilize the topological properties of Te. Specifically, the formation of gate-defined quantum dots in Te would allow Coulomb blockade spectroscopy to provide information about the strength of exchange interaction, spin-orbit coupling, and g-factors associated with discrete quantum states in Te nanostructures. This talk presents our progress in this direction using low-pressure PVD-grown Te nanowires with local control of carrier density using electrostatic gates. While atomically flat hexagonal boron nitride (hBN) gate dielectrics have been widely used for high quality layered material devices, the relatively weak adhesion to Te nanowires makes hBN-insulated Te device assembly challenging. We compare different strategies involving more traditional dielectrics, as well as a hybrid approach that uses a global Si backgate and hBN-insulated local top gates for Weyl semiconductor devices. |
Thursday, March 17, 2022 8:12AM - 8:24AM |
S70.00002: Characterization of In1-xMnxAs/GaSb Quantum Wells by Shubnikov de Haas Oscillations and Cyclotron Resonance Logan S Riney, Seul-Ki Bac, Xinyu Liu, Joaquin B Ortiz, Roland Winkler, Jiashu Wang, Louis-Anne DeVaulchier, Yves Guldner, Tatyana Orlova, Maksym Zhukovskyi, Jacek K Furdyna, Malgorzata Dobrowolska, Badih A Assaf The InAs/GaSb broken gap III-V heterojunctions can host a two-dimensional quantum spin Hall state resulting from a band-inverted electronic structure. At the interface between the two materials, the InAs conduction band edge lies below the GaSb valence band edge. The hybridization of these levels cause a topological gap to open. The observation of the quantum anomalous Hall effect (QAHE) is expected to occur if the s-p ordering is inverted (non-trivial) for one spin species and trivial for the other, which can be achieved through the introduction of Mn into system. In this work, we characterize a series of Mn doped InAs/GaSb type-II quantum wells. Robust SdH oscillations and Hall quantization between 1.5K and 50K are observed in magneto-transport. We perform magneto-optics up to 15T to measure the cyclotron mass. We find that at high Mn content, InMnAs/GaSb samples are p-type, while at intermediate content, they host a coexisting 2DEG and hole channel that can either be due to band bending or a Mn impurity level. We hypothesize that Mn can serve both as a source of magnetic exchange and Fermi level pinning in InAs/GaSb. |
Thursday, March 17, 2022 8:24AM - 8:36AM |
S70.00003: Enantiomerically Specific Nonlinear Optical Responses in Chiral Weyl Semimetals Manita Rai, Sujan B Subedi, Chandra Shekhar, Kaustuv Manna, Claudia Felser, Darius H Torchinsky Weyl semimetals that break all structural mirror symmetries may comprise Weyl nodes of opposite Chern number that are offset in energy, making these systems ideal for studying the optical properties of an individual Weyl node without interference from its opposite sign partner. Since these materials are acentric, they can also host helicity dependent, second order nonlinear optical responses from both bulk [1, 2] and surface states [3]. In this talk, we will describe the effect of structural handedness on shift current, injection current and second harmonic generation in the structurally chiral Weyl semimetal PdGa over the 0.475 – 1.5 eV photon energy range and discuss the effect of topological order on the material response. |
Thursday, March 17, 2022 8:36AM - 9:12AM |
S70.00004: Weyl-node-driven domain wall motion and collective magnetism in double-symmetry-breaking Weyl semimetals Invited Speaker: Hung-Yu Yang In the RAlX (R = rare-earths, X = Ge/Si) material family where both inversion and time-reversal symmetry are broken, not only the magnetic Weyl nodes are stabilized, but also interesting interactions are enabled and can lead to new Weyl physics [1-8]. The abundance of robust magnetic Weyl semimetals in the RAlX family allows for domain wall motion and collective magnetism related to Weyl nodes to emerge. We give an overview of rich domain wall physics in different RAlX materials revealed by scanning SQUID microscopy [3, 4], magneto-optical Kerr effect [5], and small-angle neutron scattering [6], and Weyl-mediated magnetism detected by neutron diffraction [6, 7]. In particular, we highlight the unusual electrical transport driven by domain walls and Weyl nodes [6, 8], and collective magnetism driven by Weyl-mediated interactions [7]. We demonstrate that the double-symmetry-breaking RAlX family is a promising avenue for new Weyl physics. |
Thursday, March 17, 2022 9:12AM - 9:24AM |
S70.00005: Extreme Electron-Phonon Coupling in Topological Semimetal NbGe2. Vincent M Plisson Weyl semimetals are topological systems that have generated considerable interest due to their transport properties. One of the mechanisms that may play an important role in the manifestation of these transport properties is electron-phonon coupling. Previous optical experiments done on various Weyl semimetals have already shown phonon linewidths deviating from the usual model of anharmonic decay. Here we report on Raman measurements performed on a new topological semimetal. Careful analysis reveals the lifetime is consistent with electron-phonon coupling far in excess of the anharmonic decay channels. |
Thursday, March 17, 2022 9:24AM - 9:36AM |
S70.00006: Quantum Geometry of Light-Matter Interactions: New Approach to Multi-Band Physics Junyeong Ahn, Guang-Yu Guo, Naoto Nagaosa, Ashvin Vishwanath Geometry of quantum states has proved to be a useful concept for understanding responses of electronic systems to static electromagnetic fields. However, it has been challenging to relate quantum geometry with resonant optical responses. The main obstacle is that optical transitions are properties of a pair of states, while existing geometrical properties are defined for a single state. Therefore, concrete geometric understanding of optical responses has been limited to two-level systems, where one of two states determines the Hilbert space completely. Here, we construct a general theory of Riemannian geometry for resonant optical processes, by identifying transition dipole moment matrix elements as tangent vectors. This theory applies to arbitrarily high-order responses, suggesting that optical responses can be generally thought of as manifestations of the Riemannian geometry of quantum states. We use our theory to show that third-order photovoltaic Hall effects are related to the Riemann curvature tensor and demonstrate an experimentally accessible regime where they dominate the response. We discuss the implications of this theory to multiband physics in quantum materials. |
Thursday, March 17, 2022 9:36AM - 9:48AM |
S70.00007: Towards a topological phase diagram for SmB6 alloys Lewis A Wray, Yishuai Xu, Erica Kotta, Jae Woong Lee, Beongki Cho, Shouzheng Liu, Turgut Yilmaz, Elio Vescovo, Jonathan D Denlinger, Lin Miao SmB6 is a strongly correlated material that has been attributed as a topological insulator and a Kondo insulator. The bulk insulating character of SmB6 is surprisingly robust against nominal carrier doping, however the robustness of the band topology picture within alloys is less clear. I will present angle resolved photoemission measurements that characterize the loss of topological band structure features as a function of carrier doping and decoherence in Eu- and Ce- alloyed samples. Topologically associated features are observed out to unprecedented 30% Eu and 50% Ce concentrations. These properties are interpreted in the context of a recent re-designation of the conduction band, and provide the bases to propose a new low energy heirarchy of electronic symmetries involved in the insulating gap and topological surface states. |
Thursday, March 17, 2022 9:48AM - 10:00AM |
S70.00008: Chemical tuning effects on the extreme magnetoresistance of Dirac node arcs semimetal PtSn4 Samikshya Sahu, Mohamed Oudah, Alannah M Hallas PtSn4 is a novel topological semimetal and hosts Dirac arcs in its momentum space such that the conduction and valence band touch in loops and not at a point or line. One of the dominating electronic properties for this material is its ultrahigh magnetoresistance (XMR) at low temperature, which onsets at 30K. This XMR has been linked to the unique energy dispersion and gapless band crossings, which impart topological character to the PtSn4 structure. Hence, the XMR can be seen as inextricably linked to the topology, as in WTe2, NbP, and others. In this talk, I will address the chemical and electronic properties related to the topology of the band structure of PtSn4 and explain what happens to these properties when we try and perturb the system via chemical substitutions. We replace some of the Pt in the PtSn4 with Au/Ir and characterize the structural modifications and the effects on the XMR. Understanding this interplay between the electronic, chemical, and topological properties can provide us with the much-needed playground to find and investigate these Dirac node arcs based topological semimetals. |
Thursday, March 17, 2022 10:00AM - 10:12AM |
S70.00009: Discovery of a three-dimensional topological Dirac semimetal, KZnBi and its surface superconducting state. Junseong Song, Sunghun Kim, Youngkuk Kim, Young Hee Lee, Binghai Yan, Yeongkwan Kim, Sung Wng Kim Topological matters with superconducting state provide an exotic platform for realizing Majorana fermions that promise the building block of a quantum computation. Here we report the discovery of a new three-dimensional (3D) topological Dirac semimetal (TDS) material KZnBi, coexisting with a naturally formed superconducting state on the surface under ambient pressure. Using photoemission spectroscopy together with first-principles calculations, a 3D Dirac state with linear band dispersion is identified. The characteristic features of massless Dirac fermions are also confirmed by magnetotransport measurements, exhibiting an extremely small cyclotron mass of m* = 0.012 m0 and a high Fermi velocity of vF = 1.04 × 106 m/s. Interestingly, superconductivity occurs below 0.85 K on the (001) surface, while the bulk remains nonsuperconducting. The captured linear temperature dependence of the upper critical field suggests the possible non-s-wave character of this surface superconductivity. Our discovery serves a distinctive platform to study the interplay between 3D TDS and the superconductivity. |
Thursday, March 17, 2022 10:12AM - 10:24AM |
S70.00010: Confined vs. extended Dirac surface states in topological crystalline insulator nanowires Roni Majlin Skiff, Fernando de Juan, Raquel Queiroz, Haim Beidenkopf, Roni Ilan Confining two-dimensional Dirac fermions on the surface of topological insulators has remained an outstanding conceptual challenge. In this work, we show that Dirac fermion confinement is achievable in topological crystalline insulators (TCI), which host multiple surface Dirac cones depending on the surface termination and the symmetries it preserves. This confinement is most dramatically reflected in the flux dependence of these Dirac states in the nanowire geometry, where different facets connect to form a closed surface. Using SnTe as a case study, we show how wires with all four facets of the <100> type display pronounced and unique Aharonov-Bohm oscillations, while nanowires with the four facets of the <110> type such oscillations are absent due to strong confinement of the Dirac states to each facet separately. Our results place TCI nanowires as a versatile platform for confining and manipulating Dirac surface states. |
Thursday, March 17, 2022 10:24AM - 10:36AM |
S70.00011: Field Tunable Normal and Hybrid Spin Texture of Halide Perovskites Mayank Gupta, B. R. K. Nanda Hybrid organic-inorganic halide perovskites (HOIP) are discovered to be the promising class of materials for optoelectronics, and spinorbitronics due to the presence of strong spin-orbit coupling and spontaneous ferroelectric polarization. Here, we develop a model Hamiltonian to describe the electronic structure and spin texture of HOIP. The Hamiltonian takes into account the electron hopping, spin-orbit coupling, and the effect of the polarized field. From the results, we infer that the spin texture is far more sensitive to the polarized field and can be served as a fingerprint for the HOIPs.The formation of cusp and nodes in the spin texture spanned across the Brillouin zones well as possible hybridization in the spin texture, driven through band inversion, can give rise to a unique spin transport phenomena in these perovskites. Furthermore, we will see the polarized field can lead to first order normal to topological phase transition and can create unconventional topological phases in the form of Dirac circles and arches. We support our findings with density functional calculations. |
Thursday, March 17, 2022 10:36AM - 10:48AM |
S70.00012: Lorentz-boost-driven magneto-optics in Dirac matter Xin Lu, Jan Wyzula, Milan Orlita, Dibya K Murkehjee, Ivan Mohelský, Florian Le Mardelé, Raman Sankar, Benjamin A Piot, David Santos-Cottin, Wei-Li Lee, Marek Potemski, Yuriy Krupko, Mark O Goerbig, Jiri Novák, Mario Novak, Ana Akrap, Xin Lu Optical and magneto-optical methods can determine experimentally the energy band gap with a great precision. Here we show that such conventional methods, applied with great success to many materials in the past, do not work in topological Dirac semimetals with a dispersive nodal line. There, the optically deduced band gap depends on how the magnetic field is oriented with respect to the crystal axes. Such highly unusual behaviour is explained in terms of band-gap renormalization driven by Lorentz boosts, accompanied by an interpretation in the language of condensed matter physics. |
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