Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G55: Transport and Thermodynamic Properties of Topological Systems: I |
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Sponsoring Units: DCMP Chair: Yuhang Deng, UC San Diego Room: Mile High Ballroom 2B |
Tuesday, March 3, 2020 11:15AM - 11:27AM |
G55.00001: Evidence of topological gap opening in the surface state of Bi_{2}Se_{3} by proximity to a magnetic insulator Satyaki Sasmal, Mathimalar S, Rajasekhar P, Archit Bhardwaj, Saurabh Chaudhary, Biswarup Satpati, Karthik Raman Out-of-plane magnetism at the Bi_{2}Se_{3}/EuS interface is experimentally demonstrated and theoretically proposed [1,2,3], that is expected to break time-reversal-symmetry of topologically protected surface states (SSs). However, an exchange gap (EG) opening at the Dirac point due to proximity effect of the magnetic insulator (MI), EuS, is not observed before using transport studies, primarily due to dominant bulk conduction over the SSs. By using bottom gate voltage and external magnetic field studies, we report evidence of a metal-to-insulator transition at Bi_{2}Se_{3}/EuS interface, attributed to the opening of EG, with the signature of half-integer quantum Hall effect when Fermi level is tuned into the EG [4]. Our study also shows a gate-controlled enhanced interface magnetism at Bi_{2}Se_{3}/EuS interface which we attribute to the conduction carrier-mediated RKKY interactions [3]. Our efforts in this direction with suitable MI/TI/MI device will possibly allow us to demonstrate a switchable topological electronic device using magnetic proximity effect studies. |
Tuesday, March 3, 2020 11:27AM - 11:39AM |
G55.00002: Evidence for a conducting surface state in FeSi Yuhang Deng, Yuankan Fang, Sheng Ran, Weiwei Xie, Shen Wang, Shirley Meng, Christian T Wolowiec, Ivan Schuller, Hongbo Lou, Shubin Li, Qiaoshi Zeng, John Singleton, Alexander Breindel, M Brian Maple Electrical transport measurements on high quality single crystals of FeSi show a crossover from semiconducting to metallic behavior at 19 K (T_{c}). This metallic temperature dependent resistivity points to a conducting surface ground state of FeSi, supported by the impact of surface-to-volume ratio on the resistivity of the sample, and the absence of features in specific heat at low temperature [1]. We further explore this surface state using high field magnetoresistance, high pressure, and magnetic field modulated microwave spectroscopy (MFMMS). Surprisingly, the surface sensitive MFMMS measurement of FeSi shows an anomaly near T_{c} with a signature typically associated with superconducting transitions. Based on the similarities in magnetoresistance between FeSi and the possible topological Kondo insulator SmB_{6}, FeSi could be a possible topological insulator. |
Tuesday, March 3, 2020 11:39AM - 11:51AM |
G55.00003: Magnetotransport and weak anti-localization signatures in band-engineered 3D topological insulator pn-heterostructures Thomas Mayer, Hedwig Werner, Florian Schmid, Johannes Ziegler, Elisabeth Richter, Ralf Fischer, Rebeca Diaz-Pardo, Jun Fujii, Ivana Vobornik, Dieter Karl Weiss, Christian Back, Matthias Kronseder, Dominique Bougeard To experimentally harness the novel physics arising from topological surface states (TSS) in 3D topological insulators (3D TIs) it is crucial to develop control over key band structure parameters. At the same time, controlling the contribution of bulk bands to transport has represented a major experimental challenge. |
Tuesday, March 3, 2020 11:51AM - 12:03PM |
G55.00004: Weak Antilocalization and Anisotropic Magnetoresistance in Topological Bi_{2}Te_{x}Se_{3-x} Thin Films Gregory Stephen, Owen Vail, Jiwei Lu, Patrick Taylor, Adam Friedman Topological materials, such as the quintessential topological insulators in the Bi_{2}X_{3} family (X = O, S, Se, Te), are extremely promising for beyond Moore’s Law computing applications where alternative state variables and energy efficiency are prized. It is essential to understand how the topological nature of these materials changes with growth conditions and, more specifically, chalcogen content. In this study, we investigate the evolution of the magnetoresistance of Bi_{2}Se_{3-x}Te_{x} for varying chalcogen ratios as a function of both temperature and angle of applied field. Weak antilocalization (WAL), an indicator of topological surface states, is observed to weaken with Te substitution. We also demonstrate that the anisotropy of the WAL follows the Tkachov-Hankiewicz model of magnetoconductance in topological insulators rather than a more trivial sinθ dependence. This model, which is a generalization of the Hikami-Larkin-Nagaoka model, allows for measurement of both coherence length and skin depth of the conducting surface states. These results show the surface states in Bi_{2}Se_{3} to be most isolated from the bulk states, with quality degrading through Te substitution. |
Tuesday, March 3, 2020 12:03PM - 12:15PM |
G55.00005: Quantum Oscillations in Topological Insulator β-Ag2Te with High Mobility Pengliang Leng, Xiaoyi Xie, Faxian Xiu Stimulated by the fascinating properties discovered in topological insulators, topological quantum materials have become an exciting frontier in condensed matter physics and materials science. In this study, we claim a developed growth scheme to synthesize single crystalline (β-Ag_{2}Te) nanoplates with tunable Fermi levels by chemical vapor deposition(CVD). We systemically studied the transport measurement , showing that the atomic ratio of Ag and Te can significantly change the Fermi level of Ag_{2}Te nanoplates which achieves highest reported mobility (~50000 cm^2/V*s), and significant quantum oscillations appear. By analyzing the frequency and amplitude of the quantum oscillation, we can obtain various parameters in Ag_{2}Te, and push back the energy band structure. |
Tuesday, March 3, 2020 12:15PM - 12:27PM |
G55.00006: Anomalous quantum oscillations in topological insulators Areg Ghazaryan, Emilian Nica, Onur Erten, Pouyan Ghaemi Quantum oscillations are routinely used to determine the Fermi surface (FS) in metallic systems. In topological insulators, quantum oscillations can originate from the FS of the edge states. We analyze such quantum oscillations when the chemical potential lies close to the edge of either bulk conduction or valence bands. We compare and contrast these with standard cases for edge states with 2D electron-gas and Dirac dispersions, respectively. We discuss candidate systems where deviations from the standard cases are expected to occur. We comment on the possible implications for quantum oscillations observed in topological Kondo insulators. |
Tuesday, March 3, 2020 12:27PM - 12:39PM |
G55.00007: Detection of hole pockets in type-II Weyl semimetal MoTe_{2} from Shubnikov-de Haas quantum oscillations Yajian Hu, Wing Yu, Kwing Lai, Dan Sun, Fedor Balakirev, King Yau Yip, Wei Zhang, Esteban I Paredes Aulestia, Rajveer Jha, Ryuji Higashinaka, Tatsuma D. Matsuda, Youichi Yanase, Yuji Aoki, Swee Goh The bulk electronic structure of T_{d}-MoTe_{2} features large hole Fermi pockets at the Brillouin zone center (Γ) and two electron Fermi surfaces along the Γ-X direction. However, the large hole pockets, whose existence has important implications for the Weyl physics of T_{d}-MoTe_{2}, had never been conclusively detected in quantum oscillations. In this presentation, we report an unambiguous detection of these elusive hole pockets via Shubnikov-de Haas (SdH) quantum oscillations. At ambient pressure, the quantum oscillation frequencies for these pockets are 988 T and 1513 T, when the magnetic field is applied along the c-axis. The quasiparticle effective masses m* associated with these frequencies are 1.50 m_{e} and 2.77 m_{e}, respectively, indicating the importance of Coulomb interactions in this system. We further measure the SdH oscillations under pressure. At 13 kbar, we detected a peak at 1798~T with m* = 2.86 m_{e}. Relative to the oscillation data at a lower pressure, the amplitude of this peak experienced an enhancement, which can be attributed to the reduced curvature of the hole pockets under pressure. Combining with DFT + U calculations, our data shed light on why these important hole pockets had not been detected until now. |
Tuesday, March 3, 2020 12:39PM - 12:51PM |
G55.00008: Magnetothermoelectricity of topological semiconductor ZrTe_{5 } Junbo Zhu, Changmin Lee, Takehito Suzuki, Shiang Fang, Nuh Gedik, Joseph G Checkelsky We report a comprehensive study of electric, thermoelectric, thermodynamic measurements and angle resolved photoemission spectroscopy (ARPES) of the topological insulator candidate ZrTe_{5}. The single crystals grown by a chemical vapor transport method exhibit transport properties characterized by the electronic band structure with a small band gap that is observed by ARPES. The thermoelectricity has a significant response to magnetic field exceeding 300%, for which we discuss the mechanism along with the unique properties of bands deduced from the fermiology. |
Tuesday, March 3, 2020 12:51PM - 1:03PM |
G55.00009: Resonant and Magnetic Doping in Topological Insulator Bi_{2}Se_{3} Brandi Wooten, Patrick Taylor, Joseph P C Heremans Topological insulators (TI) are bulk insulators with topologically protected, electrically conducting surface states. Unfortunately, “practical” topological protection is observed rarely. Interactions between bulk and surface electrons result in surface electrons having short lifetimes and experiencing strong dephasing that impedes possible applications, e.g., in quantum computing.^{1} We exploit resonant doping to reduce the bulk carrier concentration to meet the Mott criterion for the metal-insulator transition: the number of electrons due to unintentional doping, n_{D}, must be less than the critical carrier concentration, n_{c}; . Se vacancies make Bi_{2}Se_{3} heavily n-type, and the Mott criterion is not reached. By adding resonant dopant Sn to Bi_{2}Se_{3}, the density of states is widened at the top of the valence band, decreasing n_{c} by an order of magnitude, allowing for the Mott criterion to be satisfied.^{2} Seebeck measurements show a sign change for Sn-doped Bi_{2}Se_{3} as temperature is reduced, hinting that this approach works. Further, we plan to add magnetic dopant, Mn, and perform in-field transport measurements. |
Tuesday, March 3, 2020 1:03PM - 1:15PM |
G55.00010: Identification of massive and topological surface states in the 3D topological insulator tensile strained HgTe Valentin L. Müller, David Mahler, Lukas Lunczer, Jonas Wiedenmann, Wouter Beugeling, Hartmut Buhmann, Laurens W Molenkamp Topological surface states (TSS) with their linear dispersion and spin momentum locking constitute an interesting playground for basic research and future applications and have been identified in the topological insulator tensilely strained HgTe by magnetotransport measurements [1]. While the TSS are created due to the inversion of the bulk bands, additional surface states of different origin have been reported in gated devices of the topological insulator and the Dirac semi-metal phase of HgTe [2, 3]. These additional surface states are formed due to the shape of the electrochemical potential introduced by the electric field of the gate and are of general interest, since they can also be present in other topological materials. They are called massive Volkov-Pankratov states (VPS) after their first report in Ref. [4]. |
Tuesday, March 3, 2020 1:15PM - 1:27PM |
G55.00011: Transport evidence of Dirac dispersion in PbBi_{2}Te_{4} 3D topological insulator PRIYANATH MAL, GANESH BERA, BIPUL DAS, Archana Lakhani, G. R. Turpu, C. V. Tomy, PRADIP DAS The non-trivial nature of the surface states in PbBi_{2-x}Fe_{x}Te_{4} is evident from the observations of the Shubnikov-de Haas (SdH) oscillations with π berry phase. Lower effective mass obtained from the Lifshitz-Kosevich fit and higher mobility values determined from the Dingle analysis confirmed the surface origin of the oscillations. An elongated band outside the surface Fermi surface is identified for pure sample and is absent for doped specimens. Combined SdH oscillations and Hall effect studies reveal the shifting of the Fermi level of PbBi_{2}Te_{4} towards the Dirac point with successive Fe doping. Progressive decrease of the Fermi wave vector (k) and corresponding Fermi energy (E) with Fe doping can be fitted well with straight line, reveals the linear nature of the E-k diagram i.e. Dirac dispersion of topological surface states in PbBi_{2}Te_{4}. The observed weak anti-localization corroborates the spin-momentum locking as the consequence of π Berry phase acquires by the spin upon moving round the Dirac point and is consistent with SdH oscillations. |
Tuesday, March 3, 2020 1:27PM - 1:39PM |
G55.00012: Theory of drude-like nonlinear thermoelectric responses in quantum many-body systems Xu Yang, Ying Ran A well-defined Drude peak in the linear electrical response is a fundamental feature of good metals, which has served as a basic probe of quantum materials irrespective of whether correlation is strong or not. We theoretically investigate Drude-like physics in general second-order nonlinear thermoelectric responses in time-reversal invariant noncentrosymmetric quantum many-body systems. The physical interpretations of the corresponding Drude weights are clarified, and the Drude relaxation time is discussed in the framework of the memory matrix technique. In particular, in linear responses the Drude weight is known to be related to the adiabatic derivative of the current with respect to twisted boundary conditions; while in the nonlinear case we find that the Drude weights are related to the adiabatic derivatives of dissipationless linear responses. In addition, we prove a general nonlinear reciprocal relation, and discuss nonlinear generalizations of the Lorentz ratio. Our results generalize the nonlinear Hall effect pointed out by Sodemann and Fu, and hold irrespective of whether quasiparticle descriptions are valid at low energies or not, indicating that nonlinear thermoelectric responses can serve as additional probes of strongly correlated systems such as non-Fermi liquids. |
Tuesday, March 3, 2020 1:39PM - 1:51PM |
G55.00013: Universal transport signatures of the topological phase transition in Majorana wires Aaron Chew, Wenyu He, Jason F. Alicea Detecting the predicted magnetic-field-driven topological phase transition in proximitized nanowires is a key problem in the ongoing quest for unambiguous signatures of Majorana zero modes. We investigate the transport properties of a junction between a Luttinger liquid lead and a proximitized nanowire held at the topological phase transition. Upon fine-tuning a single parameter at the interface, the junction can realize a novel nontrivial fixed point at which electrons in the lead split into two propagating Majorana fermions, one that perfectly transmits into the critical nanowire and one that reflects. We introduce a bosonized framework for this fixed point and extract universal conductance signatures of the topological phase transition. We also comment on applications to tunneling into the edge of a two-dimensional topological superconductor. |
Tuesday, March 3, 2020 1:51PM - 2:03PM |
G55.00014: Anomalous magnetotransport at a two-dimensional correlated electron system Edouard Lesne, Yildiz Saglam, Thierry van Thiel, Pierre Bruneel, Ana Monteiro, Gary Steele, Marc Gabay, Andrea Caviglia The emergent two-dimensional electron system (2DES) formed at the interface between LaAlO_{3} (LAO) and SrTiO_{3} (STO) insulating oxides has been a subject of great interest in condensed matter physics over the last decade. Recently, the (111)-oriented STO based 2DES has attracted further attention due to its sixfold orbital and lattice symmetry whereby two consecutive planes form a dense honeycomb lattice of Ti 3d orbitals, a host candidate for prospective topologically non-trivial electronic phases. Furthermore, we have demonstrated that the (111)-LAO/STO interface exhibits an electronic correlation driven reconstruction of its band structure, and a two-dimensional superconducting groundstate, both tunable by electrostatic field-effect. |
Tuesday, March 3, 2020 2:03PM - 2:15PM |
G55.00015: Resistively detected nuclear magnetic resonance in topological insulators Zekun Zhuang, Vesna F Mitrovic, John Bradley Marston Topological insulators (TI) possess helical edge or surface states that are protected by both time-reversal symmetry and topology. We will present our proposal to use resistively detected nuclear magnetic resonance (RDNMR) to characterize Dirac fermions at the edge or surface of the TI. The effects of nuclear spins on the edge state conductance in both 2-D and 3-D TIs will be presented. |
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