Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session H28: Topological Crystalline Insulators and Quantum Hall Effects.Focus
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Sponsoring Units: DMP Chair: Vidya Madhavan, University of Illinois, Urbana-Champaign Room: 327 |
Tuesday, March 15, 2016 2:30PM - 3:06PM |
H28.00001: Identification of odd-parity nematic superconductivity in doped topological insulators Invited Speaker: Liang Fu I will review our theoretical proposal [1] that CuxBi2Se3, a doped topological insulator that becomes superconducting below Tc = 3.8K, may have an odd-parity superconducting order parameter emerging from a strongly spin-orbit-coupled band structure. I will discuss recent experimental discovery of spontaneously rotational symmetry breaking in the superconducting state of CuxBi2Se3 [2], which provides strong evidence for a two-component odd-parity order parameter leading to nematic superconductivity [3]. Our theoretical analysis shows that this nemetic superconductor is stabilized by spin-orbit coupling [4], exhibits a variety of novel thermodynamic properties [5], and realizes a time-reversal-invariant topological superconductor. [1] L. Fu and E. Berg, PRL 105, 097001 (2010) [2] K. Matano, M. Kriener, K. Segawa, Y. Ando and G. Zheng, arXiv:1512.07086 [3] L. Fu, PRB, 90, 100509 (2014) [4] J. Venderbos, V. Kozii, and L. Fu, arXiv:1512.04554 [5] J. Venderbos, V. Kozii, and L. Fu, to appear [Preview Abstract] |
Tuesday, March 15, 2016 3:06PM - 3:18PM |
H28.00002: Two-dimensional Topological Crystalline Insulator Phase in Sb/Bi Planar Honeycomb with Tunable Dirac Gap Chia-Hsiu Hsu, Zhi-Quan Huang, Christian Crisostomo, Liang-Zi Yao, Feng-Chuan Chuang, Yu-Tzu Liu, Baokai Wang, Chuang-Han Hsu, Chi-Cheng Lee, Hsin Lin, Arun Bansil We predict planar Sb/Bi honeycomb to harbor a two-dimensional (2D) topological crystalline insulator (TCI) phase based on first-principles computations. Although buckled Sb and Bi honeycombs support 2D topological insulator (TI) phases, their structure becomes planar under tensile strain. The planar Sb/Bi honeycomb structure restores the mirror symmetry, and is shown to exhibit non-zero mirror Chern numbers, indicating that the system can host topologically protected edge states. Our computations show that the electronic spectrum of a planar Sb/Bi nanoribbon with armchair or zigzag edges contains two Dirac cones within the band gap and an even number of edge bands crossing the Fermi level. Lattice constant of the planar Sb honeycomb is found to nearly match that of hexagonal-BN. The Sb nanoribbon on hexagonal-BN exhibits gapped edge states, which we show to be tunable by an out-of-the-plane electric field, providing controllable gating of edge state important for device applications. [Preview Abstract] |
Tuesday, March 15, 2016 3:18PM - 3:30PM |
H28.00003: Topological crystalline insulators and superconductors with order-two nonsymmorphic symmetry Ken Shiozaki, Masatoshi Sato, Kiyonori Gomi Topological crystalline insulators (TCIs) and topological crystalline superconductors (TCSCs) are symmetry protected topological phases of free fermions with space group symmetry. Like conventional topological insulators and superconductors, TCIs and TCSCs support stable gapless boundary states associated with bulk topological nontriviality, when the additional symmetry is compatible with the boundary. Using the twisted equivariant K-theory, we complete the classification of TCIs and TCSCs in the presence of additional order-two nonsymmorphic space group (NSG) symmetry, which includes half lattice translation with $Z_2$ spin flip, glide, two-fold screw rotation, and their magnetic symmetries. From isomorphisms connecting different space dimensions, the K-groups are evaluated by those in one-dimension. The resultant topological table shows several interesting features: (1) The NSGs allow various $Z_2$ topological phases, even in the absence of time-reversal and/or particle-hole symmetries. Their boundary states are detached from the bulk spectrum in the direction of the non-primitive lattice translation. (2) $Z_4$ phases are found to be realized. Especially, the TCI with the glide and the time-reversal symmetry in three-dimensions shows the $Z_4$ phase. [Preview Abstract] |
Tuesday, March 15, 2016 3:30PM - 3:42PM |
H28.00004: Anion-Anion Bonding and Topology in Ternary Iridium Tin Selenides Benjamin Trump, Jake Tutmaher, Tyrel McQueen Iridium compounds have been under intense scrutiny due to strong relativistic effects (spin-orbit coupling) which have comparable energy scales to crystal field stabilization and electron correlations, which could lead to non-trivial behavior. Here we report the synthesis, characterization, and physical properties of two new, and one known, Ir-Sn-Se compounds. Resistivity, specific heat, and magnetization measurements show that all three have insulating and diamagnetic behavior, indicative of low spin 5d$^{\mathrm{6}}$ Ir$^{\mathrm{3+}}$. Furthermore, electronic structures calculations on Ir$_{\mathrm{2}}$Sn$_{\mathrm{3}}$Se$_{\mathrm{3}}$ show a single, spherical, non-spin-orbit split valence band that supports mobile p-type carriers, and imply that Ir$_{\mathrm{2}}$Sn$_{\mathrm{3}}$Se$_{\mathrm{3}}$ is topologically non-trivial under tensile strain, due to inversion of Ir-$d$ and Se-$p$ states. [Preview Abstract] |
Tuesday, March 15, 2016 3:42PM - 3:54PM |
H28.00005: Helical Quantum Edge Gears in 2D Topological Insulators Yang-Zhi Chou, Alex Levchenko, Matthew Foster A remarkable and as-yet-unexploited aspect of topological insulator (TI) physics is the topology of the edge states, i.e. the fact that the edge liquid of a 2D TI forms a closed, unbreakable loop in the absence of electrical contacts or magnetic fields. We propose a novel experimental setup in which edge loops rotate as interlocking “gears” through Coulomb drag, in TIs with Rashba spin-orbit coupling. We show that two-terminal transport can measure the Luttinger liquid parameter $K$, a quantity that is otherwise notoriously difficult to measure. In the low-temperature ($T \rightarrow 0$) perfect drag regime, the conductance is $(e^2/h)(2 K + 1)/(K + 1)$. At higher $T$ we predict a conductivity $\sim T^{-4K+3}$. Our results should trigger new experiments and may open a new venue for edge gear-based electronic devices.\\ Ref: Phys. Rev. Lett. 115, 186404 (2015) [Preview Abstract] |
Tuesday, March 15, 2016 3:54PM - 4:06PM |
H28.00006: Quantum anomalous Hall effect with field-tunable Chern number near Z$_2$ topological critical point Le Quy Duong, Hsin Lin, Wei-Feng Tsai, Yuan Ping Feng We study the practicability of achieving quantum anomalous Hall (QAH) effect with field-tunable Chern number in a magnetically doped, topologically trivial insulating thin film. Specifically in a candidate material, TlBi(S$_{1-\delta}$Se$_{\delta}$)$_2$, we demonstrate that the QAH phases with different Chern numbers can be achieved by means of tuning the exchange field strength or the sample thickness near the Z$_2$ topological critical point. Our physics scenario successfully reduces the necessary exchange coupling strength for a targeted Chern number. This QAH mechanism differs from the traditional QAH picture with a magnetic topological insulating thin film, where the ``surface'' states must involve and sometimes complicate the realization issue. Furthermore, we find that a given Chern number can also be tuned by a perpendicular electric field, which naturally occurs when a substrate is present.[1] High-Chern number QAH phase obtained from magnetically doped topological crystalline insulator thin films will also be discussed. \\ \\ REF: [1] Le Quy Duong, Hsin Lin, Wei-Feng Tsai, and Y. P. Feng, Phys. Rev. B 92, 115205 (2015). [Preview Abstract] |
Tuesday, March 15, 2016 4:06PM - 4:18PM |
H28.00007: Zero-field Dissipationless Chiral Edge Current in Quantum Anomalous Hall State Cui-Zu Chang, Weiwei Zhao, Duk Y. Kim, Peng Wei, J. K. Jain, Chaoxing Liu, Moses H. W. Chan, Jagadeesh S. Moodera The quantum anomalous Hall (QAH) state is predicted to possess, at zero magnetic field, chiral edge channels that conduct spin polarized current without dissipation, and thus holds great promise for future high-performance information processing. In this talk, we will discuss our transport experiments that probe the QAH state with gate bias and temperature dependences, by local and nonlocal magnetoresistance measurements. This allows us to unambiguously distinguish the dissipationless edge transport from transport via other dissipative channels in the QAH system. Our experiments confirm a fundamental feature of the QAH state, namely the dissipationless transport by edge channels in zero applied fields, which will be crucial for future chiral interconnected electric and spintronic applications. This research is supported by the NSF grants (DMR-1420620, Penn State MRSEC; in MIT by DMR-1207469 and the STC Center for Integrated Quantum Materials under NSF grant DMR-1231319) and by ONR Grant N00014-13-1-0301. [Preview Abstract] |
Tuesday, March 15, 2016 4:18PM - 4:30PM |
H28.00008: Anomalous Hall Effect on the surface of topological Kondo insulators Elio K\"onig, Pavel Ostrovsky, Maxim Dzero, Alex Levchenko We calculate the anomalous Hall conductivity $\sigma_{xy}$ of surface states on three dimensional topological Kondo insulators with cubic symmetry and multiple Dirac cones. We treat a generic model in which the Fermi velocity, the Fermi momentum and the Zeeman energy in different pockets may be unequal and in which the microscopic impurity potential is short ranged on the scale of the smallest Fermi wavelength. Our calculation of $\sigma_{xy}$ to the zeroth (i.e. leading) order in impurity concentration is based on the Kubo-Smrcka-Streda diagrammatic approach. It also includes certain extrinsic contributions with a single cross of impurity lines, which are of the same order in impurity concentration and were, to the best of our knowledge, scrutinized in a single band model, only. We discuss various special cases of our result and the experimental relevance of our study in the context of recent hysteretic magnetotransport data in SmB$_6$ samples. [Preview Abstract] |
Tuesday, March 15, 2016 4:30PM - 4:42PM |
H28.00009: Intrinsic Quantum Anomalous Hall Effect in the Kagome Lattice Cs2LiMn3F12 Gang Xu, Biao Lian, Shou-Cheng Zhang In a kagome lattice, the time reversal symmetry can be broken by a staggered magnetic flux emerging from the ferromagnetic ordering and intrinsic spin-orbit coupling, leading to several well-separated nontrivial Chern bands and intrinsic quantum anomalous Hall effect. Based on this idea and \textit{ab initio} calculations, we propose the realization of the intrinsic quantum anomalous Hall effect in the single layer Cs2Mn3F12 kagome lattice and on the (001) surface of a Cs2LiMn3F12 single crystal by modifying the carrier coverage on it, where the band gap is around 20 meV. Moreover, a simplified tight binding model based on the inplane dd$\sigma $ antibonding states is constructed to understand the topological band structures of the system. [Preview Abstract] |
Tuesday, March 15, 2016 4:42PM - 4:54PM |
H28.00010: Giant tunneling anomalous Hall conductance in topological insulators Alex Matos-Abiague, Benedikt Scharf, Jong E. Han, Ewelina M. Hankiewicz, Igor Zutic We theoretically investigate the tunneling transport across a magnetic barrier modulated by a top gate potential on the surface of a three-dimensional topological insulator. In the presence of a magnetization component along the bias direction, a finite tunneling anomalous Hall conductance (TAHC), transverse to the applied bias, develops. Depending on the strengths of the magnetization and gate potential, the system can exhibit a giant anomalous Hall angle, with the TAHC exceeding the longitudinal tunneling conductance. Moreover, we predict the existence of a negative differential TAHC even when the longitudinal differential conductance remains positive. [Preview Abstract] |
Tuesday, March 15, 2016 4:54PM - 5:06PM |
H28.00011: Effective boundary theory of the quantized thermal Hall effect Ryota Nakai, Shinsei Ryu, Kentaro Nomura We study the effective gravitational field theory that accounts for the quantized thermal Hall effect. The effective theory is microscopically derived from the one-dimensional massless boundary fermion, which is a manifestation of the two-dimensional bulk Dirac fermion with nontrivial energy band topology. The gravitational response of the boundary effective theory explains the bulk quantized thermal Hall effect through the Str\v{e}da formula. [Preview Abstract] |
Tuesday, March 15, 2016 5:06PM - 5:18PM |
H28.00012: Quantum tunneling between Chern states in a Topological Insulator Minhao Liu, Wudi Wang, Anthony R. Richardella, Abhinav Kandala, Jian Li, Ali Yazdani, Nitin Samarth, N. P. Ong The tunneling of a macroscopic object through a barrier is a quintessentially quantum phenomenon important in field theory, low-temperature physics and quantum computing. Progress has been achieved in experiments on Josephson junctions, molecular magnets, and domain wall dynamics. However, a key feature - rapid expansion of the true vacuum triggered by a tunneling event is virtually unexplored. Here we report the detection of large jumps in the Hall resistance Ryx in a magnetized topological insulator which result from tunneling out of a metastable topological state. In the TI, the conducting electrons are confined to surface Dirac states. When magnetized, the TI enters the quantum anomalous Hall insulator state in which Ryx is strictly quantized. If the magnetic field is reversed, the sample is trapped in a metastable state. We find that, below 145 mK, Ryx exhibits abrupt jumps as large as one quantum unit on time-scales under 1 ms. If the temperature is raised, the escape rate is suppressed consistent with tunneling in the presence of dissipation. The jumps involve expansion of the thermodynamically stable state bubble over macroscopic lengths, but dissipation limits the final size. The results uncover novel effects of dissipation on macroscopic tunneling. [Preview Abstract] |
Tuesday, March 15, 2016 5:18PM - 5:30PM |
H28.00013: Entanglement Spectra of Gapped One-dimensional Field Theories and Symmetry-Protected Topological Phases Gil Young Cho, Ken Shiozaki, Andreas Ludwig, Shinsei Ryu We discuss the entanglement spectrum(ES) of (1+1)d gapped Lorentz invariant field theories in the vicinity of a conformal field theory (CFT). In particular, for a gapped theory obtained by perturbing a CFT in infinite space by relevant perturbations, we show that the low-lying ES for the half-line is equal to the physical spectrum of the gapless CFT defined on a finite interval of length $L = \log (\xi/a)$, which is the spectrum of a boundary CFT. Here $\xi$ is the correlation length, $a$ a microscopic lattice scale, and our result applies in the "scaling limit" where $\xi\gg a$. A similar property has been known to hold for Baxter's Corner Transfer Matrices of a class of very special, namely integrable lattice models, for the entire ES and independent of the scaling limit. In contrast, our result applies to completely general gapped Lorentz invariant theories in the scaling limit, without the requirement of integrability, for the low-lying ES. As a consequence, while on a finite interval of length $2R$ the physical spectrum of the gapped theory is known to undergo a dramatic reorganization as $2R$ crosses $\xi$, the bipartite ES remains unchanged up to an overall scale. We apply these to (1+1)d symmetry-protected topological phases and symmetry-protected degeneracy of ES. [Preview Abstract] |
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