Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session S55: Topology in Magnetic Systems |
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Sponsoring Units: DCMP Room: Mile High Ballroom 2B |
Thursday, March 5, 2020 11:15AM - 11:27AM |
S55.00001: Infinite Matrix Product States for Spin-Liquid Wavefunctions Gabriel Petrica, Bo-Xiao Zheng, Garnet Chan, Bryan Clark Quantum spin liquids are disordered ground states of interacting spin systems. As such they cannot be characterized by a local order parameter. Instead, entanglement measures, such as the entanglement spectrum and entanglement entropy, can be used to detect the presence of topological order. |
Thursday, March 5, 2020 11:27AM - 11:39AM |
S55.00002: Spinon Fermi surface in the Kitaev model induced by staggered magnetic field Jing-Yun Zhang, Hong Yao Kitaev model on the honeycomb lattice is an exactly solvable model of realizing quantum spin liquids which exhibits two distinct spin liquids in the parameter space: a gapped phase 'A' carries Z2 topological order and a gapless phase 'B' carries gapless fermions and gapped vortices. For the B phase, applying a uniform magnetic field would induce a gapped spin liquid phase with non- Ablelian anyons. In this talk, we will discuss the effect of a staggered external magnetic field in the B phase. We show that the original gapless Dirac cone spectra of fermions can be immediately turned into a finite spinon Fermi surface by a weak staggered field. Our analytical perturbative results are further supported by numerical computations. |
Thursday, March 5, 2020 11:39AM - 11:51AM |
S55.00003: A New Synthetic Quantum Spin Liquid Candidate CCO111 Xiaoran Liu, Sobhit Singh, Tomoya Asaba, Jess H Brewer, qinghua zhang, John William Freeland, Srimanta Middey, Mikhail Kareev, Dipankar Das Sarma, Padraic Shafer, Elke Arenholz, Lu Li, David Vanderbilt, Jak Chakhalian Quantum spin liquid is a new state of quantum strongly correlated topological matter characterized by the presence of a Mott gap, topological order and fictionalized spectrum of spin excitations. Despite the tremendous progress in bulk synthesis of potential QSL candidates the `smoking-gun' compound remains elusive. Here, we present a new synthetic candidate QSL material successfully templated from (111)-oriented CoCr2O4 by pulsed laser deposition. Remarkably, as the thickness is reduced to four Kagome-triangular atomic planes, the magnetic ground state suddenly switches from a spiral order to the quantum paramagnetic regime with no sign of long-range spin ordering down to 30 mK and 9T. At the same time, the frustration factor rises by almost three orders of magnitude indicating the first realization of a quantum spin liquid state on the new artificial lattice. Our findings open the opportunities of achieving novel ultra-quantum states of matter in a broad class of synthetic materials. |
Thursday, March 5, 2020 11:51AM - 12:03PM |
S55.00004: Dynamics of chiral spin liquids in the Kitaev-Yao-Kivelson model Bohai Li, Jing-Yun Zhang, Hong Yao Chiral spin liquid (CSL) is a type of quantum spin liquids which spontaneously break time reversal symmetry (TRS). For the exactly solvable Kitaev-Yao-Kivelson (KYK) model on the star lattice, the ground state is a CSL phase with either Abelian or non-Abelian anyons, depending on the parameters of the KYK model. We perform a theoretical study of the dynamical structure factor in both Abelian and non-Abelian phases of this model. Our result shows direct signatures of the Majorana fermions, vortex excitations, zero-energy modes of vortex excitations in the non- Abelian phase. |
Thursday, March 5, 2020 12:03PM - 12:15PM |
S55.00005: Z2 topological quantum spin liquids with only two-body Ising interactions and transverse fields Kai-Hsin Wu, Claudio Chamon, Anders W Sandvik In the recent study[1], the authors proposed a generalization of the transverse-field Ising model which can realize the Z2 gauge theory with only simple two-body interaction. The deconfined phase in the Z2 gauge model is the topologically ordered phase that is protected against any local perturbation. The model is also interesting in the sense that it can be implemented in the D-Wave Chimera-lattice structure. Here, we study the model using exact diagonalization and stochastic series expansion quantum Monte Carlo. We present our simulation results of the transition between the confined phase and deconfined phase that support the theoretical prediction. |
Thursday, March 5, 2020 12:15PM - 12:27PM |
S55.00006: Numerical evidence of a chiral spin liquid in the spin-1/2 honeycomb XY model Yixuan Huang, Xiaoyu Dong, Donna Sheng, Chin-Sen Ting The frustrated XY model on the honeycomb lattice has received lots of attentions because of the potential chiral spin liquid (CSL) in the intermediate region. Using density matrix renormalization group method on the cylinder system, we study the spin-1/2 XY model with first-neighbor (J1) and second-neighbor (J2) interactions, and in the presence of a chiral term. We obtain a quantum phase transition and a non-magnetic phase with finite scalar chiral order when we turn on a small chiral interaction. Further analysis of the entanglement spectrum is consistent with the Kalmeyer-Laughlin CSL in this region. |
Thursday, March 5, 2020 12:27PM - 12:39PM |
S55.00007: Toward Kitaev's Sixteenfold Way in a Honeycomb Lattice Model Shangshun Zhang, Cristian Batista, Gabor Halasz Kitaev's sixteenfold way is a classification of exotic topological orders in which Z2 gauge theory is coupled to Majorana fermions of Chern number C. The 16 distinct topological orders within this class, depending on C mod 16, possess a rich variety of Abelian and non-Abelian anyons. We realize more than half of Kitaev's sixteenfold way, corresponding to Chern numbers 0, ±1, ±2, ±3, ±4, and ±8, in an exactly solvable generalization of the Kitaev honeycomb model. For each topological order, we explicitly identify the anyonic excitations and confirm their topological properties. In doing so, we observe that the interplay between lattice symmetry and anyon permutation symmetry may lead to a "weak supersymmetry" in the anyon spectrum. The topological orders in our honeycomb lattice model could be directly relevant for honeycomb Kitaev materials, such as α-RuCl3, and would be distinguishable by their specific quantized values of the thermal Hall conductivity. |
Thursday, March 5, 2020 12:39PM - 12:51PM |
S55.00008: Finding the Generalized Gibbs Ensemble in the Real Space Entanglement Spectra of (2+1)-dimensional Chiral Topological Systems Mark Arildsen, Andreas W Ludwig The numerical calculation of entanglement spectra (ES) has become a useful way to diagnose topological properties of interesting many-body ground states. For (2+1)D quantum Hall states a correspondence between the low-lying levels of the ES across a given bipartition and of the physical spectrum of the edge states along the same cut was observed in Ref. [1]. When the ES of a chiral topological state is computed at a (finite) real space entanglement cut, however, we posit that additional physics should be visible in the splitting of the degeneracies of the low-lying energy levels arising from the presence of higher-order conserved quantities (irrelevant in the renormalization group sense) in the generalized Gibbs ensemble (GGE) associated to the theory on the edge. We analyzed the real space ES obtained in several previous numerical studies of (2+1)D chiral spin liquids with edges hosting (1+1)D conformal field theories possessing SU(2)-level-1 and SU(2)-level-2 symmetry. We fitted the splittings in these ES with sets of (irrelevant) conserved quantities and find that for the most part, we confirm their correspondence with the GGE picture outlined above. |
Thursday, March 5, 2020 12:51PM - 1:03PM |
S55.00009: Exchange Bias and Quantum Anomalous Hall Effect in the MnBi2Te4-CrI3 Heterostructure Huixia Fu, Chao-Xing Liu, binghai yan The layered antiferromagnetic MnBi2Te4 films have been proposed to be an intrinsic quantum anomalous Hall (QAH) insulator with a large gap. To realize this proposal, it is crucial to open a magnetic gap of surface states. However, recent experiments have observed gapless surface states, indicating the absence of out-of-plane surface magnetism, and thus the quantized Hall resistance can only be achieved at the magnetic field above 6 T. In this work, we propose to induce out-of-plane surface magnetism of MnBi2Te4 films via the magnetic proximity with magnetic insulator CrI3. Our calculations have revealed a strong exchange bias ~40 meV, originating from the long Cr-eg orbital tails that hybridize strongly with Te p-orbitals. By stabilizing surface magnetism, the QAH effect can be realized in the MnBi2Te4/CrI3 heterostructure. Our calculations also demonstrate the high Chern number QAH state can be achieved by controlling external electric gates. Thus, the MnBi2Te4/CrI3 heterostructure provides a promising platform to realize the electrically tunable zero-field QAH effect. |
Thursday, March 5, 2020 1:03PM - 1:15PM |
S55.00010: ARPES studies on antiferromagnetic topological insulators MnBi2nTe3n+1 Yong Hu, C.-F. Chen, Gang Xu, Xianhui Chen, Junfeng He The intrinsic magnetic topological insulators are believed to be an ideal platform for the study of various topological quantum phenomena, including the quantum anomalous Hall effect and topological magnetoelectric effect. Recently, a van der Waals layered structure, MnBi2Te4, was proposed to be the first intrinsic antiferromagnetic topological insulator. Furthermore, the related MnBi2nTe3n+1 (n=2,3) heterostructures are considered to be new magnetic topological insulators with weak interlayer magnetic coupling. In this talk, we report angle-resolved photoemission spectroscopy (ARPES) studies on a series of the heterostructures MnBi2nTe3n+1 (n=1,2,3). Our results reveal that the intrinsic magnetic topological insulators MnBi2nTe3n+1 host a rich platform to realize various novel topological states. |
Thursday, March 5, 2020 1:15PM - 1:27PM |
S55.00011: Surface state single Dirac cone in magnetic material GdxSb2-xTe3. Firoza Kabir, M. Mofazzel Hosen, Xiaxin Ding, Gyanendra Dhakal, Klauss Dimitri, Christopher Sims, Sabin Regmi, William Neff, Jian-Xin Zhu, Arjun K Pathak, Krzysztof Gofryk, Madhab Neupane Three-dimensional topological insulators (TI) have emerged as novel states in condensed matter physics. The surface states of a 3D TI are composed of odd number of massless Dirac cones in a Brillouin zone. The existence of these Dirac cones on the surface is characterized by the Z2 topological invariant. Strongly spin-orbit coupled material Sb2Te3 and most of its doped materials belong to the Z2 topological-insulator class. Using a combination of first-principles calculations, magneto transport properties and angle resolved photoemission spectroscopy (ARPES), we directly show that GdxSb2-xTe3 is a large spin-orbit-induced indirect bulk bandgap magnetic material whose surface is characterized by a single topological spin-Dirac cone. We demonstrate that the dynamics of spin Dirac fermions of Sb2Te3 can be controlled through Gd doping, making this magnetic material classes potentially suitable for topological device applications. |
Thursday, March 5, 2020 1:27PM - 1:39PM |
S55.00012: Photon energy and polarization dependent electronic structure of Cr doped Bi2Se3 thin films Turgut Yilmaz, Genda Gu, Elio Vescovo, Konstantine Kaznatcheev, Boris Sinkovic Here, we reported a comparison study of photon energy and photon polarization dependent electronic structure of Cr-doped and pristine Bi2Se3 to reveal the topological phase in transition metal doped topological insulators. Circular dichroism and photon energy dependent angle resolved photoemission experiment strongly confirm that the Cr doped samples have topologically non-trivial band structure. The surface electronic structure measurements with linear and circular polarized light show signature of the hybridization of the surface states and the impurity bands. Our observation not only provide further spectroscopic information about topological materials but also promotes additional experimental pathways to control the spin-orbital texture in topological materials. |
Thursday, March 5, 2020 1:39PM - 1:51PM |
S55.00013: Electronic structure of topological insulator Bi2Se3 thin films on thulium iron garnet heterostructures Sheng-Wen Huang, Keng-Yung Lin, Chun-Chia Chen, Mengxin Guo, Chao-Kai Cheng, Cheng-Maw Cheng, Minghwei Hong, Jueinai Kwo Breaking time-reversal symmetry (TRS) in topological insulator (TI) leads to exotic phenomena such as quantum anomalous Hall effect (QAHE). The novel phenomena originated from a gap opening at the Dirac surface state by exchange interaction with magnetic elements. Magnetically doped TI was first reported to exhibit such an exchange gap, but the observation temperature of QAHE was less than 2 K. Another way to break TRS is through interfacial magnetic proximity effect (MPE) in TI/ferromagnetic insulator bilayer with a strong ferromagnetism and uniform interfacial magnetization. In this work, TI films Bi2Se3 were grown by molecular beam epitaxy on ferromagnetic thulium iron garnet (TmIG) with perpendicular magnetic anisotropy and high TC above 500K. The band structures of 2-6 quintuple layer (QL) Bi2Se3/TmIG bilayers were investigated by angle-resolved photoemission spectroscopy. Comparative study in 2-6 QL Bi2Se3/sapphire was also performed. The energy gap opening at the surface state of Bi2Se3/TmIG is larger than that of Bi2Se3/sapphire by about 20 meV. The larger surface state gap of Bi2Se3/TmIG could be induced by MPE, on top of hybridization of top and bottom surfaces. Our study demonstrates the opportunity of probing interfacial band of TI-based heterostructures. |
Thursday, March 5, 2020 1:51PM - 2:03PM |
S55.00014: Path to building quantum spin liquids and topological qubits within existing quantum hardware Zhicheng Yang, Dmitry Green, Claudio Chamon We address a central problem in the creation and manipulation of quantum states: how to build topological quantum spin liquids with physically accessible interactions. Theorists have been studying models of quantum spin liquids that rely on ``multi-spin" interactions since the 1970s, and, more recently, have realized that these models can be used for quantum computing. However, nature does not provide such interactions in real materials. We construct a lattice gauge model where the required, fully quantum, multi-spin interactions can in fact be emulated exactly in any system with only two-body Ising interactions plus a uniform transverse field. The latter systems do exist, and we provide an explicit embedding of our model into one such system, the commercially available D-Wave machine. Therefore, our solution is an alternative path to building a workable topological quantum computer within existing hardware. Our bottom-up construction is generalizable to other gauge-like theories, including those with fractonic topological order such as the X-cube model. Taken as a whole, our approach is a blueprint to emulate topologically ordered quantum spin liquids in programmable quantum machines. |
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