Bulletin of the American Physical Society
APS March Meeting 2021
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session J46: Spin LiquidsLive

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Sponsoring Units: DCMP Chair: Alexander Wietek, Simons Foundation 
Tuesday, March 16, 2021 3:00PM  3:12PM Live 
J46.00001: Toric code topological order in a Rydberg blockaded model Ruben Verresen, Mikhail Lukin, Ashvin Vishwanath The physical realization of a quantum liquid with Z_{2} topological order as embodied in the paradigmatic toric code has proven to be an elusive goal. Here we demonstrate that this topological phase can be found in a twodimensional Rydberg atom array. In addition to identifying the phase in terms of the topological entanglement entropy and ground state degeneracies, we point out topological string operators that allow for a direct characterization. 
Tuesday, March 16, 2021 3:12PM  3:24PM Live 
J46.00002: Timedomain anyon interferometry in Kitaev honeycomb spin liquids and beyond Kai Klocke, David Aasen, Roger Mong, Eugene Demler, Jason F. Alicea Motivated by recent experiments on the Kitaev honeycomb magnet αRuCl_{3}, we introduce timedomain probes of the edge and quasiparticle content of nonAbelian spin liquids. Our scheme exploits ancillary quantum spins that communicate via timedependent tunneling of energy into and out of the spin liquid's chiral Majorana edge state. We show that the ancillaryspin dynamics reveals the edgestate velocity and, in suitable geometries, detects individual nonAbelian anyons and emergent fermions via a timedomain counterpart of quantumHall anyon interferometry. We anticipate applications to a wide variety of topological phases in solidstate and coldatoms settings. 
Tuesday, March 16, 2021 3:24PM  3:36PM Live 
J46.00003: Impurityinduced resonant spinon zero modes in Dirac quantum spin liquids Guangze Chen, Jose Lado Quantum spin liquids are strongly correlated phases of matter displaying a highly entangled ground state. Quantum spin liquids have attracted much research interest, in particular for their emergent Majorana physics and their longstanding relationship with unconventional superconductivity. Yet, due to their unconventional nature, finding experimental signatures of quantum spin liquids has proven to be a remarkable challenge. Here we show that magnetic S=1/2 impurities create resonant spinon zero modes in Dirac quantum spin liquids at zero energy. We show that the emergence of such zero modes is associated with the low energy Dirac nature of the spinon excitations, and we explore the interference effects between different impurity states. Finally, we show that the spinon zero modes result in a zero frequency divergence in the spin structure factor, that can be probed by inelastic spectroscopy and electricallydriven paramagnetic resonance. Our results highlight the dramatic effect of impurities in a Dirac quantum spin liquid, providing a stepping stone towards identifying Dirac quantum spin liquids through local real space measurement with scanning probe techniques. 
Tuesday, March 16, 2021 3:36PM  3:48PM Live 
J46.00004: Anisotropic magnetic interactions in Kitaev magnet YbCl_{3} Ravi Yadav, Satoshi Nishimoto, Sahinur Reja, Rajyavardhan Ray, Oleg Yazyev The prospect of realizing quantum spinliquid ground states in layered honeycomb materials with strong spinorbit interactions has triggered intense research activity in the condensed matter community [1]. Of particular interest is the Kitaev Hamiltonian on the honeycomb lattice [2]. In this work, we study the recently synthesized rareearth Kitaev magnet YbCl_{3}. Our manybody wavefunctionbased quantum chemistry calculations establish that this quasitwodimensional system is a highly anisotropic material with the anisotropy arising not only from magnetic exchange but also from ligand field on the Yb^{3+} ions. We find that the ground state is magnetically frustrated with an antiferromagnetic Kitaev exchange coupling, approximately four times as large as the isotropic Heisenberg couplings. By using exact diagonalization based on the generalized anisotropic effective Hamiltonian, we reveal a rich magnetic phase diagram with sizable second and third neighbor coupling stabilizing the system in a long range antiferromagnetic order, which is confirmed by experiments [3]. 
Tuesday, March 16, 2021 3:48PM  4:00PM Live 
J46.00005: Cavityinduced quantum spin liquids Alessio Chiocchetta, Dominik Kiese, Francesco Piazza, Sebastian Diehl Quantum spin liquids are the epitomes of highly entangled quantum states of matter. However, their detection in quantum materials remains elusive, due to the competition with more conventional magnetically ordered states. 
Tuesday, March 16, 2021 4:00PM  4:12PM 
J46.00006: 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 Z_{2} 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 nonAbelian 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 αRuCl_{3}, and would be distinguishable by their specific quantized values of the thermal Hall conductivity. 
Tuesday, March 16, 2021 4:12PM  4:24PM Live 
J46.00007: Unquantized thermal Hall effect in quantum spin liquids with spinon fermi surfaces Yunchao Zhang, Yanting Teng, Rhine Samajdar, Mathias Scheurer, Subir Sachdev Quantum spin liquids are of great interest because of their remarkable properties, including hosting fractionalized excitations and topological order. Recent theoretical studies have found quantum spin liquid states with spinon Fermi surfaces upon the application of a magnetic field on a gapped state with topological order. We investigate the thermal Hall conductivity across this transition, describing how the quantized thermal Hall conductivity of the gapped state changes to an unquantized thermal Hall conductivity in the gapless spinon Fermi surface state. We consider two cases, both of potential experimental interest: the state with nonAbelian Ising topological order on the honeycomb lattice, and the state with Abelian chiral spin liquid topological order on the triangular lattice. The thermal Hall conductivity is a powerful probe of the unconventional, chargeneutral excitations in these spin liquids, and our results bear direct relevance to recent experimental observations in the candidate Kitaev material, alphaRuCl3. 
Tuesday, March 16, 2021 4:24PM  4:36PM Live 
J46.00008: Fractional Excitation Induced Giant Phonon Anomalies in the Proximate Kitaev Quantum Spin Liquid aRuCl3 Haoxiang Li, Tiantian Zhang, Ayman Said, Gilberto F L Fabbris, Daniel Mazzone, Jiaqiang Yan, David George Mandrus, Gabor Halasz, Satoshi Okamoto, Shuichi Murakami, Mark Dean, Ho Nyung Lee, Hu Miao The Kitaev quantum spin liquid epitomizes an entangled topological state, for which two flavors of fractionalized lowenergy excitations are predicted: the itinerant Majorana fermion and the Z_{2} gauge flux. Detection of these excitations remains challenging, because of their fractional quantum numbers and nonlocality. It was proposed recently that fingerprints of fractional excitations are encoded in the phonon spectra of Kitaev quantum spin liquids through a novel fractionalexcitationphonon coupling. Here, we uncover this effect in aRuCl_{3} using inelastic Xray scattering with meV resolution. At high temperature, we discover interlaced optical phonons intercepting a transverse acoustic phonon between 3 and 7 meV. Upon decreasing temperature, the optical phonons display a large intensity enhancement near the Kitaev energy, J_{K}~8 meV, that coincides with a giant acoustic phonon softening near the Z_{2} gauge flux energy scale. This fractional excitation induced giant phonon anomalies uncover the key ingredient of the quantum thermal Hall effect in aRuCl_{3} and demonstrates a proofofprinciple method to detect fractional excitations in topological quantum materials. 
Tuesday, March 16, 2021 4:36PM  4:48PM Live 
J46.00009: Thermal Hall conductivity in the Kitaev spin liquid candidate αRuCl_{3} Etienne Lefrancois, Gael Grissonnanche, Adrien Gourgout, Paula J Kelley, Jiaqiang Yan, Christian Balz, David George Mandrus, Stephen E Nagler, Nicolas DoironLeyraud, Louis Taillefer The material αRuCl_{3} has been extensively researched as a potential candidate for Kitaev quantum spin liquid, whose lowenergy excitations are expected to be Majorana fermions. Note that αRuCl_{3} orders antiferromagnetically at low temperature, under T_{N }= 7 K, but an external magnetic field in the plane, greater than H_{∥} = 7 T, removes this order. The question is whether or not there is, over a range of fields greater than 7 T, an orderless region that harbours a liquid state of quantum spin. The recent announcement of a quantized thermal Hall conductivity κ_{xy} at H_{∥} > 7 T by Kasahara et al. [Kasahara et al., Nature 559, 227 (2018)] would be the first direct evidence of itinerant Majorana fermions in a quantum spin liquid state. In the study we present here, we examine the origin of κ_{xy} in αRuCl_{3}. The comparison between the longitudinal thermal conductivity κ_{xx} and κ_{xy} suggests that κ_{xy} is mainly dominated by phonons  questioning the possibility of a quantified κ_{xy}. In addition, depending on H_{∥}, we do not see an intermediate region between the antiferromagnetic state under 7 T and the state of polarized spins at strong magnetic field, thus leaving little room for a quantum spin liquid state. 
Tuesday, March 16, 2021 4:48PM  5:00PM Live 
J46.00010: The spin transport in a SU(2)symmetric chiral spin liquid model Zekun Zhuang, Brad Bradley Marston Chiral spin liquids are a class of spin liquids that break timereversal and parity symmetry. Yao and Lee proposed an exactly solvable SU(2) invariant spin1/2 model that is very similar to the Kitaev model except that there are three flavors of Majorana fermions coupled to a static gauge field. When timereversal symmetry is broken, this model supports a chiral spin liquid phase with chiral spin modes that exist on the boundary. I will discuss edge spin transport in the YaoLee model when sandwiched between two spin baths with different spin biases. I also consider the possibility that spin current noise in this system may provide a signature of this phase. 
Tuesday, March 16, 2021 5:00PM  5:12PM Live 
J46.00011: Phase diagram of the anisotropic triangular lattice Hubbard model Aaron Szasz, Johannes Motruk In our previous work [Phys. Rev. X 10, 021042 (2020)], we showed using density matrix renormalization group (DMRG) simulations on infinite cylinders that the triangular lattice Hubbard model with isotropic hopping hosts a chiral spin liquid phase at intermediate interaction strength. To better connect to experimental results in spin liquid candidate materials such as k(BEDTTTF)_{2}Cu_{2}(CN)_{3}, which are not precisely isotropic, in this work we add anisotropy to the model, making one of the three distinct bonds on the lattice stronger or weaker compared with the other two. We implement the anisotropy in two ways, one which respects the mirror symmetry of the cylinder and one which breaks this symmetry. Near the isotropic limit we find the three phases identified in our previous paper: an apparently metallic phase (which is possibly a LutherEmery liquid), the chiral spin liquid, and a phase with spiral magnetic order. When one bond is weakened by a relatively small amount, the ground state quickly becomes the square lattice Néel order. When one bond is strengthened, we find a large variety of interesting phases, with the specific ones that appear depending on the orientation of the anisotropy and on the cylinder circumference. 
Tuesday, March 16, 2021 5:12PM  5:24PM Live 
J46.00012: Fractionalized fermionic quantum criticality in spinorbital Mott insulators Urban Seifert, XiaoYu Dong, Sreejith Chulliparambil, Matthias Vojta, HongHao Tu, Lukas Janssen We study transitions between topological phases featuring emergent fractionalized excitations in twodimensional models for Mott insulators with spin and orbital degrees of freedom. 
Tuesday, March 16, 2021 5:24PM  5:36PM Live 
J46.00013: Spin liquids in open quantum systems Kang Yang, Siddhardh C Morampudi, Emil Bergholtz We establish the appearance of a qualitatively new type of spin liquid with emergent exceptional bandtouching behaviours when coupling to the environment. We consider an open system of the Kitaev model generically coupled to an external environment. In extended parameter regimes, the usual band crossings of the emergent Majorana fermions from the original model are split into exceptional band crossings. In glaring contrast to the original gapless phase of the honeycomb model which requires timereversal symmetry, this new phase is stable against all perturbations. The system also displays a large sensitivity to boundary conditions resulting from the nonHermitian skin effect with telltale experimental consequences. Our results point to the emergence of new classes of spin liquids in open systems which might be generically realized due to unavoidable couplings with the environment. 
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