Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K24: Spin Liquids Theory and Application to MaterialsFocus

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Sponsoring Units: GMAG DMP Chair: Gang Chen, Fudan Univ Room: LACC 403A 
Wednesday, March 7, 2018 8:00AM  8:12AM 
K24.00001: Dirac and chiral quantum spin liquids on the honeycomb lattice in a magnetic field Bruce Normand, ZhengXin Liu Motivated by recent experimental observations in αRuCl3, we study the KΓ model on the honeycomb lattice in an external magnetic field. By a slaveparticle representation and Variational Monte Carlo calculations, we reproduce the phase transition from zigzag magnetic order to a fieldinduced disordered phase. The nature of this state depends crucially on the field orientation. For particular field directions in the honeycomb plane, we find a gapless Dirac spin liquid, in agreement with recent experiments on αRuCl3. For a range of outofplane fields, we predict the existence of a KalmeyerLaughlintype chiral spin liquid, which would show a quantized thermal Hall effect. 
Wednesday, March 7, 2018 8:12AM  8:24AM 
K24.00002: Magnetic Field Effect in the 2D JQ Model: Metamagnetism and Evidence for Deconfined Spinons Adam Iaizzi, Anders Sandvik We present a quantum Monte Carlo study of a 2D S=1/2 quantum magnet, the JQ model, which combines an antiferromagnetic Heisenberg exchange J and a competing fourspin interaction Q, mimicking the behavior of frustrated systems in a signproblemfree manner. We subject this model to an external magnetic field, building on our previous work in 1D [1]. We show metamagnetism (magnetization jumps to saturation) above a critical coupling ratio (Q/J)_{min}. At a different coupling ratio (Q/J)_{c}, the Néel order is destroyed and replaced with a longrangeordered valencebond solid. This transition is a deconfined quantum critical point described by spinons: fractionalized S=1/2 bosons [2]. At (Q/J)_{c} the specific heat of a fieldinduced BoseEinstein condensate of spinons is expected to exhibit anomalous linear temperature dependence [3]. Our quantum Monte Carlo simulations demonstrate that this prediction holds above a lower temperature bound set by a fieldinduced BKT transition. 
Wednesday, March 7, 2018 8:24AM  8:36AM 
K24.00003: Fragility of the Quantum Spin Liquid State: The Case of Organic Charge Transfer Salts Kira Riedl, Stephen Winter, Roser Valenti The geometrically frustrated organic charge transfer salts have proven to host a number of good candidates for quantum spin liquids (QSL). Although these compounds have been the subject of extensive experimental studies in the past, the theoretical explanation of their properties is in many cases still an open issue. One interaction that has been rarely considered to influence the QSL systems is spinorbit coupling, due to the light C, S, H atoms in organics. We previously suggested (1) that an effective staggered field, caused by DzyaloshinskiiMoriya interaction, can induce a critical response under magnetic field, if the QSL materials are close to magnetic order. Here, we predict how the critical response is reflected in a range of experiments, such as μSR, ESR, NMR and magnetic torque. We compare the predictions to recent experimental results on a number of candidate materials (24). The position of each material in the phase diagram determines hereby the critical response and the fragility of the QSL state with respect to field induced order (5). 
Wednesday, March 7, 2018 8:36AM  8:48AM 
K24.00004: Signatures of fractionalized quasiparticle excitations in the dynamical spinspin correlations of candidate quantum spinliquid ground states David Ronquillo, Nandini Trivedi Numerical signatures of the fractionalized quasiparticle excitations (FQE) of quantum spinliquid (QSL) ground states have recently been of interest given their experimental accessibility. Inelastic neutron scattering may reveal identifying characteristics of FQE in the dynamical structure factor [J. Knolle, et al. Phys. Rev. Lett. 112, 207203 (2014)], while measuring the heat capacity of candidate materials may show characteristic features of FQE’s via an analysis of a system’s entropy release [J. Nasu, et al. Phys. Rev. B. 92, 115122 (2015)]. Here, we introduce a new probe that unambiguously characterizes the FQE of QSL ground states. We theoretically study the spin dynamics of candidate QSL ground states, of various model Hamiltonians, on a variety of lattice geometries, and identify previously unknown signatures of their FQE’s. Numerical simulations carried out on finite sized clusters of the 2D Kitaev model on a honeycomb lattice reveal characteristic topological signatures of fractionalization in the time dependent spinspin correlations, in an externally applied magnetic field. We discuss how experimental probes may detect this signature in candidate materials. 
Wednesday, March 7, 2018 8:48AM  9:00AM 
K24.00005: Spinon Magnetic Resonance of Quantum Spin Liquids Zhuxi Luo, Ethan Lake, JiaWei Mei, Oleg Starykh We describe electron spin resonance in a quantum spin liquid with significant spinorbit coupling. We find that the resonance directly probes spinon continuum which makes it an efficient and informative probe of exotic excitations of the spin liquid. Specifically, we consider spinon resonance of three different spinon meanfield Hamiltonians, obtained with the help of projective symmetry group analysis, which model a putative quantum spin liquid state of the triangular rareearth antiferromagnet YbMgGaO4. The band of absorption is found to be very broad and exhibit strong van Hove singularities of single spinon spectrum as well as pronounced polarization dependence. 
Wednesday, March 7, 2018 9:00AM  9:12AM 
K24.00006: Josephson Current of Monopolar Spinons through a Quantum Spin Ice Junction Sho Nakosai, Shigeki Onoda Quantum spin liquids are novel states of magnetic materials exhibiting long range quantum entanglement and topological order. They are characterized by exotic quasiparticles called spinons carrying fractionalized spin quanta and by emergent gauge fields. In particular quantum spin ice system accommodates bosonic magnetic monopolar spinons coupled to analogous electromagnetic fields. It can host a U(1) quantum spin liquid as a monopole insulator and a Higgs ferromagnet as a monopole superconductor. Here, we demonstrate an interference phenomena of spinons producing monopole supercurrent. Two Higgs ferromagnets weakly linked by a U(1) quantum spin liquid generates "Josephson supercurrent" of monopoles across the junction. Due to the analogous Amp`ere's law, the current produces an electric polarization in the U(1) quantum spin liquid medium, which is expected to be experimentally observed. 
Wednesday, March 7, 2018 9:12AM  9:48AM 
K24.00007: Thermal Fractionalization in Kitaev Quantum Spin Liquids Invited Speaker: Yukitoshi Motome The quantum spin liquid is an exotic state in insulating magnets, where conventional magnetic ordering is suppressed down to the lowest temperature by quantum fluctuations. Among the salient features is the fractionalization of quantum spins into emergent quasiparticles, such as spinons. Despite tremendous efforts for several decades, it is hard to identify the clear evidence of spin fractionalization in real materials. Most of such efforts have been done for asymptotic behaviors toward zero temperature, but they remain elusive due to extrinsic contributions inevitable at low temperatures. We here discuss more versatile signatures of the spin fractionalization in a wider temperature range, by taking the honeycomb Kitaev model. The Kitaev model provides an exact ground state being a quantum spin liquid, in which spins are fractionalized into itinerant Majorana fermions and localized Z_{2} fluxes. The model has attracted much attention since it is experimentally relevant to magnetic insulators with strong spinorbit coupling, such as A_{2}IrO_{3} and αRuCl_{3}. Beyond the exact ground state, we have investigated the static and dynamical properties of the Kitaev model at finite temperature, by developing new numerical techniques based on a Majorana fermion representation. We have unveiled the fingerprints of spin fractionalization in the temperature and energy dependences of various physical observables, such as the specific heat, magnetic susceptibility, NMR relaxation rate, dynamical spin structure factor, Raman scattering, and thermal transport. We will discuss the results in comparison with recent experimental data for the candidate materials. For references, visit http://www.motomelab.t.utokyo.ac.jp/publicatione.html. 
Wednesday, March 7, 2018 9:48AM  10:00AM 
K24.00008: Quantum spin liquid in the semiclassical regime Ioannis Rousochatzakis, Yuriy Sizyuk, Natalia Perkins Quantum spin liquids have been at the forefront of correlated electron research ever since their original proposal in 1973, and the realization that they belong to the broader class of intrinsic topological orders, along with the fractional quantum Hall states. According to received wisdom, quantum spin liquids can arise in frustrated magnets with low spin S, where strong quantum fluctuations act to destabilize conventional, magnetically ordered states. Here we present a magnet that has a Z2 quantum spin liquid ground state already in the semiclassical, largeS limit. The state has both topological and symmetry related ground state degeneracy, and two types of gaps, a 'magnetic flux' gap that scales linearly with S and an 'electric charge' gap that drops exponentially in S. The magnet is described by the spinS version of the spin1/2 Kitaev honeycomb model, which has been the subject of intense studies in correlated electron systems with strong spinorbit coupling, and in optical lattice realizations with ultracold atoms. The results apply to both integer and halfinteger spins. 
Wednesday, March 7, 2018 10:00AM  10:12AM 
K24.00009: How many spin liquids are there in Ca_{10}Cr_{7}O_{28}? Rico Pohle, Han Yan, Nicholas Shannon Ca_{10}Cr_{7}O_{28} is a novel magnetic insulator with S=1/2 Cr^{5+} ions on a bilayer breathing–Kagome lattice. Exchange interactions in Ca_{10}Cr_{7}O_{28} are predominantly ferromagnetic, giving rise to a positive CurieWeiss temperature of 2.35 K. None the less, no magnetic order is observed down to 19 mK, making Ca_{10}Cr_{7}O_{28} an unusual example of a twodimensional quantum spin liquid. 
Wednesday, March 7, 2018 10:12AM  10:24AM 
K24.00010: Unification of pinchpoints and halfmoons in spin liquids Han Yan, Rico Pohle, Nicholas Shannon Pinchpoints — singularities in the momentum resolved structure factor — are arguably the most wellknown signature of a U(1) spin liquid. As observed in various 2D and 3D lattice models, they imply divergencefree constraint on its effective magnetic field. 
Wednesday, March 7, 2018 10:24AM  10:36AM 
K24.00011: Detecting Symmetry Fractionalization by Magnetic Impurities Biao Huang, YuanMing Lu In contrast to various symmetrybreaking orders in Landau's paradigm, quantum spin liquids are longrange entangled manyspin ground states that cannot be characterized by local order parameters. A longstanding question is how to unambiguously detect the fractionalized excitations in quantum spin liquids, such as spinons that carry half spin each. Here we show that Kondo impurities can be used to sharply distinguish different symmetry fractionalization of spinons in a gapped quantum spin liquid. We also show the sharp experimental signatures of these spin liquids in the presence of dilute magnetic impurities. 
Wednesday, March 7, 2018 10:36AM  10:48AM 
K24.00012: Dynamical Structure Factor of Z2 Topological Spin Liquid Guang Yu Sun, Yancheng Wang, Chen Fang, Meng Cheng, Yang Qi, ZiYang Meng Employing largescale quantum Monte Carlo simulations and the recently developed stochastic analytic continuation technique, we systematically investigate the dynamical information of in Z2 topological spin liquid realized in the BalentsFisherGirvin XXZ spin model. In particular, we for the first time observe the evolution of dynamical spinspin correlation functions, through the the continuous transitions from spin liquid to symmetry breaking phases. We find symmetry fractionalization of the vison excitations can be revealed from spectral information, and hence provide evidence for experimentally accessible detections of topological order and the associated symmetry fractionalization. 
Wednesday, March 7, 2018 10:48AM  11:00AM 
K24.00013: CoupledChain Constructions of Fracton Spin Liquids Gábor Halász, Timothy Hsieh, Leon Balents Fracton spin liquids are topologically ordered phases in three dimensions that go beyond the standard paradigm of topological order; they feature unconventional fractional excitations that are either completely immobile or only mobile along lowerdimensional subsystems, such as lines or planes. While there are several exactly solvable models of such fracton spin liquids, including Haah's cubic code and the Xcube model, these models are far from realistic as they involve interactions between many spins at the same time. In our work, we present a general coupledspinchain construction for realizing a large class of fracton spin liquids in more realistic models involving only twospin interactions. Furthermore, we demonstrate that these coupledspinchain constructions directly translate into generalized parton constructions and hence illuminate the physical properties of the corresponding fracton spin liquids. 
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