Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S48: Frustrated Magnetism: Spin Liquids IIFocus

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Sponsoring Units: GMAG DMP Chair: Masaaki Matsuda, Oak Ridge National Lab Room: 395 
(Author Not Attending)

S48.00001: Experimental realization of a new quantum spin liquid. Bella Lake, Christian Batz, Johannes Reuther, Hubertus Luetkens, Rico Schönemann, Thomas Herrmannsdörfer, Yogesh Singh, A. T. M. Nazmul Islam, Elisa M. Wheeler, Jose A. RodriguezRivera, Tatiana Guidi, Giovanna G. Simeoni, Chris Baines, Hanjo Ryll Unlike conventional magnets where the magnetic moments are partially or completely static in the ground state, in a quantum spin liquid they remain in collective motion down to the lowest temperatures. Despite an extensive search among such compounds, experimental realizations remain very few. Here we investigate the new spin1/2 magnet, Ca$_{10}Cr$_{7}$O$_{28}$, which has a unexplored lattice with several isotropic interactions consisting of strong ferromagnetic and weaker antiferromagnetic couplings. Bulk properties measurements, neutron scattering and muon spin relaxation reveal coherent spin dynamics in the ground state, the complete absence of static magnetism and diffuse spinonlike excitations. Thus we show experimentally that it displays all the features expected of a quantum spin liquid. [Preview Abstract] 
Thursday, March 16, 2017 11:27AM  11:39AM 
S48.00002: Physical realization of a quantum spin liquid based on a complex frustration mechanism Johannes Reuther, Christian Balz, Bella Lake Unlike conventional magnets where the spins undergo magnetic longrange order in the ground state, in a quantum spin liquid they remain disordered down to the lowest temperatures without breaking local symmetries. Here, we investigate the novel, unexplored bilayerkagome magnet Ca$_{10}$Cr$_{7}$O$_{28}$, which has a complex Hamiltonian consisting of isotropic antiferromagnetic and ferromagnetic interactions where the ferromagnetic couplings are the dominant ones. We show both experimentally and theoretically that this compound displays all the features expected of a quantum spin liquid. In particular, experiments rule out static magnetic order down to 19mK and reveal a diffuse spinonlike excitation spectrum. Numerically simulating this material using the pseudo fermion functional renormalization group (PFFRG) method, we theoretically confirm the nonmagnetic ground state of the system and qualitatively reproduce the measured spin correlation profile. By tuning the model parameters away from those realized in Ca$_{10}$Cr$_{7}$O$_{28}$ we further show that the spinliquid phase is of remarkable stability. [Preview Abstract] 
Thursday, March 16, 2017 11:39AM  11:51AM 
S48.00003: Single Crystal Growth of Candidate Spin Orbital Liquid Iron Scandium Sulfide (FeSc$_2$S$_4$) Jennifer Morey, Christopher Pasco, Kemp Plumb, Benjamin Trump, Tyrel McQueen, Seyed Koohpayeh Iron scandium sulfide (FeSc$_2$S$_4$), a spinel of the form AB$_2$X$_4$, is a candidate spinorbital liquid which has been the subject of many experimental and theoretical studies. Experimental work on this material has been hindered by the lack of large high quality single crystals. We report the first successful growths of large single crystal specimens of this material and present measurements of the structure and physical properties of these, along with measurements on stoichiometric powders. These crystal growths enable a wide variety of measurements that have so far been impossible on this interesting spin orbital liquid candidate material. [Preview Abstract] 
Thursday, March 16, 2017 11:51AM  12:03PM 
S48.00004: Origin of quantum spin liquid phase in Ca$_{10}$Cr$_7$O$_{28}$ Han Yan, Rico Pohle, Ludovic Jaubert, Nic Shannon Ca$_{10}$Cr$_7$O$_{28}$ is a spin1/2 magnet with a Kagom\'ebilayer structure and complex competing interactions, which has recently been shown to support a quantum spin liquid state. In this talk we explore what can be learned about Ca$_{10}$Cr$_7$O$_{28}$ through a combination of analytic techniques, and classical Monte Carlo simulation. Despite the underlying complexity of the material, we find that the spin liquid in Ca$_{10}$Cr$_7$O$_{28}$ may admit of a deceptively simple explanation. [Preview Abstract] 
Thursday, March 16, 2017 12:03PM  12:15PM 
S48.00005: Spin orbital singlet system FeSc$_2$S$_4$ under pressure Alun Biffin, Dmitry Chernyshov, Emmanuel Canevet, Tom Fennell, Jonathan S. White, Rustem Khasanov, Hubertus Luetkens, Alois Loidl, Vladimir Tsurkan, Christian R\"{u}egg The role of orbital degrees of freedom in quantum magnets is receiving intense focus recently, with the understanding that spinorbit coupled systems can display physics qualitatively different from their spin only counter parts. An example is the spinorbital singlet (SOS) state, which can provide an alternative to the conventional spin and orbitally ordered groundstates of quantum magnets. In such a scenario, the relative strengths of the exchange interaction and spin orbit coupling parameters determine the low temperature structure, with the former preferring ordered moments and the latter a nonmagnetic singlet. Moreover the quantum critical point separating these two phases is rather unique in that it marks the onset of criticality in both the spin and orbital sectors. This SOS picture has recently been applied to FeSc$_2$S$_4$, where despite strong antiferromagnetic exchange between JahnTeller active Fe$^{2+}$ ions no experimental signature of spin or orbital order has been detected. Building on our previous neutron scattering measurements, we have used hydrostatic pressure in neutron scattering, muon spin rotation and xray diffraction measurements to probe the unique phase diagram of FeSc$_2$S$_4$. My talk will focus on the results and interpretation of these experiments [Preview Abstract] 
Thursday, March 16, 2017 12:15PM  12:27PM 
S48.00006: Static and Dynamic Magnetic Properties of $S =$ 1/2 Inequilateral DiamondChain Compounds $A_3$Cu$_3$AlO$_2$(SO$_4$)$_4$ ($A=$K, Rb, Cs) Katsuhiro Morita, Takanori Sugimoto, Takami Tohyama, Shigetoshi Sota, Hiroko Koorikawa, Masayoshi Fujihala, Setsuo Mitsuda In highly frustrated onedimensional quantum spin systems, there emerge various exotic ground states, such as gapless spinliquid and gapped singlet dimer phases. In a magnetic field, the systems exhibit magnetization plateaus because of frustration and quantum ﬂuctuations. In the previous study, we have made magnetic measurements of diamond spin chain compounds $A_3$Cu$_3$AlO$_2$(SO$_4$)$_4$ ($A =$ K, Rb, Cs) [1]. K$_3$Cu$_3$Al$_2$(SO$_4$)$_4$ does not show magnetic order down to 1.8K, indicating a possible spinliquid ground state. However, the exchange interactions are not specified, so that it has been unclear what kind of mechanism is responsible for the spin liquid state. We determine the exchange interactions by fitting the temperature dependence of the susceptibility for $A_3$Cu$_3$AlO$_2$(SO$_4$)$_4$ to the result of the exact diagonalization calculations for an 18spin diamond periodic chain. Based on the estimated exchange interactions in K$_3$Cu$_3$AlO$_2$(SO$_4$)$_4$, we predict the magnetization curve with the 1/3 plateau and inelastic neutron scattering spectrum by densitymatrix renormalization group (DMRG) calculations. [1] M. Fujihala $et. al$., J. Phys. Soc. Jpn. {\bf 84} 073702 (2015). [Preview Abstract] 
Thursday, March 16, 2017 12:27PM  1:03PM 
S48.00007: Quantum spin liquid and spin ice states in new pyrochlores. Invited Speaker: Romain Sibille Magnetic systems with competing interactions can adopt exotic ground states. A particularly promising class is that of the geometrically frustrated magnets, such as the A$_{\mathrm{2}}$B$_{\mathrm{2}}$O$_{\mathrm{7}}$ pyrochlores, in which unusual spin liquids appear. Some of these phases feature shortrange correlated states analogous to a Coulomb phase and give rise to emergent quasiparticle excitations. Although cases like the classical spin ice are reasonably well understood, the theoretical expectation is that quantum fluctuations lead to novel phases which are quantum spin liquids (QSLs). For instance, the quantum spin ice (QSI) is a generalization of the classical spin ice state to include quantum fluctuations, such that the effective theory becomes emergent quantum electrodynamics  the classical monopoles become coherent quantum quasiparticles, and a novel excitation playing the role of the photon appears. In this talk, I will present results on three novel materials with potential for QSL states. Each of them corresponds to a way to potentially strengthen the role of quantum fluctuations on the ground state properties of pyrochlore magnets. Firstly, I will demonstrate that, in Tb$_{\mathrm{2}}$Hf$_{\mathrm{2}}$O$_{\mathrm{7}}$, where a sizeable gap isolates the nonKramers ground state doublet at low temperature, a large amount of anion Frenkel disorder leads to quenched random crystal fields and disordered magnetic interactions. The detailed study of this material demonstrates that disorder can play a crucial role in preventing longrange magnetic order at low temperatures, and instead induces a stronglyfluctuating Coulomb spin liquid with defectinduced frozen magnetic degrees of freedom. Secondly, I will present results on another QSL candidate based on nonKramers ions, Pr$_{\mathrm{2}}$Hf$_{\mathrm{2}}$O$_{\mathrm{7}}$, which displays striking characteristics of the ferromagnetic correlations expected in a QSI. Finally, in the pyrochlore Ce$_{\mathrm{2}}$Sn$_{\mathrm{2}}$O$_{\mathrm{7}}$, where macroscopic measurements suggest an antiferromagnetic liquid ground state with quantum fluctuations, I will present results including the determination of the crystal field states of the Kramers Ce$^{\mathrm{3+}}$ ions in order to connect with recent theoretical proposals. [Preview Abstract] 
Thursday, March 16, 2017 1:03PM  1:15PM 
S48.00008: Strong SpinOrbit Coupling and Spin Liquids on the Triangular Lattice Jason Iaconis, Gabor Halasz, Chunxiao Liu, Leon Balents In recent years it has been realized that strong spinorbit coupling can provide a new avenue in the search for spin liquid phases in experimentally realizable materials. A powerful tool in the study of such materials is found by looking at the different fully projected fermionic parton wave functions which are consistent with the projective symmetry group classification. Additionally, triangular lattice spin systems have long been seen as promising candidates to host such highly entangled phases of matter. To this end, we look at the full class of distinct nonmagnetic variational wave functions which are allowed on the triangular lattice when only the lattice symmetries are preserved. We use both analytic and numerical techniques to study the behavior of such spin systems when the interactions are highly anisotropic. We will, in particular, look at the various competitive spin liquid states and discuss possible connections to experimental systems. [Preview Abstract] 
Thursday, March 16, 2017 1:15PM  1:27PM 
S48.00009: The U(1) Spin Liquids in a SpinOrbitCoupled Triangular Lattice Mott Insulator: the Projective Symmetry Group Analysis and Spectroscopic Study Gang Chen, YuanMing Lu, YaoDong Li Motivated by the recent progress on the spinorbitcoupled triangular lattice spin liquid candidate material YbMgGaO$_4$, we carry out a systematic projective symmetry group analysis of the candidate spin liquid ground states. Due to the spinorbit entanglement of the Yb$^{3+}$ $4f$ local moments, the space group symmetry operation transforms the position and the orientation of the local moments simultaneously, and hence brings new ingredients to the symmetry fractionalization and the projective realization in the candidate spin liquid phases. Based on the early proposal of the spinon Fermi surface U(1) spin liquid for YbMgGaO$_4$, we classify the U(1) spin liquid using the fermionic parton construction. We find eight U(1) spin liquids with distinct symmetry fractionalization patterns for the R$\bar{3}$m space group symmetry that is appropriate for YbMgGaO$_4$. The spectroscopic results are computed within the meanfield approximation for each U(1) spin liquid. The connection with the experiments in YbMgGaO$_4$ and the future directions are discussed. [Preview Abstract] 
Thursday, March 16, 2017 1:27PM  1:39PM 
S48.00010: Projective symmetry group classification of $Z_2$ spin liquids in a pyrochlore lattice Chunxiao Liu, Leon Balents The rare earth pyrochlore oxides R${}_2$M${}_2$O${}_7$ are a class of compounds that supports frustrated magnetism, and some of them are predicted to host a spin liquid state in presence of strong quantum effects. Propelled by this theoretical idea and recent experimental observations, we give a complete classification of $Z_2$ spin liquid states in the pyrochlore lattice formed by the rare earth R ions within the projective symmetry group approach. A list of mean field states is given to match the classically ordered phases, and the transitions into spin liquid states are analyzed. The effects of strong spinorbit coupling in the pyrochlore materials are also discussed. This study provides a clear map of phases of pyrochlore for future experiments and further variational MonteCarlo study of the spin liquid states in pyrochlore materials. [Preview Abstract] 
Thursday, March 16, 2017 1:39PM  1:51PM 
S48.00011: Fieldinduced behaviour in the spinliquid candidate \mbox{$\kappa$(ET)$_2$Cu$_2$(CN)$_3$}: The role of spinorbit coupling Kira Riedl, Stephen M. Winter, Roser Valenti Significant evidence has recently emerged for a quantum spin liquid (QSL) state in a number of triangluarlattice organics, such as $\kappa$(ET)$_2$Cu$_2$(CN)$_3$. However, recent $\mu$SR studies (1) showed evidence for a very small energy gap in the ground state, and magnetic fieldinduced anomalies that remain essentially unexplained. In particular, a sharp crossover was observed, accompanied by a significant increase of the magnetization critical exponent $\beta$. While this crossover was initially interpreted as an exotic quantum critical point(1), we argue that the consideration of SOC suggests a more conventional interpretation (2).In the organics, SOC manifests as anisotropic exchange, which results in spincanting through the DzyaloshinskiiMoriya (DM) interaction and introduces zerofield magnon or spinon gaps. Contrary to the assumption that SOC in organics is negligible due to light C, S, H atoms, we show that SOC can be relevant for the explanation of lowenergy properties.In particular, we argue that the lowfield response of the spin liquid is dominated by the DM interaction, and this leads directly to the observed crossovers.\\(1) F. Pratt et al, Nature {\bf 471}, 612 (2011).\\(2) S.M. Winter, K. Riedl, R. Valenti, arXiv:1610.05468 (2016). [Preview Abstract] 
Thursday, March 16, 2017 1:51PM  2:03PM 
S48.00012: Control of Localization of Spin Excitations in the Dilute Ising Magnet LiHo${}_{0.045}$Y${}_{0.955}$F${}_4$ D.M. Silevitch, T.F. Rosenbaum, G. Aeppli Collections of quantum mechanical spins with dipolar interactions exhibit a complex set of states and excitations due to the long range and alternating sign of the dipolar potential. These localized excitations can be separated from each other as well as the delocalized continuum by measuring a spectral “hole” in the ordinary response in the presence of a large amplitude pump whose detailed shape gives insight into couplings among excitations and between excitations and the continuum. We show that in a disordered Ising magnet, LiHo${}_{0.045}$Y${}_{0.955}$F${}_4$, the quality factor $Q$ for such holes can be as high as $10^5$. In addition, we can sweep the quantum mixing parameter through zero via either the amplitude of the ac pump or a static external transverse field. The zerocrossing is associated with a dissipationless response at the drive frequency. The identification of such a point where localized degrees of freedom are minimally mixed with their environment in a dense and disordered dipolar coupled spin system means that we can control the degree to which qubits emerging from strongly interacting manybody systems can be localized. [Preview Abstract] 
Thursday, March 16, 2017 2:03PM  2:15PM 
S48.00013: Quantum domain walls induce incommensurate supersolid phase on the anisotropic triangular lattice Sebastian Eggert, XueFeng Zhang, ShiJie Hu, Axel Pelster We investigate the extended hardcore BoseHubbard model on the triangular lattice as a function of spatial anisotropy with respect to both hopping and nearestneighbor interaction strength. At halffilling the system can be tuned from decoupled onedimensional chains to a twodimensional solid phase with alternating density order by adjusting the anisotropic coupling. At intermediate anisotropy, however, frustration effects dominate and an incommensurate supersolid phase emerges, which is characterized by incommensurate density order as well as an anisotropic superfluid density. We demonstrate that this intermediate phase results from the proliferation of topological defects in the form of quantum bosonic domain walls. Accordingly, the structure factor has peaks at wave vectors, which are linearly related to the number of domain walls in a finite system in agreement with extensive quantum Monte Carlo simulations. We discuss possible connections with the supersolid behavior in the hightemperature superconducting striped phase. [Preview Abstract] 
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