Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B37: Spin Liquids: Theory and ExperimentFocus
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Sponsoring Units: GMAG DCMP Chair: Fahad Mahmood, Johns Hopkins University Room: BCEC 206A |
Monday, March 4, 2019 11:15AM - 11:27AM |
B37.00001: Critical Spin Liquid versus Valence Bond Glass in Triangular Lattice Organic κ-(ET)2Cu2(CN)3 Kira M. Riedl, Roser Valenti, Stephen Winter The organic triangular-lattice antiferromagnet κ-(ET)2Cu2(CN)3 has been extensively discussed as a quantum spin liquid (QSL) candidate. Recently, an intriguing quantum critical behaviour was suggested from low-temperature B/T scaling of the magnetic torque experiments [1]. Through microscopic analysis of all anisotropic contributions, including Dzyaloshinskii-Moriya and multi-spin scalar chiral interactions, we highlight significant deviations of the experimental observations from a quantum critical scenario. Instead, we show that disorder-induced spin defects provide a comprehensive explanation of the low-temperature properties[2]. These spins are attributed to valence bond defects that emerge spontaneously as the QSL enters a valence bond glass phase at low temperature. This theoretical treatment is applicable to a general class of frustrated magnetic systems; similar scaling is also observed in the Kagome lattice antiferromagnet Herbertsmithite[3]. |
Monday, March 4, 2019 11:27AM - 11:39AM |
B37.00002: Charge Order without Spin Order in the Layered Frustrated Magnet κ-(BEDT-TTF)2Hg(SCN)2Cl Teresa Le, Andrej Pustogow, Hsin-Hua Wang, Yongkang Luo, Elena Gati, Michael Lang, Stuart E Brown There are several quasi two-dimensional materials which do not order magnetically, including a number of geometrically frustrated organic charge transfer salts. To investigate the interplay between charge order (which may affect the frustration) and magnetic order, we use 1H NMR spectroscopy to examine the magnetic properties of κ-(BEDT-TTF)2Hg(SCN)2Cl, which exhibits a first-order metal-insulator transition to a charge ordered state at TCO = 30K. The high-temperature metallic phase exhibits Fermi-liquid behavior with constant (T1T)−1, while the spin-lattice relaxation rate is subject to an abrupt enhancement at TCO and shows a standard paramagnetic response down to 2 K, below which the relaxation rates decrease as 1/T1 ~ T2. The smooth temperature dependence of T1 and the absence of changes in the NMR spectra rule out magnetic order down to 25 mK suggesting decoupling of the spin and charge degrees of freedom, while the CO is expecetd to reduce the frustration. These observations are discussed in the context of the ground state without magnetic order. Ongoing field-dependent measurements may elucidate whether the magnetic interactions are subject to 1D physics. |
Monday, March 4, 2019 11:39AM - 11:51AM |
B37.00003: Quantum valence bond ice and its relation to κ-H3(Cat-EDT-TTF)2 Masahiko Yamada, Yasuhiro Tada Motivated by the discovery of the coexistence of unfrozen spin and dipole fluctuations |
Monday, March 4, 2019 11:51AM - 12:03PM |
B37.00004: Effect of randomness on spin excitations in quantum spin liquid state of 1T-TaS2 Hinako Murayama, Yuki Sato, Tomoya Taniguchi, Ryo Kurihara, xiangzhuo xing, Shigeru Kasahara, Yuichi Kasahara, Masaro Yoshida, Yoshihiro Iwasa, Marcin Konczykowski, Yuji Matsuda Quantum spin liquid (QSL) is a novel state of matter where the ground states are quantum mechanically entangled and have several characteristic features, including fractional excitations. However, the nature of QSLs remains elusive. To tackle this problem, studying the effect of quenched disorder is of vital importance. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B37.00005: Spin-Liquid-Like State in the Triangular Lattice Antiferromagnet TbInO3 Min Gyu Kim, Barry L. Winn, Songxue Chi, Andrei T Savici, Jose A Rodriguez, Yanbin Li, Xianghan Xu, Jae Wook Kim, Sang-Wook Cheong, Valery Kiryukhin Unpolarized and polarized inelastic neutron scattering studies in single crystals of the triangular-lattice (TL) antiferromagnets TbInO3 and TbIn0.95Mn0.05O3 are reported. Broad gapless magnetic excitations are located at the TL Brillouin zone boundary. They show a weak enhancement near the M points at the lowest energies, and shift to the K points with increasing energy. At higher energies, a broad dispersing excitation branch, also centered at the zone boundary, is observed after a gap. No signs of magnetic order are found down to the temperatures 100 times smaller than the effective interaction energy given by the excitation bandwidth, indicating a very strong frustration. The fluctuating magnetic moment exceeds one half of the Tb3+ free-ion value and is confined to the TL plane. These observations strongly suggest a triangular-lattice-based spin liquid state in TbInO3. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B37.00006: Spin Dynamics of the Elemental Quantum Spin Liquid β-Mn Joseph Paddison, Ross Stewart Pure β-Mn is the only elemental metal that shows quantum spin-liquid-like behavior [1]. Its magnetic Mn atoms occupy a frustrated three-dimensional network of corner-sharing triangles. Unlike all other transition metals, β-Mn does not show long-range magnetic order to the lowest measured temperatures (~0.3 K). Instead, its magnetic response is dominated by strong antiferromagnetic spin fluctuations that persist up to room temperature and exhibit non-Fermi-liquid scaling [2]. |
Monday, March 4, 2019 12:27PM - 1:03PM |
B37.00007: Dynamical spin structure factor from a variational Monte Carlo perspective Invited Speaker: Federico Becca The spin dynamical structure factor is computed within a variational framework to study frustrated Heisenberg models in one and two dimensions. Starting from Gutzwiller-projected fermionic wave functions, the low-energy spectrum is constructed by considering two-spinon excitations. Benchmarks on the one-dimensional J1-J2 model are considered. Here, an excellent description of both the gapless and gapped (dimerized) phases is obtained [1]. In the square lattice, we obtain the distinctive spectral signatures of the transition between the Neel and the spin-liquid phases that takes place for J2/J1 ∼0.45. By increasing the frustration, the magnon excitation at q=(π,0) and (0,π) broadens, suggesting the tendency towards a spin fractionalization. In addition, its energy softens, indicating the presence of gapless states at the transition and within the spin-liquid phase [2]. On the triangular lattice, we assess the possibility to have the magnon decay, as suggested by using spin-wave approaches for non-collinear magnetic orders [3]. The evolution of the spin dynamical structure factor when approaching the magnetically disordered phase in presence of a next-nearest-neighbor coupling J2 is also included [4]. Preliminary calculations on the kagome lattice are also discussed. |
Monday, March 4, 2019 1:03PM - 1:15PM |
B37.00008: Spinon resonance of two-dimensional U(1) spin liquids with Fermi surface. Oleg Starykh, Leon Balents We investigate signatures of spin liquids with spinon Fermi surfaces in electron spin resonance experiments. We focus on the magnetic field (h) and temperature (T) dependence of the linewidth η of the resonance peak in the ESR absorption spectrum. We show that in the presence of DM interaction, the linewidth is determined by the low-energy U(1) gauge fluctuations resulting in a characteristic η ~ h2/3 scaling at T=0 and a more complicated behavior T/h + T2/3 f(h/T), with an explicit form of the scaling function f(x), at finite T. We find that exchange anisotropy results in a weaker h and T dependence of η. We discuss relevance of our findings to experiments on the spin liquid candidate κ-ET and related materials. |
Monday, March 4, 2019 1:15PM - 1:27PM |
B37.00009: Phenomenological Theory of Coulombic Quantum Spin Liquids Sangjin Lee, Eun-Gook Moon, SungBin Lee Coulombic quantum spin liquids (C-QSLs) whose low energy excitations are U(1) gauge fluctuations realize massive quantum entanglement in quantum magnets. They have been suggested to be hosted in several three-dimensional materials including a pyrochlore structure, A2B2O7. In this study, we present a phenomenological theory of C-QSLs and their phase transitions in the extended Landau paradigm. Within extended Landau paradigm which can be achieved by enlarging symmetry group, we obtain richer phase diagrams than the conventional order only diagrams. As a specific example, we construct the effective theory of conventional order parameters of a lattice symmetry(G) and emergent excitations of C-QSLs(~G) in the extended Landau paradigm. Namely, we write down all terms respecting a lattice symmetry and gauge invariance and investigate possible phase structures. For example, we apply our theory to systems with an all-in-all-out (AIAO) order parameter and U(1) gauge fluctuation dubbed Coulombic AIAO (AIAO*). Phenomenologically we obtain characteristic heat capacities and magnetic responses characterizing phases. Our theory may be directly applied to an insulating pyrochlore system where both A and B sites are magnetically active and one of them forms a U(1) quantum spin liquids. |
Monday, March 4, 2019 1:27PM - 1:39PM |
B37.00010: Classical and quantum phases of the J1-J2-J3 Heisenberg model on the body centered cubic lattice Pratyay Ghosh, Tobias Müller, Marlon Rück, Francesco Parisen Toldin, Rajesh Narayanan, Ronny Thomale, Johannes Reuther, Yasir Iqbal We present the global phase diagram of the Heisenberg model on the body-centered cubic (BCC) lattice with nearest-neighbor J1, second nearest-neighbor J2 and third nearest-neighbor J3 exchange couplings, for both antiferromagnetic and ferromagnetic J1, J2, and J3. The classical phase diagram is shown to host four commensurate magnetic orders [ferromagnet q=(0,0,0), Néel antiferromagnet q=(2π,0,0), q=(π,π,0), and q=(π,π,π)], and three incommensurate helimagnetic orders, namely, a one-, two- and three-dimensional spiral. The corresponding quantum spin-1/2 model is investigated employing the pseudofermion functional renormalization group (PFFRG) method. It is shown that quantum fluctuations (i) stabilize a quantum spin liquid phase over an appreciable region in parameter space centered around tri-critical points, (ii) strongly renormalize the phase boundaries (compared to those of the classical model), (iii) shift the pitch vector of the helimagnetic orders. We obtain the critical ordering temperatures for the S=1/2 model from Quantum Monte Carlo in the unfrustrated parameter regime, and compare it with the estimates obtained from one- and two-loop PFFRG. In the frustrated regime of the model, we compare our estimates with results available from other methods. |
Monday, March 4, 2019 1:39PM - 1:51PM |
B37.00011: Control of Magnetic and Topological Orders with a DC Electric Field Kazuaki Takasan, Masahiro Sato In this talk, we present our theoretical proposal which provides a new route to control magnetic and topological orders in a broad class of insulating magnets with a DC electric field [1]. We show from the strong-coupling expansion that magnetic exchange interactions along the electric-field direction are generally enhanced in Mott insulators. It indicates that we can control the spatial structure of the interactions in magnets with a DC electric field. To illustrate this idea, we particularly focus on two kinds of magnets, frustrated magnets and quasi-one-dimensional magnets, and obtain phase diagrams including several magnetic or topological ordered phases such as quantum spin liquids and Haldane-gap states. Our proposal is effective especially for magnets in the vicinity of quantum critical points, and would also be applicable for magnets under low-frequency AC electric fields such as terahertz laser pulses. Our result would pave a promising way to control the exotic states of matter in magnets. |
Monday, March 4, 2019 1:51PM - 2:03PM |
B37.00012: Construction of matrix product state for the Gutwiller projected variational wavefunctions Amir Mohammadaghaei, Bela Bauer, Kirill Shtengel, Ryan Mishmash An accurate description of various quantum spin liquid states using tensor network methods remains notoriously challenging. For large quasi-1D systems, the density matrix renormalization group and related methods usually require significant computational resources and sometimes fail to converge to a satisfactory state. On the other hand, variational wavefunctions acquired from the Gutzwiller projection of gaussian fermionic theories has long served as both a theoretical starting point for construction of such spin liquid states and as an inspiration for numerical variational Monte Carlo (VMC) to calculate observables of interest. In this work, we examine a different method by exploring the possibility of constructing a matrix product state (MPS) representation for a Gutzwiller-projected state from two given MPS representations of gaussian fermionic theories. We investigate the complexity of different approaches to achieve this goal and test the methods on two copies of a single half-filled band of spin-1/2 fermionic spinons. We then apply this method to two MPS of multi-band fermionic spinon theories in an attempt to describe spin liquid states on a quasi-1D strips of triangular and kagome-like lattices and compare to the complexity of the traditional VMC approach. |
Monday, March 4, 2019 2:03PM - 2:15PM |
B37.00013: Bridging partons and coupled-wire approaches to quantum spin liquids. Eyal Leviatan, David Mross Quantum spin systems which avoid symmetry-breaking order, e.g., due to geometric frustration, can instead form so-called quantum spin liquids. These phases, characterized by fractional excitations and emergent gauge fields, are thought to be realized in an increasing number of quasi-two-dimensional materials. In my talk, I will show how a wide range of gapped as well as gapless spin liquids can be accessed by a generalization of the ‘coupled-wire’ technique. In particular, I will construct explicit Hamiltonians that realize these phases and show how this method allows transparent access to subtle questions regarding the emergent gauge field, such as confinement. I will compare and contrast this approach to the popular parton-construction, and highlight the respective advantages. |
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