Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session F48: Frustrated Magnetism: Triangular LatticesFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Gregory MacDougall, University of Illinois Urbana-Champaign Room: 395 |
Tuesday, March 14, 2017 11:15AM - 11:51AM |
F48.00001: Z2 vortex crystals in triangular antiferromagnets with strong spin orbit coupling Invited Speaker: Ioannis Rousochatzakis The triangular-lattice Heisenberg antiferromagnet (HAF) is known to carry topological $Z_2$ vortex excitations which form a gas at finite temperatures. Here we show that the spin-orbit interaction, introduced via a Kitaev term in the exchange Hamiltonian, condenses these vortices into a triangular $Z_2$ vortex crystal at zero temperature. The cores of the $Z_2$ vortices show abrupt, soliton-like magnetization modulations and arise by a special intertwining of three honeycomb superstructures of ferromagnetic domains, one for each of the three sublattices of the 120$^\circ$ state of the pure HAF. This is a new example of a nucleation transition, analogous to the spontaneous formation of magnetic domains, Abrikosov vortices in type-II syperconductors, blue phases in cholesteric liquid crystals, and skyrmions in chiral helimagnets. As the mechanism relies on the interplay of geometric frustration and spin-orbital anisotropies, such vortex mesophases can materialize as a ground-state property in spin-orbit coupled correlated systems with nearly hexagonal topology, as in triangular or strongly frustrated honeycomb iridates. [Preview Abstract] |
Tuesday, March 14, 2017 11:51AM - 12:03PM |
F48.00002: Low energy electrodynamics of triangular lattice quantum spin liquid candidate YbMgGaO$_{4}$ xinshu zhang, Fahad Mahmood, Nicholas Laurita, Zhiling Dun, Haidong Zhou, Martin Mourigal, Peter Armitage Quantum spin liquids (QSL) are exotic magnetic states where spins do not order down to the lowest temperatures. Spin 1/2 two-dimensional triangular antiferromagnet YbMgGaO$_{4}$ is a promising QSL candidate. Here we report an optical measurement on YbMgGaO$_{4}$ using time domain terahertz spectroscopy (TDTS)and Fourier transform spectroscopy (FTIR). We find the real part of in-plane dissipative response shows a power law behavior that may arise from spin liquid properties. Applying magnetic field in the Faraday geometry, we approach the spin polarized state from which we can extract g-factors and determine exchange constants quantitatively. We also identify a crystal field excitation in the infrared measurement. Our results provide guidance for the future theoretical study of this QSL. [Preview Abstract] |
Tuesday, March 14, 2017 12:03PM - 12:15PM |
F48.00003: Chiral phase near quantum critical point Zhentao Wang, Oleg Starykh, Adrian Feiguin, Andrey Chubukov, Cristian Batista We study the sequence of quantum phase transitions between a quantum paramagnetic state and a magnetically ordered state for a 2D spin one triangular XXZ model with easy plane single-ion anisotropy $D S_z^2$. The mean field phase diagram of the model exhibits a direct transition between an XY antiferromagnetic state and a quantum paramagnetic phase (PM) induced by a large enough D value. The two phases are separated by a quantum critical point at $D=D_c$. The Ising-like $J_z$ interaction creates an attraction between quasiparticles of the quantum paramagnet with opposite spin. Upon approaching $D_c$ from the quantum paramagnetic side, we find that the resulting two-particle bound states condense before the single particle gap closes at $D=D_c$. This two-magnon bound state condensation signals the onset of a chiral liquid, which spontaneously breaks the inversion symmetry, while leaving the $U(1)$ symmetry intact. This leads to an emergent chiral liquid phase, which supports non-zero spin currents (vector spin chirality) without long range magnetic order. In our analytical treatment, the chiral phase appears for arbitrary small value of the Ising interaction. We further show evidence of the chiral phase by means of density matrix renormalization group calculations. [Preview Abstract] |
Tuesday, March 14, 2017 12:15PM - 12:27PM |
F48.00004: The origin of exciton mass in a frustrated Mott insulator Na$_2$IrO$_3$ Zhanybek Alpichshev, Edbert Sie, Fahad Mahmood, Gang Cao, Nuh Gedik We use a three-pulse ultrafast optical spectroscopy to study the relaxation processes in a frustrated Mott insulator Na$_2$IrO$_3$. By being able to independently produce the out-of-equilibrium bound states (excitons) of doublons and holons with the first pulse and suppress the underlying antiferromagnetic order with the second one, we elucidate the relaxation mechanism of quasiparticles in this system. By observing the difference in the exciton dynamics in the magnetically ordered and disordered phases, we found that the mass of this quasiparticle is mostly determined by its interaction with the surrounding spins. [Preview Abstract] |
Tuesday, March 14, 2017 12:27PM - 12:39PM |
F48.00005: Disorder in NiGa2S4 seen with Raman and infrared spectroscopy M. E. Valentine, T. Higo, S. Nakatsuji, D. Chaudhuri, N. P. Armitage, N. Drichko The crystal structure of NiGa$_{2}$S$_{4}$ contains a two dimensional triangular lattice of Ni$^{2+}$ (S = 1) ions where ferromagnetic nearest neighbor interactions and antiferromagnetic third nearest neighbor interactions lead to magnetic frustration which suppresses magnetic ordering down to at least 1.5K. We studied disorder and structural distortions in NiGa2S4 by Raman and IR spectroscopy on single crystals in the energy range of 10 to 600 cm$^{-1}$ which covers the full range of $\Gamma$-point optical modes and compared our results to DFT calculations for vibrational modes. In the Raman spectrum for temperatures below 300K, additional modes are observed between 250 and 450 cm$^{-1}$. These features have energies that coincide with IR vibrational modes which are Raman-forbidden based on the point group symmetry, suggesting a local loss of inversion symmetry. Also, we observe an increased line width of the phonons involving significant motion of the S atoms adjacent to Ni and responsible for superexchange interactions within the magnetic lattice. This suggests disorder of these atoms which may be the cause of the suppressed magnetic order and spin freezing observed. [Preview Abstract] |
Tuesday, March 14, 2017 12:39PM - 12:51PM |
F48.00006: Quantum phase transitions in Heisenberg $J_1-J_2$ triangular antiferromagnet in a magnetic field Mengxing Ye, Andrey Chubukov We present the zero temperature phase diagram of a large $S$ Heisenberg antiferromagnet on a frustrated triangular lattice with nearest neighbor ($J_1$) and next nearest neighbor ($J_2$) interactions, in a magnetic field. We show that the classical model has an accidental degeneracy for all $J_2/J_1$ and all fields, but the degeneracy is lifted by quantum fluctuations. We show that at large $S$, for $J_2/J_1 <1/8$, quantum fluctuations select the same sequence of three sublattice co-planar states in a field as for $J_2 =0$, and for $1/8$ $< J_2/J_1$ $<1$ they select the canted stripe state for all non-zero fields. The transition between the two states is first order in all fields, with the hysteresis width set by quantum fluctuations. We also study the model with arbitrary $S$, including $S=1/2$, near the saturation field by exploring the fact that near saturation the density of bosons is small for all $S$. We show that for $S >1$ the transition remains first order, with a finite hystresis width, but for $S=1/2$ and, possibly, $S=1$, there appears a new intermediate phase, likely without a spontaneous long-range order. [Preview Abstract] |
Tuesday, March 14, 2017 12:51PM - 1:03PM |
F48.00007: A Schwinger boson mean field study of the $J_1$-$J_2$ Heisenberg triangular-lattice quantum antiferromagnet Dag-Vidar Bauer, John Ove Fjaerestad We use Schwinger boson mean field theory to study the ground state of the spin-$S$ triangular-lattice Heisenberg model with nearest ($J_1$) and next-nearest ($J_2$) neighbor antiferromagnetic interactions, treating $\kappa=2S$ as a continuous parameter. We consider two spin liquid Ansatze whose magnetically ordered versions correspond to 120-degree order and a a collinear ''stripe" order, respectively. For $\kappa=1$ there is a direct transition between these ordered states as $J_2/J_1$ increases. Motivated by an argument that a smaller $\kappa$ may be more appropriate for describing the $S=1/2$ case qualitatively, we find that as one lowers $\kappa$, a spin liquid region eventually opens up between the ordered phases, in qualitative agreement with various recent numerical studies of the $S=1/2$ model. This picture suggests a symmetric gapped Z$_2$ spin liquid which is the disordered version of the 120-degree ordered state. [Preview Abstract] |
Tuesday, March 14, 2017 1:03PM - 1:15PM |
F48.00008: Evidence for a spinon Fermi surface in a triangular lattice quantum spin liquid candidate Yao Shen, Yao-Dong Li, Hongliang Wo, Yuesheng Li, Shoudong Shen, Bingying Pan, Qisi Wang, Helen Walker, Paul Steffens, Martin Boehm, Yiqing Hao, Diana Quintero-Castro, Leland Harriger, Matthias Frontzek, Lijie Hao, Siqin Meng, Qingming Zhang, Gang Chen, Jun Zhao In a quantum spin liquid (QSL), highly entangled spins remain disordered down to zero temperature due to strong frustration and quantum fluctuation. Such exotic quantum state can support fractionalized spin excitations called ‘spinon’. In this talk, we present neutron scattering measurements on a QSL candidate YbMgGaO$_4$, a highly frustrated antiferromagnet in which Yb ions form a quasi-two-dimensional triangular lattice. Broad spin excitations are revealed covering a wide region of the Brillouin zone which persists from the lowest measured energy to the zone boundary. The observed continuum is a key characteristic for spinon excitations, providing evidences for a QSL state in YbMgGaO$_4$ that has a spin-1/2 triangular lattice. [Preview Abstract] |
Tuesday, March 14, 2017 1:15PM - 1:27PM |
F48.00009: Variational wave functions for the $S=1/2$ Heisenberg model on the anisotropic triangular lattice: Spin liquids and spiral orders Luca F. Tocchio, Elaheh Ghorbani, Federico Becca By using variational wave functions and quantum Monte Carlo techniques, we investigate the complete phase diagram of the Heisenberg model on the anisotropic triangular lattice, where two out of three bonds have super-exchange couplings $J$ and the third one has instead $J'$. This model interpolates between the square lattice and the isotropic triangular one, for $J'/J \le 1$, and between the isotropic triangular lattice and a set of decoupled chains, for $J/J' \le 1$. We consider all the fully-symmetric spin liquids that can be constructed with the fermionic projective-symmetry group classification [Y. Zhou and X.-G. Wen, arXiv:cond-mat/0210662] and we compare them with the spiral magnetic orders that can be accommodated on finite clusters. Our results show that, for $J'/J \le 1$, the phase diagram is dominated by magnetic orderings, even though a spin-liquid state may be possible in a small parameter window, i.e., $0.7 < J'/J < 0.8$. In contrast, for $J/J' \le 1$, a large spin-liquid region appears close to the limit of decoupled chains, i.e., for $J/J' < 0.6$, while magnetically ordered phases with spiral order are stabilized close to the isotropic point. [1] E. Ghorbani, L.F. Tocchio, and F. Becca, PRB 93, 085111 (2016). [Preview Abstract] |
Tuesday, March 14, 2017 1:27PM - 1:39PM |
F48.00010: Quantum spin liquid states of the triangular Heisenberg-Kitaev model Matthias Punk, Pavel Kos We study quantum disordered ground states of the two dimensional Heisenberg-Kitaev model on the triangular lattice using a Schwinger boson approach. Our aim is to identify and characterize potential gapped quantum spin liquid phases that are stabilized by anisotropic Kitaev interactions. For antiferromagnetic Heisenberg- and Kitaev couplings we find three different symmetric $Z_2$ spin liquid phases, separated by two continuous quantum phase transitions. Interestingly, the gap remains finite throughout the transitions. We discuss how these spin liquid states are related to known ordered phases in the classical limit. [Preview Abstract] |
Tuesday, March 14, 2017 1:39PM - 1:51PM |
F48.00011: Mapping the Phase Diagram of RMM’O4 Compounds in Pursuit of the Coveted Quantum Spin Liquid state William Steinhardt, Casey Marjerrison, Yaohua Liu, Sachith Dissanayake, David Graf, Marcus Daum, Martin Mourigal, Sara Haravifard Recently the rare earth RMM’O4 systems (where R = rare earth, M and M’ = transition or main group) have been suggested as strong spin-orbit coupled quantum spin liquid candidates. In these systems, effective spin-half moments arising from odd numbers of electrons per unit cell lie on a planar, geometrically frustrated triangular lattice. We have synthesized large high-quality single crystals of a variety of these compounds using the optical floating zone technique. In this talk we present our recent x-ray and neutron scattering results at extreme environmental conditions as well as magnetization measurements, and discuss the induced quantum critical phenomena and the phase diagram for this family of materials as a function of site mixing, substitution, magnetic field, pressure, and temperature. [Preview Abstract] |
Tuesday, March 14, 2017 1:51PM - 2:03PM |
F48.00012: Field-induced decays in XXZ triangular-lattice antiferromagnets Pavel Maksimov, Mike Zhitomirsky, Alexander Chernyshev We investigate field-induced transformations in the dynamical response of the XXZ model on the triangular lattice that are associated with the anharmonic magnon coupling and decay phenomena. Detailed theoretical predictions are made for a close physical realization of the spin-$\frac12$ XXZ model, Ba$_3$CoSb$_2$O$_9$. We demonstrate that dramatic modifications in magnon spectrum must occur in low out-of-plane fields that are easily achievable for this material. The hallmark of the effect is a coexistence of the clearly distinct well-defined magnon excitations with significantly broadened ones in different regions of the ${\bf k}\!-\!\omega$ space. The field-induced decays are generic for this class of models and become more prominent at larger anisotropies and in higher fields. [Preview Abstract] |
Tuesday, March 14, 2017 2:03PM - 2:15PM |
F48.00013: Hidden Multipolar Orders of Dipole-Octupole Doublets on a Triangular Lattice Xiaoqun Wang, Yaodong Li, Gang Chen Motivated by the recent development in strong spin-orbit-coupled materials, we consider the dipole-octupole doublets on the triangular lattice. We propose the most general interaction between these unusual local moments. Due to the spin-orbit entanglement and the special form of its wavefunction, the dipole-octupole doublet has a rather peculiar property under the lattice symmetry operation. As a result, the interaction is highly anisotropic in the pseudospin space, but remarkably, is uniform spatially. We analyze the ground state properties of this generic model and emphasize the hidden multipolar orders that emerge from the dipolar and octupolar interactions. We clarify the quantum mutual modulations between the dipolar and octupolar orders. We predict the experimental consequences of the multipolar orders and propose the rare-earth triangular materials as candidate systems for these unusual properties. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700