Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session E3: A New Approach to the Kitaev Quantum Spin LiquidInvited
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Sponsoring Units: GMAG DCMP Chair: Young-June Kim, Univ of Toronto Room: Ballroom III |
Tuesday, March 15, 2016 8:00AM - 8:36AM |
E3.00001: Possible Observation of fractionalized excitations in a Relativistic Mott Insulator Invited Speaker: Kenneth Burch The combination of electronic correlation and spin-orbit coupling is thought to precipitate a variety of highly unusual electronic phases in solids, including topological and quantum spin liquid states. I will discuss our recent optical measurements that provide evidence for the relativistic Mott Insulating ground state of $\alpha$-RuCl$_{3}$. Furthermore I will discuss the broad-continuum of scattering we observe, whose energy and temperature dependence suggest the presence of fractionalized excitations emerging from a quantum spin-liquid. [Preview Abstract] |
Tuesday, March 15, 2016 8:36AM - 9:12AM |
E3.00002: Inelastic neutron scattering evidence for Kitaev quantum spin liquid physics in $\alpha$-RuCl$_{3}$ Invited Speaker: Stephen Nagler The magnetic semiconductor $\alpha$-RuCl$_{3}$ is composed of very weakly coupled honeycomb layers of edge-sharing RuCl$_{6}$ octahedra. The Ru$^{3+}$ ion has 5 $d$ electrons in the low spin state, and the system is expected to have an effective $J=\frac{1}{2}$ single ion ground state with an interacting spin Hamiltonian containing Kitaev-like terms. Inelastic neutron scattering [1] on powders and single crystals has been used to determine the energy scale of the magnetic interactions and the overall form of the magnetic fluctuations. The results indicate that the Kitaev term is significant. Moreover, detailed measurements of the response show evidence for the fractionalized excitations that are characteristic of the Kitaev quantum spin liquid. $\\$[1] A. Banerjee $et \ al.$, arXiv:1504.08037. [Preview Abstract] |
Tuesday, March 15, 2016 9:12AM - 9:48AM |
E3.00003: Magnetic and Crystal Structure of $\alpha$-RuCl$_3$ Invited Speaker: Jennifer Sears The layered honeycomb material $\alpha$-RuCl$_3$ has been proposed as a candidate material to show significant bond-dependent Kitaev type interactions [1]. This has prompted several recent studies of magnetism in this material that have found evidence for multiple magnetic transitions in the temperature range of 8-14 K [2,3,4]. We will present elastic neutron scattering measurements collected using a co-aligned array of $\alpha$-RuCl$_3$ crystals, identifying zigzag magnetic order within the honeycomb planes with an ordering temperature of $\sim$8 K [2]. It has been reported that the ordering temperature depends on the c axis periodicity of the layered structure, with ordering temperatures of 8 and 14 K for three and two-layer periodicity respectively [3]. While the in-plane magnetic order has been identified, it is clear that a complete understanding of magnetic ordering and interactions will depend on the three dimensional structure of the crystal. Evidence of a structural transition at $\sim$150 K has been reported [4] and questions remain about the structural details, in particular the stacking of the honeycomb layers. We will present x-ray diffraction measurements investigating the low and high temperature structures and stacking disorder in $\alpha$-RuCl$_3$. Finally, we will present inelastic neutron scattering measurements of magnetic excitations in this material. \\[4pt] Work done in collaboration with K. W. Plumb (Johns Hopkins University), J. P. Clancy, Young-June Kim (University of Toronto), J. Britten (McMaster University), Yu-Sheng Chen (Argonne National Laboratory), Y. Qiu, Y. Zhao, D. Parshall, and J. W. Lynn (NCNR). \\[4pt] [1] K. W. Plumb et al., Phys. Rev. B 90, 041112(R) (2014). \\[0pt] [2] J. A. Sears et al., Phys. Rev. B 91, 144420 (2015). \\[0pt] [3] A. Banerjee et al., arXiv:1504.08037 (2015). \\[0pt] [4] Y. Kubota et al., Phys. Rev. B 91, 094422 (2015). [Preview Abstract] |
Tuesday, March 15, 2016 9:48AM - 10:24AM |
E3.00004: XY-like frustrated magnetic phase transitions in ${\alpha}$-RuCl$_3$ Invited Speaker: Hidekazu Tanaka It is known that a honeycomb-lattice antiferromagnet with the nearest-neighbor exchange interaction undergoes a conventional magnetic ordering even for the spin-1/2 case. However, when a certain amount of second-neighbor exchange interaction or anisotropic exchange interaction exists, the honeycomb-lattice quantum magnet exhibits an unusual ground state. In the last decade, spin-1/2 quantum magnets on honeycomb lattices have been attracting considerable attention from the viewpoints of the frustrated $J_1-J_2$ model and the Kitaev-Heisenberg model, both of which can exhibit the spin liquid state in some parameter range.\par $\alpha$-RuCl$_3$ is a layered compound, in which magnetic Ru$^{3+}$ ions with the $4d^5$ electronic state form a honeycomb lattice. We have investigated the magnetic properties of $\alpha$-RuCl$_3$ via magnetization and specific heat measurements using single crystals. It was observed that $\alpha$-RuCl$_3$ undergoes a structural phase transition at $T_{t}\,{\simeq}\,150$ K accompanied by fairly large hysteresis. The magnetizations and magnetic susceptibilities are strongly anisotropic, which mainly arise from the anisotropic $g$-factors. These $g$-factors and the obtained entropy indicate that the effective spin of Ru$^{3+}$ is one-half, which results from the low-spin state. Specific heat data show that magnetic ordering occurs in four steps at zero magnetic field. The magnetic phase diagram is obtained. The successive magnetic phase transitions can be ascribed to the competition among exchange interactions. We discuss the strongly anisotropic $g$-factors and deduce that the exchange interaction is strongly XY-like. Main results of this talk was published in Phys. Rev. B {\bf 91}, 094422 (2015). [Preview Abstract] |
Tuesday, March 15, 2016 10:24AM - 11:00AM |
E3.00005: Manifestations of Kitaev physics in thermodynamic properties of hexagonal iridates and $\alpha$-RuCl$_3$ Invited Speaker: Alexander Tsirlin Kitaev model is hard to achieve in real materials. Best candidates available so far are hexagonal iridates M$_2$IrO$_3$ (M = Li and Na) and the recently discovered $\alpha$-RuCl$_3$ featuring hexagonal layers coupled by weak van der Waals bonding. I will review recent progress in crystal growth of these materials and compare their thermodynamic properties. Both hexagonal iridates and $\alpha$-RuCl$_3$ feature highly anisotropic Curie-Weiss temperatures that not only differ in magnitude but also change sign depending on the direction of the applied magnetic field. N\'eel temperatures are largely suppressed compared to the energy scale of the Curie-Weiss temperatures. These experimental observations will be linked to features of the electronic structure and to structural peculiarities associated with deviations from the ideal hexagonal symmetry. I will also discuss how the different nature of ligand atoms affects electronic structure and magnetic superexchange. [Preview Abstract] |
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