Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S44: Quantised Transport and Disorder in Kitaev MagnetsInvited Session
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Sponsoring Units: DCMP GMAG Room: BCEC 210C |
Thursday, March 7, 2019 11:15AM - 11:51AM |
S44.00001: Vison crystals in an extended Kitaev honeycomb model Invited Speaker: Gabor Halasz We introduce an extension of the Kitaev honeycomb model by including four-spin interactions |
Thursday, March 7, 2019 11:51AM - 12:27PM |
S44.00002: Field dependent magnetic excitations and possible topological transitions in α-RuCl3 Invited Speaker: Christian Balz It is now well-known that when a magnetic field of approximately 7.5 T is applied in the honeycomb plane, the quantum magnet α-RuCl3 displays a transition from zigzag magnetic order to a disordered state, believed to be a quantum spin liquid. This is reflected in the magnetic excitation spectrum as a disappearance of spin waves and a strengthening of a scattering continuum centered on the 2D Γ point that is interpreted as a signature of fractionalized excitations. Published measurements by Y. Kasahara et al (Nature 559, 227 (2018)) of the thermal Hall effect suggest a possible topological transition at an even higher field. Here I will discuss new high-resolution measurements of the excitations at fields spanning these two transitions. At the highest fields the broad scattering continuum is altered, and the response is seen to be dominated by a sharp peak at the lower bound, providing a strong indication that a new phase has been entered. The implications of these observations will be discussed in detail. |
Thursday, March 7, 2019 12:27PM - 1:03PM |
S44.00003: A spin–orbital-entangled quantum liquid on a honeycomb lattice Invited Speaker: Hidenori Takagi In 5d Ir4+ oxides, the spin-orbit coupling for 5d electrons is as large as ~0.5 eV and not small as compared with on-site Coulomb U. This often gives rise to a spin-orbital Mott state with Jeff=1/2 isospins [1]. In the family of insulating 5d Ir4+ oxides with a honeycomb-based structure, such as a-, b-, g-Li2IrO3 and Na2IrO3 (and also their 4d analogue a-RuCl3), Ir4+ ions are connected by the three orthogonal Ir-O2-Ir plane bonds, which gives rise to a bond-dependent Ising interactions among Jeff=1/2 isospins. These compounds were pointed out theoretically to be a materialization of Kiatev model with a topological spin liquid as the ground state [2, 3]. However, a long range magnetic ordering rather than a liquid state was observed in these compounds, likely due to the presence of magnetic interactions other than the Kitaev interactions. We recently visited a new generation of honeycomb iridates H3LiIr2O6, where all the interlayer Li+ ions in a-Li2IrO3 are replaced with H+, and discovered that a quantum spin liquid state is realized in H3LiIr2O6 [4]. H3LiIr2O6 does not show any trace of magnetic ordering down to 0.05 K, despite that an energy scale of magnetic interaction is ~ 100 K. We found at low temperatures below ~5K that the magnetization M, the NMR 1/T1 and the specific heat C are dominated by the contributions from spin defects and follows a scaling with B/T. After subtracting the scaled contribution from the defects, we find only T3-contribution in C(T) within the given resolution, which can be ascribed to the lattice contribution. This suggests the presence of a gap in the magnetic excitations. |
Thursday, March 7, 2019 1:03PM - 1:39PM |
S44.00004: The scale-invariant magnetic anisotropy of RuCl3 Invited Speaker: Kimberly Modic We present a detailed study of the magnetic anisotropy of RuCl3 – a layered honeycomb structure of effective spin-1/2 moments. The strong spin-orbit coupling of ruthenium enhances magnetic frustration, which leads to a zigzag antiferromagnetic (AFM) ground state at 7K – a temperature much lower than the exchange interaction energy scale. With magnetic fields of roughly 10 T, AFM order is suppressed and an unconventional spin state emerges. This state, characterized by an unsaturated magnetization, persists up to magnetic fields of order 100 T. We use a newly-developed technique – resonant torsion magnetometry – to explore the temperature evolution of the magnetic anisotropy in the high-field state of RuCl3. The high sensitivity of this technique allows us to measure a single crystallographic, and hence magnetic, domain. With increasing magnetic field, we observe a single transition associated with the suppression of AFM order. Above this transition, the magnetic anisotropy saturates (unlike the isotropic component of the magnetization), with a saturation field that scales linearly with temperature. Our data shows that the energy scale that determines the magnetic anisotropy is set only by field and temperature. This suggests that the intrinsic energy scale is driven to zero by strong correlations – a signature of a fluid-like spin state that is decoupled from the underlying exchange interactions. |
Thursday, March 7, 2019 1:39PM - 2:15PM |
S44.00005: Quantization of the thermal Hall conductivity at small Hall angles Invited Speaker: Mengxing Ye Recent experiments have described the measurement of a near-quantized thermal Hall conductance in α-RuCl3 as direct evidence for the propagation of a chiral Majorana mode in this system and consequently as smoking gun evidence for an intermediate chiral spin liquid phase in this system. However, the large experimental longitudinal thermal conductivity, attributed to bulk phonons, begs for an investigation of the spin-lattice coupling, and its role on the quantization of the thermal Hall conductivity. We show that due to the bulk and edge mixing of energy propagation, the temperature gradient of the bulk phonons develops a transverse component which may contribute to a quantized effective thermal Hall conductance. We also discuss the situations where the quantization breaks down and predict notable experiments that test it. |
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