Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C37: Spin Liquids: Alpha-RuCl3Focus
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Sponsoring Units: GMAG DCMP DMP Chair: Arnab Banerjee, Oak Ridge National Laboratory Room: BCEC 206A |
Monday, March 4, 2019 2:30PM - 3:06PM |
C37.00001: Kitaev spin liquids in spin-orbit coupled correlated materials Invited Speaker: Hae-Young Kee Recently, a new family of correlated honeycomb materials with strong spin-orbit coupling have been promising candidates to realize the Kitaev spin liquid. In particular, a half-integer quantized thermal Hall conductivity was reported in alpha-RuCl3 under the magnetic field. Using a generic nearest neighbour spin model with bond-dependent interactions, I will present numerical evidence of an extended regime of quantum spin liquids. I will also discuss how to achieve a chiral spin liquid near ferromagnetic Kitaev interaction in the presence of the magnetic field leading to the quantized thermal Hall conductivity. |
Monday, March 4, 2019 3:06PM - 3:18PM |
C37.00002: Field induced quantum spin liquid with spinon Fermi surfaces in the Kitaev model Hong-Chen Jiang, Changyan Wang, Biao Huang, Yuan-Ming Lu Recent experimental evidence for a field-induced quantum spin liquid (QSL) in α-RuCl3 calls for an understanding for the ground state of honeycomb Kitaev model under a magnetic field. In this work we address the nature of an enigmatic gapless paramagnetic phase in the antiferromagnetic Kitave model, under an intermediate magnetic field perpendicular to the plane. Combining theoretical and numerical efforts, we identify this gapless phase as a U(1) QSL with spinon Fermi surfaces. We also reveal the nature of continuous quantum phase transitions involving this U(1) QSL, and obtain a phase diagram of the Kitaev model as a function of bond anisotropy and perpendicular magnetic field. |
Monday, March 4, 2019 3:18PM - 3:30PM |
C37.00003: Magnetic field induced intermediate gapless spin-liquid phase with a spinon Fermi surface Niravkumar D. Patel, Nandini Trivedi Quantum spin liquids have generated considerable excitement in the condensed matter physics community. We employ the density matrix renormalization group to study the Kitaev model with a magnetic field in the H∥[111] direction. We show the presence of an intermediate phase, between the gapped Kitaev spin liquid and partially field polarized phase, that is a candidate spin liquid. We show that the spin-spin correlations in real-space obey power-law decay that is indicative of gapless spin excitations. Additionally, we present calculations of specific heat, entropy, and spin susceptibility at the finite temperature to provide further evidence of a gapless phase. Using the peaks of spin structure factor, we propose an existence of a spinon Fermi surface in the intermediate phase. |
Monday, March 4, 2019 3:30PM - 3:42PM |
C37.00004: Pristine graphene contacts to exfoliated α-RuCl3 crystals Jesse Balgley, Boyi Zhou, Paula J Kelley, David George Mandrus, Erik Henriksen The layered Mott insulator α-RuCl3 has garnered significant attention as a candidate to host a Kitaev quantum spin liquid, harboring fractionalized excitations and Majorana fermion-like spin excitations. Though significant progress has been made toward understanding how these phenomena manifest in α-RuCl3, experimental procedures to date have largely consisted of probes for pristine bulk samples. However a-RuCl3 may be readily exfoliated down to monolayer thicknesses. We show that we can achieve good electrical contact to α-RuCl3 using monolayer graphene, enabling direct measurement of the resistivity. In this talk, we present device configurations for interrogating exfoliated α-RuCl3 crystals in the few-layer limit by the fabrication of graphene/α-RuCl3 heterostructures. We further discuss measurements of the Mott gap via optical spectroscopy. |
Monday, March 4, 2019 3:42PM - 3:54PM |
C37.00005: Effect of pressure, stress and electronic modification on alpha-Rucl3 Sananda Biswas, Stephen Winter, Roser Valenti The honeycomb Mott insulator, α-RuCl3, is being intensively studied as a candidate for realizing Kitaev physics. One of the areas of current research is to find routes to enhance Kitaev interactions in order to stabilize a possible spin liquid, by increasing exchange frustration by the application of external perturbations such as magnetic field, doping or pressure. We have explored these possibilities by applying stress and electronic modifications. In this talk, I will discuss effects of these perturbations on structural, electronic, vibrational and magnetic properties. |
Monday, March 4, 2019 3:54PM - 4:06PM |
C37.00006: Raman spectroscopy evidence for dimerization and Mott collapse in α-RuCl3 under pressures Jiawei Mei We perform Raman spectroscopy studies on α-RuCl3 at room temperature to investigate its phase transitions of magnetism and structure under pressures. The Raman measurements resolve two critical pressures at p1=1.1 GPa and p2=1.7 GPa with very different structural and magnetic behaviors. With increasing pressure, a stacking order phase transition of α-RuCl3 occurs at p1, indicated by the inversion symmetry breaking and the appearance of new Raman modes. The second transition at p2 is signaled by the in-plane Ru-Ru bond dimerization accompanied by the Mott collapse, and the system becomes a correlated band insulator. Our studies demonstrate the competition among spin-orbit coupling, magnetism, and chemical bondings in Kitaev compounds. |
Monday, March 4, 2019 4:06PM - 4:18PM |
C37.00007: NMR observation of field induced fractionalized spin excitations in the Kitaev spin liquid candidate Yasuhiro Shimizu, Yuya Nagai, Takaaki Jinno, Masayuki Itoh, Junki Yoshitake, Joji Nasu, Yukitoshi Motome Quantum spin liquid involves fractionalized quasipariticles such as spinons and visons respectively corresponding to itinerant Majorana fermions and Z2 gauge fluxes in an exactcly soluble Kitaev model with frustrated bond-dependent exchange interactions on a honeycomb spin lattice. The observation has recently attracted attention for a candidate of the Kitaev model, α-RuCl3, showing spin liquid behaviour under magnetic field. Owing to the entanglement of these quasiparticles in magnetic observables, the identification remains challenging. Here we report nuclear magnetic and quadrupole resonance measurements down to 0.4 K [1]. Through the dynamical spin susceptibility in a low-energy limit, we found low-lying gapped excitations in two energy scales across the critical field where the magnetic order vanishes. The higher energy branch grows with a cubic field dependence, as expected for itinerant Majorana fermions, whereas the lower branch in an energy scale of the flux condensation appears above the critical field. The result suggests that the field induced mixing and redistribution of fractionalized excitations. |
Monday, March 4, 2019 4:18PM - 4:30PM |
C37.00008: Spin wave analysis of the Kitaev honeycomb magnet α-RuCl3 Seunghwan Do, Minseong Lee, J.H. Lee, Sang-Youn Park, David J. Voneshen, Kwang-Yong Choi, Jae-Hoon Park, Sungdae Ji The material α-RuCl3 has attracted great attention as a promising candidate for the 2D Kitaev honeycomb model. Due to its proximity to the Kitaev quantum spin liquid, various spectroscopic works on α-RuCl3 reveal both a magnetic continuum-like excitation suggestive of spin fractionalization and spin-wave-like modes from the antiferromagnetic order at low temperature. Despite numerous experimental and theoretical studies, magnetic excitations in the magnetically ordered state is not fully understood due to their complexity. In this talk, we provide a well describable picture of magnetic excitations in the magnetically ordered state of α-RuCl3 by using inelastic neutron scattering (INS) measurement. At the low temperature below TN (~6.5 K), the INS data shows sharp spin wave excitations distinguishable from the broad continuum. Our linear spin wave theory analysis identifies the spin wave modes and enable us to construct a minimal spin Hamiltonian of exchange interactions. By expanding spin wave analysis to higher order, we find that the spectral weight of continuum excitations is far beyond that of multi-magnon excitation. Furthermore, we present the field-dependence of magnetic excitation, and discuss about the possible field-induced quantum spin liquid state. |
Monday, March 4, 2019 4:30PM - 4:42PM |
C37.00009: New Features in the Field-dependent Thermal Conductivity of α-RuCl3 at Low Temperatures Peter Czajka, Tong Gao, Jingjing Lin, Paula J Kelley, Arnab Banerjee, Christian Balz, Jiaqiang Yan, David George Mandrus, Stephen Nagler, Nai-Phuan Ong α-RuCl3 is currently the most promising and well-studied candidate for realizing the unique physics of the Kitaev model. Because the energy scale of the exchange interactions is understood to be quite high (J ~ 100K), measurements at low temperatures have been somewhat scarce and it’s behavior below 2K remains largely unexplored. This is especially true for thermal transport experiments, which have proven to be an incredibly powerful probe of excitations and phase transitions in insulating magnets. We present measurements of the thermal conductivity as a function of temperature and in-plane magnetic field that were performed between 0.4 and 1.7K. We identify several new features in κxx(B) that occur between 7 and 11T, a regime located between the long range ordered and fully polarized states and where spin liquid behavior is thought to occur. Possible explanations for these new features as well as their relation to the recent observation of a half-integer quantized thermal hall conductance will be discussed. |
Monday, March 4, 2019 4:42PM - 4:54PM |
C37.00010: High Temperature Fermi Statistics from Majorana Fermions in an Insulating Magnet Yiping Wang, Gavin B Osterhoudt, Yao Tian, Paula J Kelley, Arnab Banerjee, Thomas A Goldstein, Jun Yan, Johannes Knolle, Joji Nasu, Yukitoshi Motome, Stephen Nagler, David George Mandrus, Kenneth Burch Majorana fermions, particles that are their own anti-particles, can emerge in insulating magnets as excitations with fractions of the constituent's quantum numbers. Interest in Majoranas is driven by their potential for quantum computation, and as evidence of novel topological states. Observations have been limited to liquid helium temperatures as edge modes in topological superconductors and quantum spin liquids (QSL) without combined evidence of particle-hole symmetry, Fermi statistics, and presence in the bulk. Here we report all three in α-RuCl3, at temperatures exceeding liquid nitrogen via new energy gain as well as loss Raman spectra and a unique framework to identify the statistical properties of the Kitaev QSL. α-RuCl3 is close to the Kitaev QSL, where bond-dependent Ising interactions produce excitations that are non-local in terms of spin flips. Consistent with particle-hole symmetric excitations obeying Paul-exclusion, the sum of the energy loss and gain responses are nearly temperature and energy independent. Our new method can be used to identify the unique properties of QSLs, and demonstrates the promise of α-RuCl3 for efforts in topological phases and quantum computation. |
Monday, March 4, 2019 4:54PM - 5:06PM |
C37.00011: Origin of the saw-tooth torque in spin-orbital-coupled magnets:
Application to α-RuCl3 Roser Valenti, Kira M. Riedl, Stephen Winter Honeycomb Kitaev candidate materials based on 4d5 and 5d5 metals have been recently shown to commonly display a distinct saw-tooth angular dependence of the magnetic torque over a wide range of magnetic fields. By a combination of density functional theory calculations, exact diagonalization and semiclassical considerations, we show here that bilinear anisotropic interactions and/or g-anisotropy are each sufficient to explain the observed torque response, which may be distinguished on the basis of high-field measurements. |
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