Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A37: Kitaev MagnetismFocus
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Sponsoring Units: GMAG DCMP DMP Chair: Zheng-Xin Liu, Renmin University of China Room: BCEC 206A |
Monday, March 4, 2019 8:00AM - 8:36AM |
A37.00001: Gapless Visons and Emergent U(1) Spin Liquid in Kitaev's Honeycomb Model Invited Speaker: Ciarán Hickey In the field of quantum magnetism, the exactly solvable Kitaev honeycomb model serves as a paradigm for the fractionalization of spin degrees of freedom and the formation of Ζ2 spin liquid ground states. An intense experimental search has led to the discovery of a number of spin-orbit entangled Mott insulators that realize its characteristic bond-directional spin interactions and, in the presence of strong magnetic fields, exhibit no indications of long-range magnetic order. Here, we map out the complete phase diagram of the Kitaev model in tilted magnetic fields and report the emergence of a distinct gapless quantum spin liquid at intermediate field strengths. Analyzing a number of static, dynamical, and finite temperature quantities using numerical exact diagonalization techniques, we find strong evidence that this phase exhibits gapless fermions coupled to a massless gauge field resulting in a dense continuum of low-energy states. Such a phase can be naturally understood within the framework of Abrikosov fermionic partons as a U(1) quantum spin liquid with a spinon Fermi surface, emerging via a superconductor-metal transition. Finally, we discuss its stability in the presence of perturbations, Heisenberg and off-diagonal symmetric exchange interactions, that naturally arise in spin-orbit entangled Mott insulators alongside Kitaev interactions. |
Monday, March 4, 2019 8:36AM - 8:48AM |
A37.00002: Ground State of the Spin-1/2 Honeycomb Γ Model: Zigzag Magnetic Order Hai-Jun Liao, RuiZhen Huang, Yi-Bin Guo, Zhi-Yuan Xie, Bruce Normand, Tao Xiang The off-diagonal symmetric interaction, Γ ( Siα Sβi+γ + Siβ Sαi+γ ), has sprung to prominence |
Monday, March 4, 2019 8:48AM - 9:00AM |
A37.00003: Nonlinear magnetic susceptibility in the Kitaev model Yoshitomo Kamiya, Junki Yoshitake, Yasuyuki Kato, Joji Nasu, Yukitoshi Motome We study the nonlinear spin susceptibility in the Kitaev model [1]. The model has been serving as a paradigmatic model for studying a quantum spin liquid and extensive experimental efforts are currently undertaken. While the Jackeli-Khaliullin mechanism [2] predicts the ferromagnetic Kitaev model, recent theoretical studies suggest that the antiferromagnetic Kitaev model may stabilize distinct spin liquids in a magnetic field. Since the determination of the sign of the Kitaev coupling can be experimentally problematic, we propose a convenient complementary experimental signature to distinguish the two cases. Here, in the gapped spin liquid phase, we derive an analytical expression in perturbation theory and find that the nonlinear spin susceptibility exhibits a characteristic sign change at finite temperature in the ferromagnetic Kitaev model. We also present results based on numerical simulations (exact diagonalization and quantum Monte Carlo simulations), with which we show that the characteristic sign change also appears in the gapless spin liquid phase with a ferromagnetic coupling [3]. |
Monday, March 4, 2019 9:00AM - 9:12AM |
A37.00004: Ground-state phase diagram of the extended Kitaev-Heisenberg model on a honeycomb lattice Sei-ichiro Suga, Takafumi Suzuki, Takuto Yamada Recent studies on 4d and 5d transition-metal compounds on honeycomb lattices have unveiled possibility of realizing the Kitaev spin liquid. In this study, we consider the Kitaev-Heisenberg-Γ model on a honeycomb lattice, where symmetric-anisotropic interactions (Γ) exist in addition to the Kitaev and Heisenberg interactions. According to ab-initio calculations, this model describes the magnetism in spin-orbit-coupled honeycomb-lattice Mott insulators. We calculate the ground–state energy using series expansions, and obtain the phase diagram. This method has an advantage that can deal with infinite-size systems. We discuss our results by comparing them with the results so far obtained with various numerical methods [1-3]. [1] J. G. Rau, et al., Phys. Rev. Lett. 112, 077204 (2014). [2] A. Catuneanu, et al., npj Quantum Materials 3, 23 (2018). [3] M. Gohlke, et al., Phys. Rev. B 97, 075126 (2018). |
Monday, March 4, 2019 9:12AM - 9:48AM |
A37.00005: Dynamical and Topological Signatures of the Kitaev-Model in a [111] Magnetic Field Invited Speaker: Matthias Gohlke Quantum spin-liquids represent exotic phases of matter that host emergent fractionalized excitations. The Kitaev model [1] is a two-dimensional model system in this context and relevant for recent experiments on putative quantum spin-liquid materials. Here, we present results for the Kitaev model coupled to a magnetic field along the [111] axis. Using infinite DMRG, we confirm three phases with vastly different transition fields depending on the sign of the Kitaev exchange [2]: A topological phase hosting non-abelian anyons at low fields, an intermediate regime only existing for antiferromagnetic Kitaev exchange, and a field-polarized phase hosting topological magnons [3]. |
Monday, March 4, 2019 9:48AM - 10:00AM |
A37.00006: Field-induced neutral Fermi surface and QCD3 quantum criticalities in Kitaev materials Liujun Zou, Yin-Chen He We perform both numerical and theoretical studies on the phase diagram of the Kitaev materials in the presence of a magnetic field. We find that a new quantum spin liquid state with neutral Fermi surfaces emerges at intermediate field strengths, between the regimes for the non-Abelian chiral spin liquid state and for the trivial polarized state. We discuss the exotic field-induced quantum phase transitions from this new state with neutral Fermi surfaces to its nearby phases. We also theoretically study the field-induced quantum phase transitions from the non-Abelian chiral spin liquid to the symmetry-broken zigzag phase and to the trivial polarized state.Utilizing the recently developed dualities of gauge theories, we find these transitions can be described by critical bosons or gapless fermions coupled to emergent non-Abelian gauge fields, and the critical theories are of the type of a QCD$_3$-Chern-Simons theory. We propose that all these exotic quantum phase transitions can be direct and continuous in the Kitaev materials. Therefore, besides being systems with intriguing quantum magnetism, Kitaev materials may also serve as table-top experimental platforms to study the interesting dynamics of emergent strongly interacting quarks and gluons in $2+1$ dimensions. |
Monday, March 4, 2019 10:00AM - 10:12AM |
A37.00007: Formation of magnetic order in the Kitaev-Heisenberg model Shang-Shun Zhang, Gabor Halasz, Wei Zhu, Cristian Batista We compute the low-energy excitation spectrum and the dynamical magnetic spin structure factor of the Kitaev-Heisenberg model using a variational approach, that becomes exact at the exactly solvable Kitaev points. This approach reveals the physical origin of the asymmetry in the stability range of Kitaev spin liquid phases around the ferromagnetic and antiferromagnetic Kitaev points. We also show that bound states of fractionalized excitations appear in the proximity of a quantum phase transition between the ferrmagnetic Kitaev spin spin liquid and the magnetically ordered states induced by ferro and antiferromagnetic Heisenberg interactions. |
Monday, March 4, 2019 10:12AM - 10:24AM |
A37.00008: Quantum phases in spin-1 honeycomb antiferromagnets: application to Ni2Mo3O8 Shuyi Li, Vaideesh Loganathan, Wenjun Hu, Andriy Nevidomskyy Ni2Mo3O8 is a recently synthesized material containing spin-1 moments on a honeycomb lattice [1]. Such systems are of interest due to their potential to exhibit topological magnons. According to the recent neutron scattering experiment [1], the two sub-lattices making up the bipartite honeycomb lattice each display a zig-zag antiferromagnetic order. Moreover, the order is non-coplanar with a non-trivial angle between adjacent spins due to competing interactions. In this work, we attempt to explain this spin ordering by the means of mean-field theory and Density Matrix Renormalization Group (DMRG) calculations. We use ab initio Density Functional Theory (DFT) calculations to extract the spin-exchange coefficients in the effective low-energy model. We propose that the Dzyaloshinskii-Moriya interaction is the most natural way to explain the observed magnetic ordering. |
Monday, March 4, 2019 10:24AM - 10:36AM |
A37.00009: WITHDRAWN ABSTRACT
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Monday, March 4, 2019 10:36AM - 10:48AM |
A37.00010: Nonlocal String Order Parameter in the S=1/2 Kitaev-Heisenberg Ladder Erik Sorensen, Hae-Young Kee, Andrei Catuneanu We study the S=1/2 Kitaev-Heisenberg (KJ) model in a two-leg ladder. Without a Heisenberg interaction, the Kitaev phase in the ladder model has Majorana fermions with local Z2 gauge fields and is usually described as a disordered phase without any order parameter. Here we prove the existence of a non-local string order parameter (SOP) in the Kitaev phase which survives with a finite Heisenberg interaction. The SOP is obtained by relating the Kitaev ladder, through a non-local unitary transformation, to a one-dimensional XY chain with an Ising coupling to a dangling spin at every site. This differentiates the Kitaev phases from other nearby phases including a rung singlet. Two phases with non-zero SOP corresponding to ferromagnetic and antiferromagnetic Kitaev interactions are identified. The full phase diagram of the KJ model is determined using exact diagonalization and density matrix renormalization group methods, which shows a striking similarity to the KJ model on a two-dimensional honeycomb lattice. |
Monday, March 4, 2019 10:48AM - 11:00AM |
A37.00011: Ground-state phase diagram of the Kitaev-Heisenberg model on a kagome lattice Katsuhiro Morita, Masanori Kishimoto, Takami Tohyama The Kitaev-Heisenberg model on the honeycomb lattice has been studied for the purpose of finding exotic states such as quantum spin liquid and topological orders. On the kagome lattice, in spite of a spin-liquid ground state in the Heisenberg model, the stability of the spin-liquid state has hardly been studied in the presence of the Kitaev interaction. Therefore, we investigate the ground state of the classical and quantum spin systems of the kagome Kitaev-Heisenberg model. In the classical system, we obtain an exact phase diagram that has an eight-fold degenerated canted ferromagnetic phase and a subextensive degenerated Kitaev antiferromagnetic phase. In the quantum system, using the Lanczos-type exact diagnalization and cluster mean-field methods, we obtain two quantum spin-liquid phases, an eight-fold degenerated canted ferromagnetic phase similar to the classical spin system, and an eight-fold degenerated q=0, 120o ordered phase induced by quantum fluctuation. |
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