Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P37: Honeycomb Lattice and Other LowD ModelsFocus

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Sponsoring Units: GMAG DCMP DMP Chair: Matthias Gohlke, MaxPlanckInstitut fur Physik komplexer System Room: BCEC 206A 
Wednesday, March 6, 2019 2:30PM  3:06PM 
P37.00001: Quantum Spin Liquid phases in extended Kitaev models on the Honeycomb Lattice Invited Speaker: ZhengXin Liu Kitaev materials have attracted great attention thanks to their potential for realizing the Kitaev model, an exactly solvable spin model that hosts topological quantum spin liquids. However, most Kitaev materials undergo phase transition into a magnetically ordered phase at low temperatures, indicating that nonKitaev interactions are nonneglectible. Recent experiments on the Kitaev material αRuCl_{3} showed that, under very low temperature an intermediate inplane magnetic field can suppress the static zigzag magnetic order and induce a liquidlike disordered phase. The nature of the fieldinduced disordered phase was not fully understood. Motivated by this issue, we studied the KΓ model (K =6.8 meV and Γ= 9.5meV) which was the minimal model prosed to describe the lowenergy physics of αRuCl_{3}. From variational Monte Carlo calculations, we found that inplane magnetic field can indeed cause a phase transition from a zigzag ordered phase into a gapless U(1) Dirac spin liquid phase [1]. Our results semiquatitatively explain the observed temperature dependence of spinlattice relaxation rate 1/T_{1}~T^{3 }in a recent nuclear magnetic resonance experiment [2]. It was also shown that an outofplane magnetic field can induce a KalmeyerLaughlintype abelian chiral spin liquid phase, which would show an integerquantized thermal Hall effect. Our theory hopefully captures the low energy physics of αRuCl_{3 }and provides a clue to undertand the experiments in related materials. 
Wednesday, March 6, 2019 3:06PM  3:18PM 
P37.00002: Fieldorientationdependent spin dynamics of the Kitaev honeycomb model David Ronquillo, Adu Vengal, Nandini Trivedi The main question we address is how to probe the fractionalized excitations of a quantum spinliquid (QSL), for example, in the Kitaev honeycomb model. From analyzing the energy spectrum and entanglement entropy, for antiferromagnetic couplings and a field along either [111], or [110], we find a new gapless QSL phase, sandwiched between the nonAbelian Kitaev QSL and polarized phases. Rotating the field towards [001] destroys this intermediate QSL phase and results in a considerable reduction in the number of frequency modes. In certain parameter regimes, we observe a beating pattern in the local dynamical correlations, possibly observable in pumpprobe experiments. Finally, we explore the field strength and orientation dependence of the longitudinal and transverse thermal conductivities of this model as a function of temperature. 
Wednesday, March 6, 2019 3:18PM  3:30PM 
P37.00003: Chiral spin liquid near the ferromagnetic Kitaev regime under a magnetic field Jacob Gordon, Andrei Catuneanu, Erik Sorensen, HaeYoung Kee The Kitaev model is a rare example of an exactly solvable model which exhibits a spin liquid ground state, and hosts nonAbelian anyon excitations. Recent research has focused on material realization of Kitaev physics, with αRuCl_{3} emerging as a leading candidate. Compelling evidence for a chiral spin liquid (CSL) is a halfquantized thermal Hall conductivity in αRuCl_{3}, a signature of Majorana edge currents. However, it remains a nontrivial task to explain the existence of a CSL in αRuCl_{3} from a microscopic model, due to dominant ferromagnetic (FM) Kitaev interactions. This is because the FM Kitaev phase almost immediately transitions to the polarized phase in an applied field, with no intervening phase. Here we present a microscopic theory describing the existence of a CSL near the FM Kitaev regime under a magnetic field. Further implications related to the quantized thermal Hall conductivity are also discussed. 
Wednesday, March 6, 2019 3:30PM  3:42PM 
P37.00004: Classical Kitaev model in a magnetic field Jeffrey G. Rau, Paul A. McClarty, Karlo Penc, Roderich Moessner We study the classical version of Kitaev's honeycomb model in the presence of a magnetic field. For an antiferromagnetic Kitaev coupling a classical spin liquid phase persists over a large window of field strength, independent of field direction. We characterize this phase using analytic arguments, a coarsegrained theory and via Monte Carlo simulations, finding the Coulomb correlations present at zerofield are immediately destroyed when the field is applied. We further probe the nature of this phase via the introduction of vacancies. Over a wide field range we find removing a site leaves the magnetization unchanged, the liquid exactly compensating the missing spin. Finally, we speculate on implications for the quantum model in the semiclassical limit. 
Wednesday, March 6, 2019 3:42PM  3:54PM 
P37.00005: Plaquette order in classical spin liquid stabilized by strong offdiagonal exchange Zhijie Fan, Preetha Saha, Depei Zhang, GiaWei Chern We report a new classical spin liquid in which the collective flux degrees of freedom break the translation symmetry of the honeycomb lattice. This exotic phase exists in frustrated spinorbit magnets where a dominant offdiagonal exchange, the socalled Γ term, results in a macroscopic groundstate degeneracy at the classical level [1]. We demonstrate that the system undergoes a phase transition driven by thermal orderbydisorder at a critical temperature T_{c} ≈ 0.04 Γ. Interestingly, while the cubic symmetry is broken at T < T_{c}, spins in the low temperature phase remain disordered. We show that this phase transition actually corresponds to plaquette ordering of hexagonal fluxes. By introducing a proper order parameter to describe this translational symmetry breaking, we performed extensive Monte Carlo simulations and finitesize analysis to investigate the nature of the plaquetteordering transition. We also study the dynamical behavior of fluxes and the influence of other types of interactions on the phase transition.[1] I. Rousochatzakis and N. B. Perkins Phys. Rev. Lett. 118, 147204 (2017). 
Wednesday, March 6, 2019 3:54PM  4:06PM 
P37.00006: Designing S = 1 Kitaev materials Andrei Catuneanu, Panagiotis Peter Stavropoulos, Darren Pereira, HaeYoung Kee As the spin S = 1/2 Kitaev model is gaining increasing attention, there have been theoretical efforts to understand if S = 1/2 Kitaev features appear in generalized Kitaev models with higher spins. In particular, numerical studies on the S = 1 Kitaev model show interesting results, but there is no microscopic understanding on how to generate such a bonddependent S = 1 interaction in solid state materials. Here we present a microscopic mechanism and necessary ingredients to design the S = 1 Kitaev interaction. Candidate materials are also discussed. 
Wednesday, March 6, 2019 4:06PM  4:18PM 
P37.00007: Dynamical and finite temperature properties of Kitaev magnet betaLi2IrO3 in magnetic field Mengqun LI, Ioannis Rousochatzakis, Natalia Perkins We present theoretical study of the fieldinduced magnetic phases in the threedimensional, hyperhoneycomb Kitaev compound betaLi2IrO3. We show that a relatively weak magnetic field along the crystallographic baxis drives the system from its incommensurate counterrotating order to a correlated paramagnet, with a significant uniform ‘zigzag’ component superimposing the magnetization along the field. We compute the magnon excitation spectra, the dynamical spin structure factors and their polarization dependence and argue that our results provide additional distinctive fingerprint that can be checked experimentally. Finally, using extensive Monte Carlo simulations, we study the evolution of the magnetic orders with temperature and provide the finite temperature phase diagram of fieldinduced magnetic phases. 
Wednesday, March 6, 2019 4:18PM  4:30PM 
P37.00008: Using light to tune magnetism on the honeycomb lattice Victor Quito, Rebecca Flint The search for spin liquid phases in condensed matter systems has generated a lot of interest in recent years. In practice, however, such phases are usually restricted to small regions of phase diagrams, which makes them challenging to access in experiments. Concerning this issue, circularly polarized Floquet potentials have been shown to generate chiral fields on the kagome lattice, making it possible to tune between Z2 and chiral spin liquids [1]. Given the potential deconfined criticality and chiral spin liquid phases on honeycomb lattices, here we address the effects of different Floquet potentials in these lattices. We discuss, in particular, how periodic optical drives can be used to manipulate different spin exchange couplings. We also comment on how our results can be relevant to experiments. 
Wednesday, March 6, 2019 4:30PM  4:42PM 
P37.00009: Classification of spin liquids on the stuffed honeycomb lattice Jyotisman Sahoo, Dmitrii Kochkov, Bryan Clark, Rebecca Flint We introduce the stuffed honeycomb lattice (a honeycomb lattice coupled to its dual  a triangular lattice) that interpolates between the triangular and the honeycomb lattices. We consider S = 1/2 Heisenberg spins. Our classical phase diagram reveals a multicritical point on the triangular lattice axis, with two new neighboring noncollinear phases appearing only off axis. Our quantum phase diagram found via exact diagonalization hosts a large spin liquid (SL) region that eats up most of the phase space of the new classical phases around the multicritical point. We present a projective symmetry group analysis of all possible symmetric SLs on the stuffed honeycomb lattice and attempt to probe the possible nature (gapless, nematic, etc) to compare to the SL region found in exact diagonalization. Among these SLs, we focus on characterizing the competitive ones found in a variational Monte Carlo analysis. 
Wednesday, March 6, 2019 4:42PM  4:54PM 
P37.00010: Fieldinduced Spin Liquidlike State in a Magnetic Honeycomb Lattice Ruidan Zhong, Robert Cava Quantum fluctuations in magnetic lattices can yield a quantum spin liquid (QSL) state, where no longrange order appears even at zero temperature. The variety of mechanisms that can generate the spin liquid state and the more exotic QSL state remain unclear, however. Here, we report a new magnetic honeycomb system, BaCo_{2}(P_{1x}V_{x})_{2}O_{8}, in which the spin correlations can be tuned by the disorder, leading to different magnetic behaviors. At low x, the material has a spin glass ground state that appears to be due to coexisting and competing correlations. We have found that an external magnetic field can introduce spin liquidlike behavior for some members of the solid solution, testified by the magnetic and thermodynamic experiments. Our results suggest that structural geometry, chemical disorder and external field may help enhance quantum fluctuations in magnetic honeycomb materials. 
Wednesday, March 6, 2019 4:54PM  5:06PM 
P37.00011: Ripple state in the frustrated honeycomblattice antiferromagnet Tokuro Shimokawa, Hikaru Kawamura Rich nontrivial magnetic structures in multipleq states have attracted much attention these days. One of the most celebrated example might be a skyrmionlattice state known as a tripleq state with forming periodic vortexcrystal structure. We have found a new type of multipleq state, a "ripple state" in the J_{1}J_{2} classical honeycomblattice Heisenberg antiferromagnet by means of extensive Monte Carlo simulations. This honeycomb model has been known to have an infinite ringlike degeneracy in the ground state. In the ripple state, surprisingly, orderbydisorder mechnism does not work and all wavevectors on the degenerate ring equally contribute to its order. The realspace spin texture of the ripple state does not form a crystal in spite of the breaking of the translational symmetry and seems to be like a "water ripple" observed when we throw a stone on the surface of water. We will talk about the detail of the intringuing properties of the ripple state and discuss the possible realization in the honeycomblattice spinliquid material, Bi_{3}Mn_{4}O_{12}(NO_{3}). 
Wednesday, March 6, 2019 5:06PM  5:18PM 
P37.00012: AKLTlike valence bond solid state in the frustrated ferromagnetic J_{1}J_{2} chain Cliò Efthimia Agrapidis, StefanLüdwig Drechsler, Jeroen Van den Brink, S. Nishimoto

Wednesday, March 6, 2019 5:18PM  5:30PM 
P37.00013: Critical properties of sixstate clock model on randomly frustrated 2D lattices Tasrief Surungan We study the antiferromagnetic sixstate clock model 
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