Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session K07: Spin Liquids and Ices |
Hide Abstracts |
Sponsoring Units: DCMP GMAG Chair: Randy Fishman, Oak Ridge National Laboratory Room: BCEC 109B |
Wednesday, March 6, 2019 8:00AM - 8:12AM |
K07.00001: Discovery of chiral-spin order in purported Kitaev spin-liquids Chandra Varma, Kimberly Modic, Brad Ramshaw, Arkady Shekhter We examine recent magnetic torque measurements in two compounds, $\gamma$-Li$_2$IrO$_3$ and RuCl$_3$, which have been discussed as possible realizations of the Kitaev model. The analysis of the reported discontinuity in torque, as an external magnetic field is rotated across the $c-$axis in both crystals, suggests that they have a translationally-invariant chiral spin-order of the from $<{\bf S}_i. \big({\bf S}_j~ \times~ {\bf S}_k\big)> \ne 0$ in the ground state and persisting over a very wide range of magnetic field and temperature. An extra-ordinary $|B|B^2$ dependence of the torque for small fields, beside the usual $B^2$ part, is predicted due to the chiral spin-order. Data for small fields is available for $\gamma$-Li$_2$IrO$_3$ and is found to be consistent with the prediction upon further analysis. Other experiments such as inelastic scattering and thermal Hall effect and several questions raised by the discovery of chiral spin-order, including its topological consequences are discussed. |
Wednesday, March 6, 2019 8:12AM - 8:24AM |
K07.00002: Characteristics of the intermediate-field ordered phase of alpha- RuCl3 revealed by magnetic diffraction Arnab Banerjee, Christian Balz, Paige Lampen-Kelley, Jiaqiang Yan, David George Mandrus, Yaohua Liu, Stephen Nagler There has been great interest in alpha-RuCl3 as a material that manifests Kitaev terms in the spin Hamiltonian and a possible field-induced quantum spin liquid (QSL) phase by 8 T [1]. Bulk Measurements show that in the in-plane magnetic field causes a transition to an intermediate ordered phase around 6 Tesla [1, 2], preceding the total suppression of magnetic order around 7.3 T. Here we use time-of-flight neutron diffraction to elucidate the nature of intermediate phase and its magnetic order. Our results provide new insights into the dimensionality of the magnetic order and the effective spin-Hamiltonian of the material. |
Wednesday, March 6, 2019 8:24AM - 8:36AM |
K07.00003: Magnon thermal Hall effect in the candidate Kitaev spin-liquid α-RuCl3 Jonathan Cookmeyer, Joel Moore Motivated by recent experiments measuring the thermal Hall conductivity of α-RuCl3 and using spin-wave theory and model effective Hamiltonians from the literature, the magnon Thermal Hall coefficient in the magnetically ordered phase is computed. Comparing directly with the experiment, no previously proposed model well matches the data. A model is determined which can explain the data demonstrating that the magnon Berry curvature could be responsible. The discrepancy could also be explained by phonons but not by Kitaev-like excitations. |
Wednesday, March 6, 2019 8:36AM - 8:48AM |
K07.00004: Effective dimension, level statistics, and integrability of Sachdev-Ye-Kitaev-like models Eiki Iyoda, Hosho Katsura, Takahiro Sagawa Recently, quantum many-body systems exhibiting fast scrambling (delocalization of quantum information) have attracted much attention. A well-known example is the Sachdev-Ye-Kitaev (SYK) model, describing random all-to-all four-body interactions among fermions. Here, we introduce a variant of the SYK model, which we refer to as the Wishart SYK model [1]. The model includes the original SYK model without quenched disorder as a special case. |
Wednesday, March 6, 2019 8:48AM - 9:00AM |
K07.00005: A candidate Theory for the "Strange Metal" phase based on the Sachdev-Ye-Kitaev physics Xiaochuan Wu, Xiao Chen, Chao-Ming Jian, Yizhuang You, Cenke Xu We propose a lattice model for strongly interacting electrons with the potential to explain the main phenomenology of the strange metal phase in the cuprate high-temperature superconductors. Our model is motivated by the recently developed “tetrahedron” rank-3 tensor model that mimics much of the physics of the better-known Sachdev-Ye-Kitaev (SYK) model. Our electron model has the following advantageous properties: (1) it needs only one orbital per site on the square lattice. (2) It does not require any quenched random interaction. (3) It has local interactions and respects all the symmetries of the system. (4) The soluble limit of this model has a longitudinal dc resistivity that scales linearly with temperature within a finite temperature window. (5) Again, the soluble limit of this model has a fermion pairing instability in the infrared, which can lead to either superconductivity or a “pseudogap” phase. The linear-T longitudinal resistivity and the pairing instability originate from the generic scaling feature of the SYK model and the tetrahedron tensor model. |
Wednesday, March 6, 2019 9:00AM - 9:12AM |
K07.00006: Charge transport in graphene-based mesoscopic realizations of Sachdev-Ye-Kitaev models Oguzhan Can, Emilian Nica, Marcel Franz We address transport properties of a mesoscopic realization of the Sachdev-Ye-Kitaev (SYK) model which is an exactly solvable system of interacting spinless fermions connected to the black hole physics through the holographic principle. Starting with a recent proposal for simulating the SYK model in a graphene flake in an external magnetic field and extending it by considering leads attached to it, we model a realistic transport experiment and calculate directly measurable quantities featuring non-Fermi liquid signatures of the SYK physics. We show that the graphene flake realization is robust in the presence of leads and that measuring the tunneling current across the leads one can experimentally observe a non-Fermi liquid - Fermi liquid transition by tuning the external magnetic field threading the flake. After establishing the transport signatures of the SYK model near equilibrium using linear response framework, we then derive a formula to extend our results for tunneling current using Keldysh formalism to explore the effects of finite bias voltage across the leads, going beyond equilibrium. |
Wednesday, March 6, 2019 9:12AM - 9:24AM |
K07.00007: Characterization of quantum many-body chaos with quantum Lyapunov exponents and by two-point correlations: application to a generalized Sachdev-Ye-Kitaev model Hrant Gharibyan, Masanori Hanada, Brian Swingle, Masaki Tezuka We propose two quantities for characterization of quantum many-body chaos. Firstly, we define a simple quantum generalization of the spectrum of finite-time classical Lyapunov exponents. [1] We study its statistical features for the SYK model and find random matrix behavior, which is lost when the model is deformed away from chaos towards integrability [2] by a random two-fermion term. Secondly, we propose that two-point correlation functions can also characterize quantum many-body chaos, with numerical evidences for the SYK model as well as for the XXZ spin chain with random field, and discuss the plausibility of laboratory experiments. |
Wednesday, March 6, 2019 9:24AM - 9:36AM |
K07.00008: Chiral spin liquid phase of the triangular lattice Hubbard model Aaron Szasz, Johannes Motruk, Michael Zaletel, Joel Moore
|
Wednesday, March 6, 2019 9:36AM - 9:48AM |
K07.00009: Monopoles in Dirac spin liquids I: from spinon band topology to monopole quantum numbers Xueyang Song, Chong Wang, Yin-Chen He, Ashvin Vishwanath We explore a low-energy theory for 2D quantum magnets, the Dirac spin liquid (DSL), a version of Quantum Electrodynamics ( QED$_3$) with four flavors of Dirac fermions coupled to photons. We study the spatial/time-reversal symmetry properties of the magnetic monopoles, an important class of excitations that drive confinement. We show that the underlying band topology of spinon insulators, e.g., quantum spin hall phase/wannier insulator protected by rotation provides crucial information on the tricky Berry phase of monopole (under time-reversal / rotations, respectively). We also prove the existence of a trivial monopole on bipartite lattices by invoking its ascension to a QCD with SU(2) gauge structure. |
Wednesday, March 6, 2019 9:48AM - 10:00AM |
K07.00010: Monopoles in Dirac spin liquids II: towards a unifying description of 2D quantum magnetism Chong Wang, Xueyang Song, Yin-Chen He, Ashvin Vishwanath The understanding of monopole quantum numbers in Dirac spin liquids provides a unified description of 2D quantum magnetism. In particular, it allows us to naturally account for various orders on both bipartite lattices such as the square and honeycomb lattice as well as the non-bipartite triangular and Kagome lattices. A dichotomy in behavior between the bipartite and non bipartite lattices is traced to the difference in monopole symmetry properties on these two lattices. We characterize universal signatures of the Dirac spin liquid state, including those that result from monopole excitations, which serve as a guide to numerics and to experiments on existing materials. Even when unstable, the Dirac spin liquid unifies multiple seemingly unrelated ordered states, which could help organize the plethora of phases observed in strongly correlated two dimensional materials. |
Wednesday, March 6, 2019 10:00AM - 10:12AM |
K07.00011: Interplay of uniform U (1) quantum spin liquid and magnetic phases in rare earth pyrochlore magnets: a fermionic parton approach Sambuddha Sanyal, Kusum Dhochak, Subhro Bhattacharjee We study the uniform time reversal invariant quantum spin liquid (QSL) with low energy fermionic quasi-particles for rare earth pyrochlore magnets and explore its magnetic instability employing an augmented fermionic parton mean field theory approach. Self consistent calculations stabilise an uniform QSL with both gapped and gapless parton excitations as well as fractionalised magnetically ordered phases in an experimentally relevant part of the phase diagram near the classical phase boundaries of the magnetically ordered phases. The gapped QSL has a band-structure with a non-zero topological invariant. The fractionalised magnetic ordered phases bears signature of both QSL through fermionic excitations as well as magnetic order. Thus this provides a possible way to understand the unconventional diffuse neutron scattering in rare-earth pyrochlores such as Yb Ti O , Er Sn O and Er Pt O at low/zero external magnetic fields. We calculate the dynamic spin structure factor to understand the nature of the diffuse two-particle continuum. |
Wednesday, March 6, 2019 10:12AM - 10:24AM |
K07.00012: Microscopic model for Tb-based pyrochlore magnets Wen Jin, Daniel Wong, Michel J P Gingras There have been extensive experimental investigations of the magnetic structures and excitations of Tb-based pyrochlores, Tb2B2O7 (B=Ti, Sn, Ge). Tb2Ti2O7 is a candidate for quantum spin ice, while Tb2Sn2O7 and Tb2Ge2O7 have long-range ordered spin ice state coexistent with strong spin fluctuations. However, a microscopic model of these materials is still lacking. In this talk, I will discuss our efforts to derive a pseudo spin-1/2 model of Tb-based pyrochlores via a projection operator approach. We find the virtual crystal field excitations between the two lower doublets result in significant renormalization of the classical Ising interactions and generate symmetry-allowed three-body interactions that play a crucial role in the selection of ground state. We find the electric quadrupole-quadrupole interactions also give rise significant quantum fluctuations. |
Wednesday, March 6, 2019 10:24AM - 10:36AM |
K07.00013: Magnetic critical dynamics and monopole clustering of pyrochlore spin ice Puhan Zhang, Jing Luo, Gia-Wei Chern Spin-ice materials such as Ho2Ti2O7 and Dy2Ti2O7 are a class of geometrically frustrated ferromagnets that retain an extensive residual entropy even at very low temperatures. Importantly, the elementary dipole excitations fractionalize into magnetic monopoles in these compounds. Indeed, the field-induced first-order transition in spin-ice compounds can be understood as a monopole liquid-gas transition. Despite extensive studies on magnetic monopole dynamics at low magnetic field, the kinetics of the liquid-gas transition and the particular role played by monopoles have not been thoroughly investigated. Here we present extensive numerical simulations to investigate the structural as well as dynamical properties of monopoles in the vicinity of the field-induced first-order transition. Our results relate the critical magnetic dynamics to the percolation of magnetic monopoles in the monopole gas phase. Interestingly, we show that similar percolating clusters consisting of bound monopole hole pairs also appear in the dense monopole liquid phase. |
Wednesday, March 6, 2019 10:36AM - 10:48AM |
K07.00014: Quantum Anomalous Hall Phase Stabilized via Realistic Interactions on a Kagome Lattice Yafei Ren, Tiansheng Zeng, Wei Zhu, Donna Sheng Spontaneous topological phases driven by interactions have been proposed in various lattice models, which, however, have not been observed in experiments. In this work, we report an experimentally feasible scheme of realizing spontaneous quantum anomalous Hall effect (QAHE) driven by spatially decaying interactions between spinless Fermions on a topologically trivial kagome lattice with a quadratic band touching Fermi point. In the presence of weak first and second nearest-neighbor repulsive interactions (V1 and V2), the presence of QAHE is demonstrated by employing exact diagonalization and density-matrix renormalization group methods. The time-reversal symmetry is broken spontaneously by forming loop currents with long-range correlation. Quantized Hall conductance is obtained by measuring the pumped charge through inserting flux in a cylinder geometry. We find that the topologically nontrivial energy gap can be enhanced remarkably by a moderate V2<V1 via calculating the spectrum and charge excitation gaps. |
Wednesday, March 6, 2019 10:48AM - 11:00AM |
K07.00015: Probing The Spin-Spin Correlator Of Kagome Lattice Heisenberg Antiferromagnets Through Non-linear Optical Harmonic Generation Nicholas Laurita, Alon Ron, Jeong Woo Han, Jongseok Lee, John P Sheckelton, Rebecca W. Smaha, Wei He, Jiajia Wen, Young Sang Lee, Michael Norman, David Hsieh Antiferromagnetically coupled quantum spins on the Kagome lattice are proposed to realize a spin-liquid ground state where short-range spin correlations exist but symmetry breaking is avoided through frustration and quantum fluctuations. The temperature dependence of the short-range spin-spin correlator is important for understanding the underlying spin Hamiltonian of candidate materials but is typically difficult to measure. Here we show that the non-linear optical response embeds the spin-spin correlator in spin-liquid candidates by performing high harmonic generation experiments on Herbertsmithite and Zn-Barlowite. We find the temperature evolution of the spin correlations of these materials to be in very good agreement with the theoretical prediction for the S = 1/2 Heisenberg Kagome antiferromagnet. These results provide a new route to probing the governing spin Hamiltonian of spin-liquid candidates. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700