Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J47: Kitaev Magnetism: TheoryFocus
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Sponsoring Units: GMAG DMP Chair: Stephen Winter, Goethe University Frankfurt Room: 710/712 |
Tuesday, March 3, 2020 2:30PM - 2:42PM |
J47.00001: Understanding the Magnetic-Field Anisotropy of Kitaev Materials Ahmed Rayyan, Jacob Gordon, Hae-Young Kee The Kitaev spin liquid remains the most theoretically well-understood quantum spin liquid due to the exact solvability of the Kitaev model. However, other interactions such as the off-diagonal spin interactions render the model non-integrable, but give rise to the magnetic order seen at low temperatures in candidate materials. Recently it was shown that when a magnetic field is applied along a certain direction, the magnetic order melts into an intermediate-field phase before the spins are fully polarized, A thorough understanding of the interplay between field and spin exchange anisotropy is required to understand field-induced phases. To this end, we present the classical and quantum phase diagrams of the extended anisotropic Kitaev model under different magnetic field directions. |
Tuesday, March 3, 2020 2:42PM - 2:54PM |
J47.00002: Majorana-magnon crossover by a magnetic field in the Kitaev model Yukitoshi Motome, Junki Yoshitake, Joji Nasu, Yasuyuki Kato Kitaev quantum spin liquids host Majorana fermions via the fractionalization of spins. In a magnetic field, the Majorana fermions were predicted to comprise a topological state with anionic excitations, which has attracted great attention by the recent discovery of the half-quantized thermal Hall conductivity. Nevertheless, a reliable theory remains elusive for the field effect, especially at finite temperature. Here we present unbiased large-scale numerical results for the Kitaev model in a wide range of magnetic field and temperature, obtained by continuous-time quantum Monte Carlo simulations. We find that the unconventional paramagnetic region showing fractional spin dynamics extends at finite temperature, far beyond the field range where the topological state is expected at zero temperature. Our results show the confinement-deconfinement behavior between the fractional Majorana excitations and the conventional magnons. |
Tuesday, March 3, 2020 2:54PM - 3:06PM |
J47.00003: Spin-one Kitaev model, same but different? Ilia Khait, Hae-Young Kee, Yong-Baek Kim We study various properties of the spin-one Kitaev model on honeycomb lattices consisting of two and three-leg ladder geometries using density matrix renormalization group. We discuss similarities to the spin-half model, and outline differences. Our results suggest that the spin-one model is a bona fide spin liquid candidate. |
Tuesday, March 3, 2020 3:06PM - 3:18PM |
J47.00004: Vacancy-induced Low-energy States in the Kitaev Model Wen-Han Kao, Johannes Knolle, Roderich Moessner, Natalia Perkins Since 2006, the Kitaev honeycomb model has attracted significant attention due to the exactly solvable spin-liquid ground state with fractionalized Majorana excitations [1] and the possible materialization in magnetic Mott insulators with strong spin-orbit couplings [2]. Recently, the 5d-electron compound H3LiIr2O6 has shown to be a strong candidate of Kitaev physics considering the absence of long-range ordered magnetic state [3]. In this work, we demonstrate that a finite density of random vacancies gives rise to a remarkable pile up of low-energy states and possibly explains the experimental findings in H3LiIr2O6. We study both the free-flux and the vacancy-induced bound-flux background and their responses to additional time-reversal symmetry-breaking term, which imitates the magnetic field in real experiments. |
Tuesday, March 3, 2020 3:18PM - 3:30PM |
J47.00005: Field induced phases of the Kitaev-Γ ladder Erik Sorensen, Andrei Catuneanu, Jacob Gordon, Hae-Young Kee The Kitaev spin model on honeycomb lattice has attracted significant attention since the emergence of α-RuCl3 as a promising Kitaev spin liquid candidate in the presence of a magnetic field. While the mechanism of such a field-induced Kitaev spin liquid is not yet fully understood, theoretical studies have shown that the bond-dependent Γ and Kitaev interactions are equally significant in α-RuCl3 leading to a minimal spin-½ Kitaev-Γ (KG) model. In the pure antiferromagnetic Kitaev limit, previous numerical studies have shown gapless states for a range of intermediate field strengths, leading to the suggestion of a U(1) spin liquid phase. However, a possibility of incommensurate magnetic orderings cannot be excluded. Employing large-scale numerical techniques, we study the KG model in a two-leg ladder system in the presence of a magnetic field for the entire phase space of the KG model, finding both disordered and incommensurate ordered phases near the antiferromagnetic Kitaev region. We discuss the models limitations and relation to the two-dimensional honeycomb lattice. |
Tuesday, March 3, 2020 3:30PM - 3:42PM |
J47.00006: Field-Driven Phenomena in 2-d and 3-d Kitaev Magnets Ciaran Hickey, Simon Trebst, Matthias Gohlke, Christoph Berke Kitaev's honeycomb model is an exactly solvable spin model that realises a quantum spin liquid ground state, with fractionalised excitations in the form of Majorana fermions and plaquette flux excitations. Recent studies have shown that applying an external magnetic field can give rise to a rich set of field-driven phenomena, including the appearance of a gapless U(1) spin liquid. However, the Kitaev model is not unique to the honeycomb lattice, the model can in fact be defined, and exactly solved, on a range of tri-coordinated lattices in two and three dimensions. This naturally provides an enormous playground within which to study field-driven phenomena in quantum spin liquids. We will discuss a number of examples and construct a generic phase diagram for the Kitaev model in the presence of a magnetic field. |
Tuesday, March 3, 2020 3:42PM - 3:54PM |
J47.00007: Magnetic Field Induced Competing Phases in Spin-Orbital Entangled Kitaev Magnets Li Ern Chern, Ryui Kaneko, Hyun-Yong Lee, Yong-Baek Kim There has been a great interest in magnetic field induced quantum spin liquids in Kitaev magnets after the discovery of neutron scattering continuum and half quantized thermal Hall conductivity in the material $\alpha$-RuCl$_3$. In this work, we provide a semiclassical analysis of the relevant theoretical models, which enable us to treat large system sizes approximating the thermodynamic limit. We find a series of competing magnetic orders with fairly large unit cells at intermediate magnetic fields, which are mostly missed by previous studies. We show that quantum fluctuations are typically strong in these large unit cell orders, while the spin wave dispersion resembles a scattering continuum. The huge quantity of magnon bands with finite Chern numbers also gives rise to an unusually large thermal Hall conductivity. Given the highly frustrated nature of the spin model, the large unit cell orders are likely to melt into the putative spin liquid in the quantum limit. Our work provides an important basis for a thorough investigation of emergent spin liquids and competing phases in Kitaev magnets. [arXiv:1905.11408] |
Tuesday, March 3, 2020 3:54PM - 4:06PM |
J47.00008: Numerical Studies of the Kitaev-Gamma Model Under a Magnetic Field Jacob Gordon, Andrei Catuneanu, Hae-Young Kee Recently, there has been excitement generated around α-RuCl3 as a candidate for the material realization of the Kitaev spin liquid (KSL). Beyond the dominant ferromagnetic (FM) Kitaev interaction, subleading spin interactions are required to explain the zig-zag (ZZ) magnetic ordering and behaviour of α-RuCl3 under a magnetic field. On the basis of exact diagonalization (ED) and DMRG, an antiferromagnetic (AFM) Gamma interaction was found to be essential for stabilizing the KSL under tilted magnetic fields. A subsequent classical study of the Kitaev-Gamma model found a multitude of large unit cell magnetic orders due to the competition between Gamma and the applied field. Furthermore, an infinite tensor product state (iTPS) study found that these classical orders are melted by quantum fluctuations, giving way to two nematic paramagnetic states. The topological nature of these nematic phases and their relation to the KSL remain unknown. Here we present results obtained with ED to address these open questions. |
Tuesday, March 3, 2020 4:06PM - 4:42PM |
J47.00009: Vison crystals in an extended Kitaev model on the Honeycomb latttice Invited Speaker: Cristian Batista
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Tuesday, March 3, 2020 4:42PM - 4:54PM |
J47.00010: Partitioning the phase diagram of pyrochlore and Kitaev magnets using graph theory Ke Liu, Jonas Greitemann, Ludovic DC Jaubert, Han Yan, Nicholas Shannon, Lode Pollet Highly frustrated magnets host rich exotic states of matter such as spin liquids and hidden orders. Those phases can occur in various forms and are notoriously difficult to identify. In this talk, I will show that the combination of a kernel method and graph partitioning theory provides an efficient framework to unravel the complex phase diagram of frustrated magnets. It delimits regimes of both classical spin liquids and broken symmetry phases, including hidden orders, and provides the analytical order parameters and/or characteristic local constraints. The method is demonstrated by examples of pyrochlore and Kitaev magnets but applies to general (semi-)classical spin systems. |
Tuesday, March 3, 2020 4:54PM - 5:06PM |
J47.00011: Quantum Spin Liquid and Proximate Magnetic Orders in Magnets with Spin-Orbit Coupling Animesh Nanda, Kusum Dhochak, Subhro Bhattacharjee Quantum phase transitions out of magnetic orders in quantum spin liquid (QSL) phases have gained much recent attention in the context of several spin-orbit coupled magnets such as α-RuCl3, Yb2Ti2O7 etc. In this talk, I shall report our theoretical calculations about the nature of such unconventional phase transition in a class of experimentally relevant Hamiltonians in the honeycomb magnets. In particular, we shall show how such deconfined quantum phase transitions are naturally captured in terms of the condensation of the fractionalised excitations of the QSL. In addition, we shall show how to think about such transitions in terms of the domain walls of the magnetically ordered phases. |
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