Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E39: Spin Ice II & Kitaev Systems IIIFocus Live
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Sponsoring Units: GMAG DMP Chair: Claudio Castelnovo, Univ of Cambridge |
Tuesday, March 16, 2021 8:00AM - 8:12AM Live |
E39.00001: Distinguishing dipolar and octupolar quantum spin ices Adarsh S Patri, Masashi Hosoi, Yong-Baek Kim Quantum spin liquids (QSLs) and Multipolar ordered states (MPOs) both share the property of being notoriously difficult to detect with conventional probes. Recently, the existence of two distinct quantum spin liquids, dipolar QSL (d-QSL) and octupolar QSL (o-QSL) was proposed in a class of pyrochlore materials. However, how to distinguish them has been an open question due to the difficulty in detecting the multipolar nature of such quantum spin liquids. Motivated by this situation, we investigate the possibility of distinguishing them by using a lattice-based technique. In this talk, we theoretically propose that a magnetostriction measurement can be used as a powerful tool to access the novel properties of multipolar-based quantum spin liquids. |
Tuesday, March 16, 2021 8:12AM - 8:24AM Live |
E39.00002: Hidden phases born of a quantum spin liquid: Application to pyrochlore spin ice Hyeok-Jun Yang, Nicholas Shannon, SungBin Lee Quantum spin liquids (QSL) have been focused as promising ground states of the frustrated magnets supporting fractionalized quasi-particles with the emergent gauge structures. Plenty of such deconfined phases turn out to be quite stable against weak perturbations, whereas the strong coupling drives the system to be conventionally ordered. However, this standard instruction of the lattice gauge theory leaves an open question on the intermediate regime between deconfined and fully-confined limits. Here, we formulate the effective parton interactions to explore the hidden phases beyond the perturbative approach. We show that the intermediate coupling generically arouses novel phases whose gauge structure is partially lifted before the full confinement. By reformulating the pyrochlore spin model, abundant daughter phases including Z2 QSLs and a spinon supersolid descended from U(1) QSL are proposed with experimental signatures. We discuss the relevant numerical results supporting our formalism as a platform for searching new exotic phases of matter in frustrated magnets. |
Tuesday, March 16, 2021 8:24AM - 8:36AM Live |
E39.00003: The Emergent Fine Structure Constant of Quantum Spin Ice Is Large Salvatore Pace, Siddhardh C Morampudi, Roderich Moessner, Christopher Laumann Condensed matter systems act as mini-universes with emergent low-energy properties drastically different from those of the standard model. A case in point is the emergent quantum electrodynamics (QED) in the fractionalized topological magnet known as quantum spin ice, whose magnetic monopoles set it apart from the familiar QED of the world we live in. Here, we show that the two greatly differ in their fine-structure constant α, which parametrizes how strongly matter couples to light: αQSI is more than an order of magnitude greater than αQED≈1/137. Furthermore, αQSI, the emergent speed of light, and all other parameters of the emergent QED, are tunable by engineering the microscopic Hamiltonian. We find that αQSI can be tuned all the way from zero up to what is believed to be the strongest possible coupling beyond which QED confines. The large αQSI implies that experiments probing candidate condensed-matter realizations of quantum spin ice should expect to observe phenomena arising due to strong interactions such as well-defined Coulomb bound states, Sommerfeld enhancement of particle pair creation, and copious emergent Cerenkov radiation. At finite temperature, the system further provides a platform for studying a strongly coupled electro-magnetic plasma. |
Tuesday, March 16, 2021 8:36AM - 8:48AM Live |
E39.00004: Persistent homology as an order parameter for classical spins Bart Olsthoorn, Johan Hellsvik, Alexander Balatsky Classical spin models can feature rich phase diagrams that are difficult to characterize without knowing the order parameter. Phases can have strong correlations while lacking magnetic ordering, such as e.g. nematic ordering which breaks spin rotational symmetry. We show that persistent homology – a relatively new field in applied mathematics – can be used as a universal framework to construct a phase diagram [1]. Finally, we demonstrate this new approach using the XXZ model on the pyrochlore lattice and automatically identify all six phases, including hidden phases such as the spin-ice phase. |
Tuesday, March 16, 2021 8:48AM - 9:00AM Live |
E39.00005: U(1) and Z2 spin liquids on the pyrochlore lattice Chunxiao Liu, Gábor Halász, Leon Balents The geometrically frustrated 3D pyrochlore lattice has been long predicted to host a quantum spin liquid. To this date, most proposals for pyrochlore materials have been a U(1) quantum spin liquid whose only low energy excitations are emergent photons of Maxwell type. In this work we explore the possibility of finding spin liquids whose low energy theories go beyond this standard one. We give a complete classification of symmetric U(1) and Z2 spin liquids on pyrochlore using the projective symmetry group method for the fermionic spinons. We find 22 and 28 classes for the U(1) and the Z2 types without considering time reversal, while upon adding time reversal the numbers of classes become 16 and 48, respectively. For each class the most general symmetry-allowed spinon mean-field Hamiltonian is given. We find that several U(1) classes possess an unusual gapless multi-nodal line structure in the spinon bands, which is protected by the (projective) three-fold rotation and screw symmetries of the pyrochlore space group. Via a toy model, we consider the effect of gauge fluctuations for such a nodal structure and study the various thermodynamic properties of this system. |
Tuesday, March 16, 2021 9:00AM - 9:12AM Live |
E39.00006: Importance of dynamic lattice effects for crystal field excitations in quantum spin ice candidate Pr2Zr2O7 Yuanyuan Xu, Huiyuan Man, Nan Tang, Santu Baidya, Satoru Nakatsuji, David Vanderbilt, Natalia Drichko Pr2Zr2O7 is a quantum spin ice candidate, where a splitting of the Pr3+ non-Kramers ground state doublet was suggested as an origin of the transverse field component leading to the exotic physics in this material [1]. We performed the low temperature Raman scattering experiments on Pr2Zr2O7 single crystals to probe the crystal electric field excitations and phonons. We directly observed a splitting of the excited state doublet at around 55 meV which originates from vibronic coupling of the Eg doublet with a phonon. We deduct a 1 meV splitting of the ground state Eg doublet from the line shape of the excitation to the first excited A1g state. The well-defined splitting of the ground state suggests that static or low frequency dynamic deviation of Pr3+ environment from D3d symmetry causes the splitting. |
Tuesday, March 16, 2021 9:12AM - 9:48AM Live |
E39.00007: Realization of the kagome spin ice state in frustrated intermetallic HoAgGe Invited Speaker: Kan Zhao Frustration in spin systems can result in the formation of exotic phases of matter. Spin ices are exotic phases of matter characterized by frustrated spins obeying local “ice rules”, in analogy with the electric dipoles in water ice (1). In two dimensions, one can similarly define ice rules for in-plane Ising-like spins arranged on a kagome lattice (2-3). These ice rules require each triangle plaquette to have a single monopole, and can lead to various unique orders and excitations (2-3). Using experimental and theoretical approaches including magnetometry, thermodynamic measurements, neutron scattering and Monte Carlo simulations, we establish HoAgGe as a crystalline (i.e. non-artificial) system that realizes the kagome spin ice state. The system features a variety of partially and fully ordered states and a sequence of field-induced phases at low temperatures, all consistent with the kagome ice rule (4). |
Tuesday, March 16, 2021 9:48AM - 10:00AM Live |
E39.00008: Observation of magnetic ordering in Kitaev material Ag3LiIr2O6 in the absence of structural disorder Faranak Bahrami, Eric Kenney, Chennan Wang, Adam Berlie, Oleg I. Lebedev, Michael John Graf, Fazel Tafti The search for an ideal Kitaev material without long-range magnetic order has led to development of a new family of Kitaev magnets via topotactic cation exchange reaction. However, the structural disorder that can be produced by this method may suppress the magnetic ordering. In this talk, we present a comparative study between clean and disordered samples of Ag3LiIr2O6 to highlight the effects of structural disorder on the magnetic behavior of the material. In the disordered sample, the absence of a susceptibility peak and a weakly depolarizing μSR signal suggest proximity to the Kitaev spin liquid phase. In contrast, the clean sample shows a peak in both susceptibility and heat capacity measurements with a clear oscillation in the μSR depolarization which rules out a spin liquid ground state. Our results emphasize the importance of sample quality and encourage further studies into the effects of structural disorder on this family of compounds. |
Tuesday, March 16, 2021 10:00AM - 10:12AM Live |
E39.00009: Symmetry Analysis of Tensors for the Honeycomb Lattice of Edge-Sharing Octahedra Franz Utermohlen, Nandini Trivedi We obtain the most general form of rank-2 and rank-3 tensors allowed by the symmetries of a honeycomb lattice of edge-sharing octahedra (such as alpha-RuCl3 and CrI3). We highlight some unexpected results, including the equality of a fully-longitudinal component to a partially-transverse component. Finally, we compare these findings to a recent thermal Hall experiment in alpha-RuCl3 and make predictions for systems with topological bands. |
Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E39.00010: Visualization of Isospin Momentum Texture of Dirac Magnons and Excitons in a Honeycomb Quantum Magnet Miska Elliot, Paul McClarty, Dharmalingam Prabhakaran, Roger D Johnson, Helen Walker, Pascal Manuel, Radu Coldea Band topology in electronic systems is known to have profound consequences on various observable properties in semi-metals and certain insulators. Insights from this field have reached into many areas of physics and in this talk we describe certain universal signatures of band topology in propagating bosonic quasi-particles. We show that the Dirac magnon material CoTiO3 provides an experimental demonstration of a universal winding of the inelastic neutron scattering intensity around linear touching points of magnetic excitations - magnons and spin-orbit excitons - that originates from the isospin texture of the quasiparticle wavefunction in momentum space. https://arxiv.org/abs/2007.04199 |
Tuesday, March 16, 2021 10:24AM - 10:36AM Live |
E39.00011: Understanding the magnetic interactions of the zig-zag honeycomb lattice: Application to RuCl3 Evan Wilson, Jason Haraldsen In this talk, we investigate the effects of variable exchange interactions on the spin dynamics of the zig-zag honeycomb lattice. Using a Holstein-Primakoff expansion of the Heisenberg Hamiltonian with easy-axis anisotropy, we characterize the effects of multiple nearest-neighbor and next-nearest-neighbor interactions with the context of a frustrated and non-frustrated zig-zag magnetic configuration. Furthermore, we compare to the known inelastic neutron scattering data for RuCl3 and we provide insight into the evolution of the spin dynamics. By analyzing the frustrated system with multiple interactions, we are able to demonstrate that a standard Heisenberg model can produce an accurate model of the observed spin-waves. |
Tuesday, March 16, 2021 10:36AM - 10:48AM Live |
E39.00012: Ground-state phase diagram of the S=1/2 Heisenberg-Γ model on a honeycomb lattice. Takafumi Suzuki, Takuto Yamada, Sei-ichiro Suga We investigate the ground-state phase diagram of the S=1/2 Heisenberg-Γ model on a honeycomb lattice by utilizing several numerical methods, such as dimer series expansion, the numerical exact-diagonalization method and the density-matrix-renormalization-group method. In this study, we focus on the effect of the anisotropic interaction; we investigate the ground state from the isolated dimer limit to the spin-chain limit by changing the coupling constants. From the results obtained, we find that in the spin-chain limit, there are three kinds of states, namely the Tomonaga-Luttinger liquid state and two magnetically long-range-ordered states. These three states become two-dimensional long-range ordered states by adding the infinitesimal interchain interaction. Starting from the isolated dimer limit, we find that a triplet dimer phase can survive up to the isotopically interacting case in a large part of parameter region where the Heisenberg and Γ interactions are ferromagnetic and antiferromagnetic, respectively. Otherwise, a phase transition to a magnetically ordered phase occurs before the isotopically interacting model. This indicates that the quantum spin liquid expected in the Γ model is unstable against the anisotropy of the interactions. |
Tuesday, March 16, 2021 10:48AM - 11:00AM Live |
E39.00013: Ground-state phase diagram of the Kitaev-Γ model on a honeycomb lattice Sei-ichiro Suga, Takafumi Suzuki, Takuto Yamada We investigate the ground-state phase diagram of the Kitaev-Γ model on a honeycomb lattice by utilizing series expansions and numerical exact diagonalizations [1]. We focus on the effects of the anisotropic interactions. Starting from the weakly interacting dimers on the specific bond, we strengthen the interdimer interactions up to the isotropically interacting system. Depending on the strengths of the Kitaev and Γ interactions, the dimer state survives up to the isotropically interacting system, where the phase transition occurs, or obeys a phase transition to a magnetically ordered state at an anisotropic interaction. The results are summarized in the phase diagrams. We also show that the Kekulé dimerized state is unstable in the isotropic Kitaev-Γ model. [1] T. Yamada, T. Suzuki, and S. Suga, PRB 102, 024415 (2020). |
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