Bulletin of the American Physical Society
86th Annual Meeting of the APS Southeastern Section
Volume 64, Number 19
Thursday–Saturday, November 7–9, 2019; Wrightsville Beach, North Carolina
Session H02: Frustrated Quantum Magnets |
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Chair: Lin Hao, University of Tennessee Room: Holiday Inn Resort Airlie/Tidewater |
Saturday, November 9, 2019 8:00AM - 8:30AM |
H02.00001: Chemistry Perspectives to Novel Quantum Materials Invited Speaker: Weiwei Xie Design and discovery of new quantum materials will accelerate the development of new technologies in the future. I will report my group research progress in the past year, mainly focusing on the new superconductors and new magnetic topological quantum materials. Superconductors are naturally an ideal platform for quantum information processing (QIP), as they realize electrons to be entangled by forming cooper pairs. My group recently discovered several new superconductors. I will explain our interpretation of this work. More importantly, we are trying to use chemical bonding concept to predict the existence of superconductivity in the materials. \\ Magnetic topological quantum materials (MTQMs) can give rise to forefront electronic properties such as the quantum anomalous Hall effect, axion electrodynamics and Majorana fermions. In our group, we used chemistry electron count rules and structure-property relationship to design new MTQMs. I will describe how to design and prove the material candidate as a new MTQM from both experimental and theoretical aspects and show how topological electronic states and magnetism interplay in the new material. [Preview Abstract] |
Saturday, November 9, 2019 8:30AM - 9:00AM |
H02.00002: Quantum versus Classical Spin Fragmentation In Dipolar Kagome Ice Ho3Mg2Sb3O14 Invited Speaker: Zhiling Dun A promising route to realize entangled magnetic states combines geometrical frustration with quantum-tunneling effects. Spin-ice materials are canonical examples of frustration, and Ising spins in a transverse magnetic field are the simplest many-body model of quantum tunneling. Here, we show that the tripod kagome lattice material Ho${_3}$Mg${_2}$Sb${_3}$O${_{14}}$ unites an ice-like magnetic degeneracy with quantum-tunneling terms generated by an intrinsic splitting of the Ho$^{3+}$ ground-state doublet, which is further coupled to a nuclear spin bath. Using neutron scattering and thermodynamic experiments, we observe a symmetry-breaking transition at $T^{\ast}\approx0.32$ K to a remarkable quantum state with three peculiarities: a dramatic recovery of magnetic entropy associated with the strongly coupled electronic and nuclear degrees of freedom; a fragmentation of the spin into periodic and ice-like components strongly affected by quantum fluctuations; and persistent inelastic magnetic excitation spectrum down to $T\approx0.12$ K. These observations deviate from expectations of classical spin fragmentation physics on a kagome lattice, which can be alternatively understood in a framework of dipolar kagome ice under a homogeneous transverse field. Using various theoretical approaches, including random phase approximation, mean-field approximation, and exact diagonalization, our calculations establish the existence of a highly entangled fragmented state in a region where the transverse field remains a perturbation to the dipole-dipole interactions, which we coin as a quantum spin fragmented state. However, hyperfine interactions play a crucial role in suppressing quantum correlations and dramatically alter the single-ion and collective properties of Ho${_3}$Mg${_2}$Sb${_3}$O${_{14}}$. Our results thus highlight the crucial role played by hyperfine interactions in frustrated quantum magnets and motivate further theoretical investigations of the interplay between spin fragmentation and coherent quantum tunneling. [Reference: Z.L. Dun, X. Bai, J.A.M. Paddison, et al., arXiv:1806.04081] [Preview Abstract] |
Saturday, November 9, 2019 9:00AM - 9:30AM |
H02.00003: Understanding Geometrical Frustration in Complex Magnetic Materials Invited Speaker: Joseph Paddison Geometrical frustration -- the inability of a system to satisfy all its pairwise interactions simultaneously because of geometrical constraints -- can generate exotic states in magnetic materials, such as spin ices and quantum spin liquids [1]. The traditional route towards such states typically considers only magnetic interactions between nearest-neighbor and (sometimes) next-nearest-neighbor spins. Surprisingly, however, recent work has revealed that exotic spin-liquid states may be hosted in materials with complex exchange interactions [2,3]. In my talk, I will present neutron-scattering data and modeling results on two such materials, MgCr$_2$O$_4$ [4] and LiGaCr$_4$S$_8$ [5], and discuss the origin of the unexpected spin-liquid behavior in each case. In both materials, Cr$^{3+}$ magnetic ions occupy a frustrated lattice of corner-sharing tetrahedra, and the temperature of conventional magnetic ordering or spin freezing is strongly suppressed. I will show how the magnetic diffuse scattering observed in neutron-scattering experiments can be analyzed to determine the further-neighbor exchange interactions in these materials, providing a foundation for understanding both their spin dynamics and their magnetic ground states [4]. Finally, I will present a new open-source computer program for the refinement of spin Hamiltonians to magnetic diffuse-scattering data, to facilitate this type of analysis for a wide range of topical magnetic materials. [1] R. Moessner \& A. P. Ramirez, \emph{Physics Today} \textbf{15}, 24 (2006); [2] C. Balz \emph{et al.}, \emph{Nature Physics} \textbf{12}, 942 (2016); [3] P. Henelius \emph{et al.}, \emph{Phys. Rev. B} \textbf{93}, 024402 (2016); [4] X. Bai \emph{et al.}, \emph{Phys. Rev. Lett.} \textbf{122}, 097201 (2019); [5] G. Pokharel \emph{et al.}, \emph{Phys. Rev. B} \textbf{97}, 134117 (2018). [Preview Abstract] |
Saturday, November 9, 2019 9:30AM - 10:00AM |
H02.00004: Spin Dynamics and Hidden Plaquette ordering in the Frustrated Honeycomb Gamma Model Invited Speaker: Gia-Wei Chern I present our recent studies on a new class of highly frustrated magnets characterized by strong anisotropic spin-orbit coupling. In particular, I will focus on the so-called Gamma model in which the dominant spin interaction is given by the symmetric anisotropic, or off-diagonal, exchange process. Recently, it has been shown that a huge degeneracy exists in the ground-state manifold of the classical model. I will discuss a new classical spin liquid in which the collective flux degrees of freedom break the translation symmetry of the honeycomb lattice. We demonstrate that the system undergoes a phase transition driven by thermal order by disorder at an unusually low temperature compared with the exchange energy scale. We further compute the dynamical structure factors of the spin-liquid phase and reveal unusual dynamical properties of the hexagonal flux parameters. Finally, I will discuss effects of magnetic field on the hidden plaquette order. [Preview Abstract] |
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