Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session T29: Identifying Magnetic Ground States and Impurities in Quantum Spin Liquid CandidatesInvited Live Streamed
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Sponsoring Units: GMAG DCMP Chair: Stewart Brown, UCLA Room: McCormick Place W-190B |
Thursday, March 17, 2022 11:30AM - 12:06PM |
T29.00001: Disorder, Quantum Spin Liquids, and Valence Bond Crystals Invited Speaker: Michael R Norman Quantum spin liquids are novel states of matter that exhibit long range entanglement and associated topological properties despite the absence of traditional long range order in the Landau sense. Whether such states exist in nature or not is an unresolved matter. Relevant to this discussion is disorder that always exists in real materials. Here, I will review evidence for quantum spin liquid behavior in several candidate materials, and then comment on the effect of disorder on their properties. I will then contrast theories that address their novel properties based on either intrinsic QSL physics, or more traditional approaches based on random exchange. I will close by contrasting QSL ground states with valence bond ones, and how this is influenced by disorder. |
Thursday, March 17, 2022 12:06PM - 12:42PM |
T29.00002: Gapped magnetic ground state in quantum-spin-liquid candidate κ-(BEDT-TTF)2Cu2(CN)3 Invited Speaker: Martin Dressel Geometrical frustration, quantum entanglement, and disorder may prevent long-range order of localized spins with strong exchange interactions, resulting in an exotic state of matter. κ-(BEDT-TTF)2Cu2(CN)3 is considered the prime candidate for this elusive quantum spin liquid state on a triangular lattice, but its ground-state properties remain puzzling. It is not clear in which way disorder affects the measured electronic ground state in one or the other way. At 6 K an enigmatic anomaly has been observed in various physical properties that triggered speculations in many directions. On the fundamental issue of the existence of a spin gap, conflicting conclusions have been drawn from magnetic torque, μSR, NMR, thermal transport and specific heat measurements. In contrast to these indirect methods, electron spin resonance (ESR) directly probes the magnetic excitation spectrum of the conduction electrons, which allows us to unambiguously identify the intrinsic response and separate it from other contributions. For that reason, we developed a broadband ultra-low-temperature ESR technique based on coplanar waveguide resonators. |
Thursday, March 17, 2022 12:42PM - 1:18PM |
T29.00003: Contrasting Scenarios for Organic Spin Liquids Invited Speaker: Stephen Winter The ultimate ground state of organic spin-liquid candidates, such as κ-(ET)2Cu2(CN)3 has long remained elusive. While a variety of apparently conflicting experimental results have favored various scenarios over the years, a comprehensive view has yet to emerge. It has long been thought that conventional magnetic order is destabilized by strong ring-exchange, occasioned by proximity to the Mott transition. Such interactions are known to promote either chiral spin-liquid phases or unconventional spin-vortex order if sufficiently strong. On the one hand, this scenario is now supported by the recent observation of spin-vortex order in the related compound κ-(BETS)2Mn[N(CN)2]3, which definitely confirms the importance of ring-exchange. On the other hand, there is mounting evidence for an important role of disorder in the low-temperature response. Here, we contrast these scenarios in view of recent experimental results. |
Thursday, March 17, 2022 1:18PM - 1:54PM |
T29.00004: 17-O NMR site-selective study of the quantum kagome antiferromagnet ZnCu3(OH)6Cl2 : a gapless ground state. Invited Speaker: Philippe Mendels Herbertsmithite ZnCu3(OH)6Cl2 is known as one of the most emblematic and deeply studied quantum spin liquid representative of the Quantum Kagome Heisenberg Antiferromagnet Hamiltonian physics. On the theory side, the ground state has been heavily debated for more than 30 years with no definitive solution to-date. Yet, defects, have been ubiquitous in all experiments so far and one of the key issues is to disentangle what would be the intrinsic physics of an isolated kagome plane and that impacted by 20-30% interlayer Cu’s replacing non-magnetic Zn2+. At this stage, the need of including defects - but which defects? - into models represents a difficult task but one of the most promising avenues to conclude on the ground state of the KHAF. |
Thursday, March 17, 2022 1:54PM - 2:30PM |
T29.00005: Emergence of spin singlets with inhomogeneous gaps in the kagome lattice Heisenberg antiferromagnets ZnCu3(OD)6FBr and ZnCu3(OD)6Cl2 Invited Speaker: Jiaming Wang The kagome Lattice Heisenberg Antiferromagnet (KLHA) formed from a corner-sharing triangular lattice of frustrated spins serves as one of the best candidates in the search for a quantum spin liquid ground state. Zn-barlowite (ZnCu3(OD)6FBr) and herbertsmithite (ZnCu3(OD)6Cl2) are two highly promising realizations of the KLHA and have been shown to remain paramagnetic even at T ≈ 10-4J, where J ≈ 190 K is the Cu-Cu super-exchange interaction energy. However, the reproducible contributions from interlayer defects obscure the intrinsic behavior, thus making theoretical predictions difficult to verify. In this presentation, we will explain how 63Cu and 79Br nuclear quadrupole resonance and 19F nuclear magnetic resonance were used along with inverse Laplace transform T1 analysis to locally probe the quantum ground states of these kagome materials and elucidate the nature of their magnetic inhomogeneity. We present direct evidence for the gradual emergence of spin singlets with spatially varying excitation gaps and show that their fraction is limited to ~60% even at temperatures far below J. |
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