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Title: Strong quantum fluctuations in a quantum spin liquid candidate with a Co-based triangular lattice

Abstract

Currently under active study in condensed matter physics, both theoretically and experimentally, are quantum spin liquid (QSL) states, in which no long-range magnetic ordering appears at low temperatures due to strong quantum fluctuations of the magnetic moments. The existing QSL candidates all have their intrinsic disadvantages, however, and solid evidence for quantum fluctuations is scarce. Here, we report a previously unreported compound, Na2BaCo(PO4)2, a geometrically frustrated system with effective spin-1/2 local moments for Co2+ ions on an isotropic 2-dimensional (2D) triangular lattice. Magnetic susceptibility and neutron scattering experiments show no magnetic ordering down to 0.05 K. Thermodynamic measurements show that there is a tremendous amount of magnetic entropy present below 1 K in 0-applied magnetic field. The presence of localized low-energy spin fluctuations is revealed by inelastic neutron measurements. At low applied fields, these spin excitations are confined to low energy and contribute to the anomalously large specific heat. In larger applied fields, the system reverts to normal behavior as evident by both neutron and thermodynamic results. Our experimental characterization thus reveals that this material is an excellent candidate for the experimental realization of a QSL state.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Institute for Quantum Matter (IQM); Johns Hopkins Univ., Baltimore, MD (United States)
Sponsoring Org.:
USDOE Office of Science (SC); National Institute of Standards and Technology; US Department of Commerce; Gordon and Betty Moore Emergent Phenomena in Quantum System (EPiQS) Program
OSTI Identifier:
1564522
Alternate Identifier(s):
OSTI ID: 1613182; OSTI ID: 1825715
Grant/Contract Number:  
SC0019331; GBMF-4412
Resource Type:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 116 Journal Issue: 29; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; science & technology - other topics; quantum spin liquids; geometric frustrated magnets; quantum fluctuation; triangular lattice

Citation Formats

Zhong, Ruidan, Guo, Shu, Xu, Guangyong, Xu, Zhijun, and Cava, Robert J. Strong quantum fluctuations in a quantum spin liquid candidate with a Co-based triangular lattice. United States: N. p., 2019. Web. doi:10.1073/pnas.1906483116.
Zhong, Ruidan, Guo, Shu, Xu, Guangyong, Xu, Zhijun, & Cava, Robert J. Strong quantum fluctuations in a quantum spin liquid candidate with a Co-based triangular lattice. United States. https://doi.org/10.1073/pnas.1906483116
Zhong, Ruidan, Guo, Shu, Xu, Guangyong, Xu, Zhijun, and Cava, Robert J. Tue . "Strong quantum fluctuations in a quantum spin liquid candidate with a Co-based triangular lattice". United States. https://doi.org/10.1073/pnas.1906483116.
@article{osti_1564522,
title = {Strong quantum fluctuations in a quantum spin liquid candidate with a Co-based triangular lattice},
author = {Zhong, Ruidan and Guo, Shu and Xu, Guangyong and Xu, Zhijun and Cava, Robert J.},
abstractNote = {Currently under active study in condensed matter physics, both theoretically and experimentally, are quantum spin liquid (QSL) states, in which no long-range magnetic ordering appears at low temperatures due to strong quantum fluctuations of the magnetic moments. The existing QSL candidates all have their intrinsic disadvantages, however, and solid evidence for quantum fluctuations is scarce. Here, we report a previously unreported compound, Na2BaCo(PO4)2, a geometrically frustrated system with effective spin-1/2 local moments for Co2+ ions on an isotropic 2-dimensional (2D) triangular lattice. Magnetic susceptibility and neutron scattering experiments show no magnetic ordering down to 0.05 K. Thermodynamic measurements show that there is a tremendous amount of magnetic entropy present below 1 K in 0-applied magnetic field. The presence of localized low-energy spin fluctuations is revealed by inelastic neutron measurements. At low applied fields, these spin excitations are confined to low energy and contribute to the anomalously large specific heat. In larger applied fields, the system reverts to normal behavior as evident by both neutron and thermodynamic results. Our experimental characterization thus reveals that this material is an excellent candidate for the experimental realization of a QSL state.},
doi = {10.1073/pnas.1906483116},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 29,
volume = 116,
place = {United States},
year = {2019},
month = {7}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
https://doi.org/10.1073/pnas.1906483116

Citation Metrics:
Cited by: 33 works
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Figures / Tables:

Fig. 1 Fig. 1: The crystal structure of Na2BaCo(PO4)2. (A) The crystal structure for Na2BaCo(PO4)2 based on the packing of M-O polyhedra. (B) The triangular layer of CoO6 octahedra in the ab plane, with J1 and J2 marked to indicate the superexchange coupling between the nearest neighbor Co 2+ ions in themore » same plane and the neighboring plane. (C) View emphasizing the layers of CoO6 octahedra along the c axis viewed from the b axis. (D) Top view of the relative orientation of the CoO6 and other groups in the 2D triangular layers. The lines in C and D indicate the unit cell. (E) Photo of the pink single crystals of Na2BaCo(PO4)2.« less

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.