Valence Bond Glass Ground State and Gapped Itinerant Excitations in a Frustrated Quantum Magnet

ORAL

Abstract

The experimental observation of the quantum spin liquid (QSL) has been challenging and contentious. This is largely due to an overly simplistic classification of real-world magnetic systems as either conventionally long-range ordered (LRO)—with minimal spin entanglement—or as fully entangled QSLs. We contend that this binary categorization is insufficient.

Our measurements of specific heat and thermal conductivity on NaYbxLu1-xSe2, a magnetic-site-dilution of the QSL candidate NaYbSe2, suggest that the spin ground state of NaYbSe2 is in fact a valence bond glass (VBG). This state is spatially inhomogeneous and exhibits a diverse range of entanglement length scales. The VBG model successfully resolves a long-standing paradox: while specific heat and inelastic neutron scattering (INS) measurements reveal dispersed gapless excitations in various materials, thermal conductivities show gapped itinerant magnetic excitations universally. By tracking phonon thermal conductivities of NaYbxLu1-xSe2 across a broad temperature range, we propose that spin-induced quenched lattice randomness is responsible for the spatial inhomogeneity that ultimately leads to the VBG ground state [Lyu 2025].

*This work was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division under contract DEAC02-05-CH11231 within the Quantum Materials program (KC2202). L.P.C., Y.L., K.N. and J.G.A. were supported by the EPiQS Initiative of the Gordon and Betty Moore Foundation through grant No. GBMF9067. J.R. was supported by the Quantum Materials program (KC2202) at the Lawrence Berkeley National Laboratory. C.L. acknowledges the fellowship support from the Gordon and Betty Moore Foundation through the Emergent Phenomena in Quantum Systems (EPiQS) program. Work at the National High Magnetic Field Laboratory was supported by NSF Cooperative Agreements No. DMR-1644779 and No. DMR-2128556, the DOE, and the State of Florida. J.S. acknowledges support from the DOE Basic Energy Sciences FWP "Science of 100 T".

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Publication: Y. Lyu, L. Pritchard Cairns, J. Rodriguez, C. Liu, K. Ng, J. Singleton, and J. G. Analytis. "Entanglement Randomness and Gapped Itinerant Carriers in a Frustrated Quantum Magnet" in Physical Review X (2025). DOI: 10.1103/tx6t-gbxy.

Presenters

  • Yuanqi Lyu

    • University of California, Berkeley

Authors

  • Yuanqi Lyu

    • University of California, Berkeley

  • Luke S Pritchard Cairns

    • University of California, Berkeley

  • Josue Rodriguez

    • University of California Berkeley

  • Chunxiao Liu

    • University of California, Berkeley

  • Kenneth Ng

    • University of California, Berkeley

  • John Singleton

    • NHMFL / LANL
    • Los Alamos National Laboratory (LANL)

  • James G Analytis

    • University of California, Berkeley