Abstract
Triangular lattice of rare-earth ions with interacting effective spin-1/2 local moments is an ideal platform to explore the physics of quantum spin liquids (QSLs) in the presence of strong spin-orbit coupling, crystal electric fields, and geometrical frustration. The Yb delafossites, NaYbCh2 (Ch=O, S, Se) with Yb ions forming a perfect triangular lattice, have been suggested to be candidates for QSLs. Previous thermodynamics, nuclear magnetic resonance, and powder-sample neutron scattering measurements on NaYbCh2 have supported the suggestion of the QSL ground states. The key signature of a QSL, the spin excitation continuum, arising from the spin quantum number fractionalization, has not been observed. Here we perform both elastic and inelastic neutron scattering measurements as well as detailed thermodynamic measurements on high-quality single-crystal NaYbSe2 samples to confirm the absence of long-range magnetic order down to 40 mK, and further reveal a clear signature of magnetic excitation continuum extending from 0.1 to 2.5 meV. The comparison between the structure of the magnetic excitation spectra and the theoretical expectation from the spinon continuum suggests that the ground state of NaYbSe2 is a QSL with a spinon Fermi surface.
| Original language | English |
|---|---|
| Article number | 021044 |
| Journal | Physical Review X |
| Volume | 11 |
| Issue number | 2 |
| DOIs | |
| State | Published - Jun 2021 |
Funding
We thank M. Stone for suggestions of appropriate neutron scattering instrumentation, and Feng Ye (ORNL) for the assistance with the single-crystal x-ray diffraction measurements. We also thank Ling Wang and Yuesheng Li for helpful discussions. The research at Beijing Normal University is supported by the National Natural Science Foundation of China (Grants No. 11734002 and No. 11922402). The work at ShanghaiTech university is supported by the National Natural Science Foundation of China (No. 11874264, Y. Guo). Y. Guo and X. W. thank the support from Analytical Instrumentation Center (No. SPST-AIC10112914), SPST, ShanghaiTech University. The neutron scattering work at Rice is supported by U.S. DOE BES DE-SC0012311 (P. D.). This work is further supported by funds from the Ministry of Science and Technology of China (Grants No. 2016YFA0301001, No. 2018YFGH000095, No. 2016YFA0300500 for G. C., and Grants No. 2016YFA0300501 and No. 2016YFA0300503 for L. S. and G. C.) and from the Research Grants Council of Hong Kong with General Research Fund Grant No. 17303819 (G. C.). E. F. and H. C. acknowledges support of U.S. DOE BES Early Career Award No. KC0402010 under Contract No. DE-AC05-00OR22725. E. M. and C.-L. H. acknowledge support from U.S. DOE BES DE-SC0019503. This research used resources at Spallation Neutron Source, a U.S. DOE Office of Science User Facility operated by ORNL. We gratefully acknowledge the Science and Technology Facilities Council (STFC) for access to neutron beam time at ISIS.