Spinon Fermi surface spin liquid in a triangular lattice antiferromagnet NaYbSe2

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 crystalline 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. By comparing the structure of our magnetic excitation spectra with the theoretical expectation from the spinon continuum, we conclude that the ground state of NaYbSe2 is a QSL with a spinon Fermi surface.

Fluctuating magnetic droplets immersed in a sea of quantum spin liquid

“…1c. Consistent with magnetic susceptibility and former reports 43,45 , no sharp anomaly of LRO is observed in NaYbSe2. With decreasing temperature, a broad hump of specific heat shows up, whose position shifts to higher temperature in magnetic field.…”

“…2d. As guided by the red dashed line, the temperature independent behavior of CMag/T below 0.25 K is consistent with a spinon Fermi surface 45 . By integrating CMag/T, we obtain the magnetic entropy SMag, as shown in Fig.…”

“…Including CsYbSe2 with the same structure, all of them have field-induced magnetic orders 38,[41][42][43][44] . Very recently, the ground state of NaYbSe2 is claimed to be a QSL with spinon Fermi surface 45 . Pressure-induced superconductivity is also observed in NaYbSe2 46,47 , opening up a promising way to study the mechanism of superconductivity in QSL candidates.…”

“…Additionally, there is only less than 5.2% residual entropy at zero temperature, also indicating the presence of QSL. Now it brings us to why other methods like magnetic susceptibility and neutron scattering do not observe such ferrimagnetic droplets 36,45 . For magnetic susceptibility technique, it is more sensitive to slower fluctuations, whose limit is about 10 4 Hz, while NMR and µSR are more sensitive to faster fluctuations.…”

Low-energy Spin Dynamics of Quantum Spin Liquid Candidate $NaYbSe_{2}$

“…Introduction-Recently revealed triangular lattice rare earth chalcogenides form a large family of quantum spin liquid (QSL) candidates [1][2][3][4]. The strong spin-orbit coupling (SOC) and crystalline electronic field (CEF) excitations generate a rich diversity of magnetic and electronic properties of the family and have been extensively investigated [2,[5][6][7][8][9][10].…”