Magnetism of NaYbS2: From finite temperatures to ground state

Rare-earth chalcogenide compounds ARECh₂ (A = alkali or monovalent metal, RE = rare earth, Ch = O, S, Se, Te) are a large family of quantum spin liquid (QSL) candidate materials. NaYbS₂ is a representative member of the family. Several key issues on NaYbS₂, particularly how to determine the highly anisotropic spin Hamiltonian and describe the magnetism at finite temperatures and the ground state, remain to be addressed. In this paper, we conducted an in-depth and comprehensive study on the magnetism of NaYbS₂ from finite temperatures to the ground state. Firstly, we successfully detected three crystalline electric field (CEF) excitation energy levels using low-temperature Raman scattering technique. Combining them with the CEF theory and magnetization data, we worked out the CEF parameters, CEF energy levels, and CEF wavefunctions. We further determined a characteristic temperature of ∼40 K, above which the magnetism is dominated by CEF excitations while below which the spin-exchange interactions play a main role. The characteristic temperature has been confirmed by the temperature-dependent electron spin resonance (ESR) linewidth. Low-temperature ESR experiments on the dilute magnetic doped crystal of NaYb_0.1Lu_0.9S₂ further helped us to determine the accurate g-factor. Next, we quantitatively obtained the spin-exchange interactions in the spin Hamiltonian by consistently simulating the magnetization and specific heat data. Finally, the above studies allow us to explore the ground state magnetism of NaYbS₂ by using the density matrix renormalization group. We combined numerical calculations and experimental results to demonstrate that the ground state of NaYbS₂ is a Dirac-like QSL.