NaYbS2 : A planar spin- 12 triangular-lattice magnet and putative spin liquid

Abstract

Platelike high-quality NaYbS2 rhombohedral single crystals with lateral dimensions of a few mm have been grown and investigated in great detail by bulk methods like magnetization and specific heat, but also by local probes like nuclear magnetic resonance (NMR), electron-spin resonance (ESR), muon-spin relaxation (µSR), and inelastic neutron scattering (INS) over a wide field and temperature range. Our single-crystal studies clearly evidence a strongly anisotropic quasi-2D magnetism and an emerging spin-orbit entangled S = 1/2 state of Yb towards low temperatures together with an absence of long-range magnetic order down to 260 mK. In particular, the clear and narrow Yb ESR lines together with narrow 23 Na NMR lines evidence an absence of inherent structural distortions in the system, which is in strong contrast to the related spin-liquid candidate YbMgGaO4 falling within the same space group R3m. This identifies NaYbS2 as a rather pure spin-1/2 triangular lattice magnet and a new putative quantum spin liquid.Introduction. -In low-dimensional quantum magnets, competing confined magnetic exchange interactions restrict the magnetic degrees of freedom, which leads to a strong frustration accompanied by enhanced quantum fluctuations. Ultimately this prevents the systems from longrange order, and the ground state is supposed to be a magnetic liquid. There are various types of such quantum spin liquids (QSL) depending on the lattice geometry (in 2D: square-, triangular-, kagome-, or honeycomb-type; in 3D: hyperkagome, hyperhoneycomb, or pyrochlore), the magnetic exchange (e.g. Heisenberg, Kitaev, or Dzyaloshinskii-Moriya type), and the magnetic ion itself [1][2][3][4]. Planar spin-1/2 triangular lattice magnets (TLMs) with antiferromagnetic exchange interactions are ideal QSL candidates as proposed by P. W. Anderson [5]. A few examples are found among the organic materials, such as K-(BEDT-TTF) 2 Cu 2 (CN) 3 [6] and EtnMe 4−n Sb[Pd(DMIT) 2 ] 2 [7], whereas among inorganic compounds such QSL model systems are very rare, e.g. Ba 3 CuSb 2 O 9 [8].

YbMgGaO4: A Triangular‐Lattice Quantum Spin Liquid Candidate

“…ESR spectra show the highly planar anisotropy of the Yb 3+ magnetic moments, with g ┴ = 3.19 and g ║ = 0.57 . And the gap between the ground and first‐excited CEF states is measured to be about 17 meV, much smaller than that of YbMgGaO 4 (≈39.4 meV). The small CEF gap makes the single‐ion physics mix with the many‐body‐correlated physics in the moderate temperature range, and thus the reported Curie–Weiss behavior of the susceptibilities is unobvious .…”

“…For NaYbS 2 , the single‐crystal sample is available and no long‐range magnetic transition was observed down to 260 mK . ESR spectra show the highly planar anisotropy of the Yb 3+ magnetic moments, with g ┴ = 3.19 and g ║ = 0.57 .…”

“…For NaYbS 2 , the single‐crystal sample is available and no long‐range magnetic transition was observed down to 260 mK . ESR spectra show the highly planar anisotropy of the Yb 3+ magnetic moments, with g ┴ = 3.19 and g ║ = 0.57 . And the gap between the ground and first‐excited CEF states is measured to be about 17 meV, much smaller than that of YbMgGaO 4 (≈39.4 meV).…”

Magnetic Properties of an Effective Spin-\(\frac{1}{2}\) Triangular-Lattice Compound LiYbS2

“…At temperatures considerably lower than the energy gap ∆ between the ground state and the first excited state doublet, the magnetic properties can be described by an effective spin-1 2 local moment. The values of ∆ are found to be ∼ 200, ∼400, and ∼ 180 K for NaYbS 2 [6,17], NaYbO 2 [7,8], and NaYbSe 2 [11,16], respectively. Low field studies reveal a QSL ground state with gapless excitations for both NaYbS 2 and NaYbO 2 .…”

Frustrated Magnetism in Triangular Lattice TlYbS2 Crystals Grown via Molten Flux

“…[41][42][43][44] Additionally, amongst the few delafossite-type structures reported as single crystals, synthesis typically involves the use of reactive alkali fluxes, such that the alkali metal in the flux incorporates into the final product, such as the use of KCl for KErSe2 45 or NaCl for NaYbS2. 9 For producing TlYbS2 crystals, the use of TlCl as a flux medium was ruled out due to the low solubility prohibiting ease of crystal separation upon completion of the reaction. We tried CaCl2 as a flux, and although single crystals were produced, they were of poor quality.…”