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].

High-quality single crystals of NaYbSe2, which resembles a perfect triangular-lattice antiferromagnet without the intrinsic disorder, are investigated by magnetization and specific-heat, as well as the local probe techniques nuclear magnetic resonance (NMR) and electron spin resonance (ESR). The low-field measurements confirm the absence of any spin freezing or long-range magnetic order down to 50 mK, which suggests a quantum spin liquid ground (QSL) state with gapless excitations. Instability of the QSL state is observed upon applying magnetic fields. For the H⊥c direction, a field-induced magnetic phase transition is observed above 2 T from the Cp(T ) data, agreeing with a clear Ms 3 plateau of M (H), which is associated with an up-up-down (uud) spin arrangement. For the H c direction, a field-induced transition could be evidenced at a much higher field range (9 -21 T). The 23 Na NMR measurements provide microscopic evidence for field-induced ordering for both directions. A reentrant behaviour of TN, originating from the thermal and quantum spin fluctuations, is observed for both directions. The anisotropic exchange interactions J ⊥ 4.7 K and Jz 2.33 K are extracted from the modified bond-dependent XXZ model for the spin-1 2 triangular-lattice antiferromagnet. The absence of magnetic long-range order at zero fields is assigned to the effect of strong bond-frustration, arising from the complex spin-orbit entangled 4f ground state. Finally, we derive the highly anisotropic magnetic phase diagram, which is discussed in comparison with the existing theoretical models for spin-1 2 triangular-lattice antiferromagnets. :1911.12712v1 [cond-mat.str-el] arXiv

Rare-earth delafossites were recently proposed as promising candidates for the realization of an effective S = 1/2 quantum spin liquid (QSL) on the triangular lattice. In contrast to the most actively studied triangular-lattice antiferromagnet YbMgGaO4, which is known for considerable structural disorder due to site intermixing, NaYbS2 delafossite realizes structurally ideal triangular layers. We present detailed µSR studies on this regular (undistorted) triangular Yb sublattice based system with effective spin J eff = 1/2 in the temperature range 0.05 -40 K. Zero-field (ZF) and longitudinal field (LF) µSR studies confirm the absence of any long range magnetic order state down to 0.05 K (∼ J/80). Current µSR results together with the so far available bulk characterization data suggest that NaYbS2 is an ideal candidate to identify QSL ground state.

The delafossite structure of NaYbS 2 contains a planar spin-1/2 triangular lattice of Yb 3+ ions and features a possible realisation of a quantum spin-liquid state. We investigated the Yb 3+ spin dynamics by Electron Spin Resonance (ESR) in singlecrystalline samples of NaYbS 2 . Very clear spectra with a well-resolved and large anisotropy could be observed down to the lowest accessible temperature of 2.7 K. In contrast to the ESR properties of other known spin-liquid candidate systems, the resonance seen in NaYbS 2 is accessible at low fields (< 1T) and is narrow enough for accurate characterisation of the relaxation rate as well as the g factor of the Yb 3+ spins.arXiv:1812.07871v1 [cond-mat.str-el]

Recently, several putative quantum spin liquid (QSL) states were discovered in {\tilde S} = 1/2S̃=1/2 rare-earth based triangular-lattice antiferromagnets (TLAF) with the delafossite structure. In order to elucidate the conditions for a QSL to arise, we report here the discovery of a long-range magnetic order in the Ce-based TLAF KCeS_22 below T_{\mathrm N} = 0.38TN=0.38 K, despite the same delafossite structure. Finally, combining various experimental and computational methods, we characterize the crystal electric field scheme, the magnetic anisotropy and the magnetic ground state of KCeS_22.

No abstract

We investigated the spin dynamics by electron spin resonance (ESR) of the Yb-based, effective spin-1/2 delafossites NaYbO 2 , AgYbO 2 , LiYbS 2 , NaYbS 2 , and NaYbSe 2 which all show an absence of magnetic order down to lowest reachable temperatures and thus are prime candidates to host a quantum spin-liquid ground state in the vicinity of long range magnetic order. Clearly resolved ESR spectra allow to obtain well-defined g values which are determined by the crystal field of the distorted octahedral surrounding of the Yb-ions in trigonal symmetry. This local crystal field information provides important input to characterize the effective S = 1/2 Kramers doublet as well as the anisotropic exchange coupling between the Yb ions which is crucial for the nature of the groundstate. The ESR linewidth ∆B is characterised by the spin dynamics and is mainly determined by the anisotropic exchange coupling. We discuss and compare ∆B of the above mentioned delafossites focussing on the low temperature behaviour which is dominated by the growing influence of spin correlations.

Here, we report the synthesis and magnetic properties of a Yb-based triangular-lattice compound LiYbS 2 . At low temperatures, it features an effective spin-1 2 state due to the combined effect of crystal electric field and spin orbit coupling. Magnetic susceptibility measurements and 7 Li nuclear magnetic resonance experiments reveal the absence of magnetic long range ordering down to 2 K, which suggests a possible quantum spin liquid ground state. A dominant antiferromagnetic nearest neighbour exchange interaction J/k B 5.3 K could be extracted form the magnetic susceptibility. The NMR linewidth analysis yields the coupling constant between the Li nuclei and Yb 3+ ions which was found to be purely dipolar in nature.