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Quantum spin liquid (QSL) is a novel state of matter which refuses the conventional spin freezing even at 0 K. Experimentally searching for the structurally perfect candidates is a big challenge in condensed matter physics. Here we report the successful synthesis of a new spin-1/2 triangular antiferromagnet YbMgGaO4 with symmetry. The compound with an ideal two-dimensional and spatial isotropic magnetic triangular-lattice has no site-mixing magnetic defects and no antisymmetric Dzyaloshinsky-Moriya (DM) interactions. No spin freezing down to 60 mK (despite θw ~ −4 K), the power-law temperature dependence of heat capacity and nonzero susceptibility at low temperatures suggest that YbMgGaO4 is a promising gapless (≤|θw|/100) QSL candidate. The residual spin entropy, which is accurately determined with a non-magnetic reference LuMgGaO4, approaches zero (<0.6%). This indicates that the possible QSL ground state (GS) of the frustrated spin system has been experimentally achieved at the lowest measurement temperatures. [ABSTRACT FROM AUTHOR]

High-quality epitaxial LaCoO 3 (LCO) thin films have been deposited on SrTiO 3 (STO) substrates with pulsed laser deposition (PLD). We find that the LCO films undergo a typical ferromagnetic-paramagnetic (FM-PM) phase transition at ∼80 K. To understand the nature of magnetic phase transition, various methods, including the modified Arrott plot and critical isotherm analysis, were used to determine the critical exponents, which are β = 0.754(1) with a Curie temperature T C = 79.8(8) K and γ = 1.52(2) with T C = 79.9(2) K. The reliability of these critical exponents was confirmed using the Widom scaling relation and the scaling hypothesis. Further analysis revealed that the spin coupling within the LCO films exhibits two-dimensional (2D) long-range magnetic interaction and the magnetic exchange distance decays as J(r) ∼r -(3.46) . Our critical behavior analysis may shed new light on the further understanding of the origin of FM and the relatively fixed T C in LCO thin films.

Topological Weyl semimetals (TWSs) with pairs of Weyl points and topologically protected Fermi arc states have broadened the classification of topological phases and provide superior platform for study of topological superconductivity. Here we report the nontrivial superconductivity and topological features of sulfur-doped T d -phase MoTe 2 with enhanced T c compared with type-II TWS MoTe 2 It is found that T d -phase S-doped MoTe 2 (MoTe 2- x S x , x ∼ 0.2) is a two-band s -wave bulk superconductor (∼0.13 meV and 0.26 meV), where the superconducting behavior can be explained by the s +- pairing model. Further, measurements of the quasi-particle interference (QPI) patterns and a comparison with band-structure calculations reveal the existence of Fermi arcs in MoTe 2- x S x More interestingly, a relatively large superconducting gap (∼1.7 meV) is detected by scanning tunneling spectroscopy on the sample surface, showing a hint of topological nontrivial superconductivity based on the pairing of Fermi arc surface states. Our work demonstrates that the T d -phase MoTe 2- x S x is not only a promising topological superconductor candidate but also a unique material for study of s +- superconductivity., Competing Interests: The authors declare no conflict of interest.

The substitution of magnetic Fe(2+) for nonmagnetic Cu(+) in the Cu(1-x)Fe(x)Ir(2)S(4) system causes drastic changes in electromagnetic behavior. For x = 0.01 and 0.025, the Peierls-like phase transition step ΔM in magnetization increases with x increasing, and an unexpected spin transition occurs at T(*)≈120 K. This may be attributed to the spin-polarization of the Ir(4+) ions by the Fe(2+) ions. When x exceed 0.1, the Peierls-like phase transition is suppressed completely. The magnetic state for Fe doped samples transforms from ferromagnetic (FM) to paramagnetic (PM), and back to the FM state again with the increase of x. For the highly doped samples, the FM domains formed by Fe(2+) ions result in another transition at T(**)≈110 K and the cluster-spin glass transition.