Three Dimensional Superconductivity in FeSe with Tczero Up to 10.9 K Induced by Internal Strain

Polycrystalline sample FeSe was synthesized by a self-flux solution method which shows a zero resistance temperature up to 10.9 K and a Tconset (90% \rhon, \rhon: normal state resistivity) up to 13.3 K. The decrease of superconducting transition temperature by heat treatment indicates that internal crystallographic strain which plays the same effect as external pressure is the origin of its high Tc. The fluctuation conductivity was studied which could be well described by 3D Aslamazov-Larkin (AL) power law. The estimated value of coherence length \xic=9.2 \AA is larger than the distance between conducting layers (~6.0 \AA), indicating the three-dimensional nature of superconductivity in this compound.Comment: 5 figure

Selenium‐doping induced two antiferromagnetic transitions in thiospinel compounds CuCo₂S_(4‐x)Se_x (0 ≤ x ≤ 0.8)

A series of copper thiospinels compounds, CuCo₂S_(4‐x)Se_x (x = 0, 0.2, 0.4, 0.6, 0.8), have been successfully synthesized by solid state reaction and their structure and magnetic properties have been studied. The Rietveld refinements of X‐Ray diffractions indicate that both the lattice constants and the nearest neighbor Cu‐Cu distances increase with increasing selenium doping. A weakly antiferromagnetic transition occurring at about 4 K is observed in CuCo₂S₄. Two antiferromagnetic transitions at about 3.5 K and 6 K are observed in selenium‐doped samples, which suggest that the exchange couplings associated with Cu‐S(Se)‐Cu and Cu‐Se(S)‐Cu, respectively, are responsible for the two antiferromagnetic transitions. Detailed analysis of the experimental results further indicate that the nearest‐neighbor molecular field coefficient is comparable to the next‐neighbor molecular field coefficient. We propose a reasonable model to explain this phenomenon

Pressure-induced superconductivity in topological type II Dirac semimetal NiTe₂

Very recently, NiTe₂ has been reported to be a type II Dirac semimetal with Dirac nodes near the Fermi surface. Furthermore, it is unveiled that NiTe₂ presents the Hall Effect, which is ascribed to orbital magnetoresistance. The physical properties behavior of NiTe₂ under high pressure attracts us. In this paper, we investigate the electrical properties of polycrystalline NiTe₂ by application of pressure ranging from 3.4GPa to 54.45Gpa. Superconductivity emerges at critical pressure 12GPa with a transition temperature of 3.7K, and Tc reaches its maximum, 6.4 K, at the pressure of 52.8GPa. Comparing with the superconductivity in MoP, we purposed the possibility of topological superconductivity in NiTe₂. Two superconductivity transitions are observed with pressure increasing in single crystal

AutoFP: a GUI for highly automated Rietveld refinement using an expert system algorithm based on FullProf

AutoFP, a highly automated software toolkit, has been developed to improve the extent of automation of the widely used Rietveld refinement program FullProf [Rodríguez-Carvajal (1993). Physica B, 192, 55-69]. An expert system algorithm is used as the control layer to simulate the manual process when FullProf is used to perform Rietveld refinement. This enables the program to complete the Rietveld refinement highly automatically. It is shown that the expert system algorithm is a good choice for automating Rietveld refinement. The programming interface is available for advanced users to implement their own acquired experience of refinement or add new Rietveld refinement engines to AutoFP. AutoFP can be also used as an automated Rietveld refinement engine by other programs. AutoFP is an open-source software package developed in Python, and it is user friendly, easy to learn and easy to use

Evidences for pressure-induced two-phase superconductivity and mixed structures of NiTe₂ and NiTe in type-II Dirac semimetal NiTe_(2-x) (x = 0.38 ± 0.09) single crystals

Bulk NiTe₂ is a type-II Dirac semimetal with non-trivial Berry phases associated with the Dirac fermions. Theory suggests that monolayer NiTe₂ is a two-gap superconductor, whereas experimental investigation of bulk NiTe_(1.98) for pressures (P) up to 71.2 GPa do not reveal any superconductivity. Here we report experimental evidences for pressure-induced two-phase superconductivity as well as mixed structures of NiTe₂ and NiTe in Te-deficient NiTe_(2-x) (x = 0.38±0.09) single crystals. Hole-dominant multi-band superconductivity with the P3M1 hexagonal-symmetry structure of NiTe₂ appears at P ≥ 0.5 GPa, whereas electron-dominant single-band superconductivity with the P2/m monoclinic-symmetry structure of NiTe emerges at 14.5 GPa < P < 18.4 GPa. The coexistence of hexagonal and monoclinic structures and two-phase superconductivity is accompanied by a zero Hall coefficient up to ∼ 40 GPa, and the second superconducting phase prevails above 40 GPa, reaching a maximum T_c = 7.8 K and persisting up to 52.8 GPa. Our findings suggest the critical role of Te-vacancies in the occurrence of superconductivity and potentially nontrivial topological properties in NiTe_(2-x)