Structure and superconducting properties of Ru_(1-x)Mo_(x)(x=0.1-0.9)alloys

We report the detailed crystal structures and physical properties of Ru_(1-x)Mo_(x)alloys in the solid solution range of x=0.1-0.9.Structure characterizations indicate that the crystal structure changes from the hcp-Mg-type,toβ-CrFe-type,and then bcc-W-type.The measurements of physical properties show that the Ru_(1-x)Mo_(x)samples with x≥0.2are superconductors and the superconducting transition temperature T_c as a function of Mo content exhibits a dome-like behavior.

Pressure induced insulator to metal transition in quantum spin liquid candidate NaYbS_(2)

Pressure induced insulator to metal transition followed by the appearance of superconductivity has been observed recently in inorganic quantum spin liquid candidate NaYbSe_(2).In this paper,we study the properties of isostructural compound NaYbS_(2)under pressure.It is found that the resistance of Na YbS_(2)single crystal exhibits an insulating state below 82.9 GPa,but with a drop of more than six orders of magnitude at room temperature.Then a minimum of resistance is observed at about 100.1 GPa and it moves to lower temperature with further compression.Finally,a metallic state in the whole temperature range is observed at about 130.3 GPa accompanied by a non-Fermi liquid behavior below 100 K.The insulator to metal transition,non-monotonic resistance feature and non-Fermi liquid behavior of NaYbS_(2)under pressure are similar to those of NaYbSe_(2),suggesting that these phenomena might be the universal properties in NaLnCh_(2)(Ln=rare earth,Ch=O,S,Se)system.

Superconductivity and Normal-State Properties of Kagome Metal RbV_(3)Sb_(5) Single Crystals

We report the discovery of superconductivity and detailed normal-state physical properties of RbV_(3)Sb_(5) single crystals with V kagome lattice.RbV_(3)Sb_(5) single crystals show a superconducting transition at Tc~0.92 K.Meanwhile,resistivity,magnetization and heat capacity measurements indicate that it exhibits anomalies of properties at T*~102-103 K,possibly related to the formation of charge ordering state.When T is lower than T*,the Hall coefficient RH undergoes a drastic change and sign reversal from negative to positive,which can be partially explained by the enhanced mobility of hole-type carriers.In addition,the results of quantum oscillations show that there are some very small Fermi surfaces with low effective mass,consistent with the existence of multiple highly dispersive Dirac band near the Fermi energy level.

S-Wave Superconductivity in Kagome Metal CsV_(3)Sb_(5) Revealed by ^(121/123)Sb NQR and ^(51)V NMR Measurements

We report ^(121/123)Sb nuclear quadrupole resonance(NQR)and ^(51)V nuclear magnetic resonance(NMR)measurements on kagome metal CsV_(3)Sb_(5) with T_(c)=2.5 K.Both ^(51)V NMR spectra and ^(121/123)Sb NQR spectra split after a charge density wave(CDW)transition,which demonstrates a commensurate CDW state.The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first-order phase transition.At low temperature,electric-field-gradient fluctuations diminish and magnetic fluctuations become dominant.Superconductivity emerges in the charge order state.Knight shift decreases and 1/T_(1)T shows a Hebel–Slichter coherence peak just below T_(c),indicating that CsV_(3)Sb_(5) is an s-wave superconductor.

Superconductivity in Kagome Metal YRu_(3)Si_(2)with Strong Electron Correlations

We report the detailed physical properties of YRu_(3)Si_(2)with the Ru kagome lattice at normal and superconducting states.The results of resistivity and magnetization show that YRu_(3)Si_(2)is a type-II bulk superconductor with T_(c)~3.0 K.The specific heat measurement further suggests that this superconductivity could originate from the weak or moderate electron-phonon coupling.On the other hand,both large Kadawaki–Woods ratio and Wilson ratio indicate that there is a strong electron correlation effect in this system,which may have a connection with the featured flat band of kagome lattice.

Tri-hexagonal charge order in kagome metal CsV_(3)Sb_(5) revealed by (121)Sb nuclear quadrupole resonance

We report ^(121)Sb nuclear quadrupole resonance(NQR)measurements on kagome superconductor CsV_(3)Sb_(5) with Tc=2.5 K.^(121)Sb NQR spectra split after a charge density wave(CDW)transition at 94 K,which demonstrates a commensurate CDW state.The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first order phase transition.The CDW order exhibits tri-hexagonal deformation with a lateral shift between the adjacent kagome layers,which is consistent with 2×2×2 superlattice modulation.The superconducting state coexists with CDW order and shows a conventional s-wave behavior in the bulk state.

Structures and Physical Properties of V-Based Kagome Metals CsV_(6)Sb_(6)and Cs V_(8)Sb_(12)

We report two new members of V-based kagome metals CSV_(6)Sb_(6)and CsV_(8)Sb_(12).The most striking structural feature of CSV_(6)Sb_(6)is the V kagome bilayers.For CsV_(8)Sb_(12),there is an intergrowth of two-dimensional V kagome layers and one-dimensional V chains,and the latter ones lead to the orthorhombic symmetry of this material.Further measurements indicate that these two materials exhibit metallic and Pauli paramagnetic behaviors.More importantly,different from CSV_(3) Sb_(5),the charge density wave state and superconductivity do not emerge in CSV_(6)Sb_(6)and CsV_(8)Sb_(12)when temperature is above 2 K.Small magnetoresistance with saturation behavior and linear field dependence of Hall resistivity at high field and low temperature suggest that the carriers in both materials should be uncompensated with much different concentrations.The discovery of these two new V-based kagome metals sheds light on the exploration of correlated topological materials based on kagome lattice.

Distinct superconducting behaviors of pressurized WB2 and ReB2 with different local B layers

The recent discovery of superconductivity up to 32 K in the pressurized MoBreignites the interest in exploring high-Tc superconductors in transition-metal diborides. Inspired by that work, we turn our attention to the 5 d transition-metal diborides.Here we systematically investigate the responses of both structural and physical properties of WBand ReBto external pressure,which possess different types of boron layers. Similar to MoB, the pressure-induced superconductivity was also observed in WBabove 60 GPa with a maximum Tcof 15 K at 100 GPa, while no superconductivity was detected in ReBin this pressure range. Interestingly, the structures at ambient pressure for both WBand ReBpersist to high pressure without structural phase transitions. Theoretical calculations suggest that the ratio of flat boron layers in this class of transition-metal diborides may be crucial for the appearance of high Tc. The combined theoretical and experimental results highlight the effect of the geometry of boron layers on superconductivity and shed light on the exploration of novel high-Tcsuperconductors in borides.