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.

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.

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.

Chiral Pair Density Waves with Residual Fermi Arcs in RbV_(3)Sb_(5)

The chiral 2×2 charge order has been reported and confirmed in the kagome superconductor RbV_(3)Sb_(5),while its interplay with superconductivity remains elusive owing to its lowest superconducting transition temperature Tc of about 0.85K in the AV_(3)Sb_(5) family(A=K,Rb,Cs)that severely challenges electronic spectroscopic probes.Here,utilizing dilution-refrigerator-based scanning tunneling microscopy down to 30 mK,we observe chiral 2×2 pair density waves with residual Fermi arcs in RbV_(3)Sb_(5).We find a superconducting gap of 150 μeV with substantial residual in-gap states.The spatial distribution of this gap exhibits chiral 2×2 modulations,signaling a chiral pair density wave(PDW).Our quasi-particle interference imaging of the zero-energy residual states further reveals arc-like patterns.We discuss the relation of the gap modulations with the residual Fermi arcs under the space-momentum correspondence between PDW and Bogoliubov Fermi states.