Study On Phase Transition In External Magnetic Field And Heavy-Fermion Properties In Kagome Superconductor CsV₃Sb₅

The unique structural characteristics of kagome lattice materials have attracted extensive attention in condensed matter physics.Due to the special hexagonal symmetry crystal structure,the V-based kagome metal CsV3Sb5 exhibits flat bands,Van Hove singularities and linear Dirac-like dispersion relations similar to graphene.These features induce correlated topological states and stimulate the research interest of scientists.Experimental observations show that CsV3Sb5 displays superconductivity at around 2.5 K.Below the critical temperature,there is a Hebel-Slichter coherence peak in the spin-lattice relaxation rate,which provides evidence for the s-wave superconducting character in this material.The temperature dependence of the superfluid density and electronic specific heat for CsV3Sb5 can be well fitted by the two-gap theory.Up to now,there is no consensus on the superconducting pairing mechanism for this compound,and the experimental measurements on the magnetic properties of this material have not been systematically analyzed.This paper conducts a detailed study on the superconductivity in CsV3Sb5 with the two-band Ginzburg-Landau(GL)theory.We calculate the temperature dependence of the upper critical field and magnetic penetration depth for this V-based kagome metal using the two-band GL equations.The theoretical results are consistent with the experimental data in a broad temperature range,which strongly suggests that CsV3Sb5 is a two-gap s-wave superconductor.In addition,we also discuss the variation of the London penetration depth under three different irradiation intensities with 1.3 C/cm2,3.3 C/cm2 and 8.6 C/cm2 in this compound,which indicates a gradual decrease in penetration depth value with increasing impurity concentration and the calculation results can fit the experimental measurements.Furthermore,we also note that one band of this material exhibits a heavy-fermion feature,while the other band can be regarded as a normal metal state.This suggests that CsV3Sb5 is a semi-heavy fermion superconductor with strong electronic correlations,which also explains the experimentally measured Kadowaki-Woods ratio of 0.58 ×10-5 μΩ·cm·mol2 ·K2·mJ-2.