Tuning the competition between superconductivity and charge order in the kagome superconductor Cs(V1-xNbx)3Sb5

The recently discovered coexistence of superconductivity and charge-density wave order in the kagome systems AV3Sb5 (A = K, Rb, Cs) has stimulated enormous interest. It is predicted that a vanadium-based kagome system may host a flat band, nontrivial linear dispersive Dirac surface states, and electronic correlation. Although much research has been carried out, the origin of the charge-density wave (CDW) order, the relationship between the superconductivity and the CDW, and whether the anomalous Hall effect (AHE) arises primarily from the kagome lattice or the CDW order, remain controversial. Here, we report an extensive investigation of Cs(V1-xNbx)3Sb5 samples with systematic Nb doping. Our results show that the Nb doping induces apparent suppression of CDW order and promotes superconductivity; meanwhile, the AHE and magnetoresistance (MR) are weakened significantly together with the CDW order. Combining with density-functional calculations, we interpret these effects by an antiphase shift of the Fermi energy with respect to the saddle points near M and the Fermi surface centered around ??. It is found that the former depletes the filled states for the CDW instability and worsens the nesting condition for CDW order, while the latter lifts the Fermi level upward and enlarges the Fermi surface surrounding the I' point, and thus promotes superconductivity. Our results uncover a delicate but unusual competition between the CDW order and superconductivity.

Automated summary

The coexistence of superconductivity and charge-density wave (CDW) order in kagome systems has sparked great interest. In this study, Cs(V1-xNbx)3Sb5 samples with systematic Nb doping were extensively investigated, and it was found that Nb doping leads to the suppression of CDW order and the promotion of superconductivity. Additionally, the anomalous Hall effect (AHE) and magnetoresistance (MR) were significantly weakened along with the CDW order. The effects were interpreted through density-functional calculations and antiphase shifts of the Fermi energy near saddle points and a Fermi surface reorganization. The results uncovered a delicate and unusual competition between CDW order and superconductivity.