van Hove singularities (VHS) located close to the Fermi level in kagome superconductors $A{\mathrm{V}}_3\mathrm{S}{\mathrm{b}}_5$ ($A=\mathrm{K}$, Rb, Cs) have a profound influence on their electronic and transport characteristics. Specifically, magnetotransport and susceptibility measurements on $\mathrm{Cs}{\mathrm{V}}_3\mathrm{S}{\mathrm{b}}_5$ reveal an anomalous temperature dependence of the upper critical field $H_{c2}\left(T\right)$, characterized by a pronounced upward curvature for both in-plane and $c$ axis magnetic fields, with zero-temperature $H_{c2}$ values of $\sim 6.0$ T and $\sim 1.2$ T, respectively. Our theoretical analysis, using a newly developed single-band model incorporating VHS and gap anisotropy, suggests that the observed upper critical field behavior is predominantly driven by the anisotropy of the Fermi velocity originating from VHS, instead of multiband effects or gap anisotropy. Increased electron scattering introduced by proton-irradiation defects smears out the VHS, reduces anisotropy, and recovers the conventional $H_{c2}\left(T\right)$ behavior, corroborating our proposed model.

Close

PrevNext

View figure in article

• Charge density waves
• Superconductivity
• Kagome metal
• BCS theory
• Dilution refrigerator
• Irradiation
• Semiclassical methods
• Tunnel diode resonance