High quantum oscillation frequencies and nontrivial topology in kagome superconductor KV3Sb5 probed by torque magnetometry up to 45 T

Here, we present the Fermi surface properties of the kagome superconductor KV3Sb5 using torque magnetom-etry at applied fields up to 45 T and temperatures down to that of liquid 3He (0.32 K). The torque signal shows clear de Haas-van Alphen (dHvA) oscillations with 14 major frequencies ranging from similar to 33 to 2149 T, nine of which are higher frequencies (above 500 T) that have never been reported in KV3Sb5. Angular dependence measurements of the dHvA oscillations were carried out to investigate the dimensionality of the Fermi surface. Based on our analysis, several frequencies follow the 1/cos 0 dependence, where 0 is the tilt angle with respect to the applied field direction and oscillations disappear above 0 = 60 degrees, which suggest that Fermi surfaces corresponding to these frequencies are quasitwo dimensional. The Berry phase (GB), determined by constructing a Landau level fan diagram, was found to be (1.B similar to it, which strongly suggests the nontrivial topology of KV3Sb5. To explain the experimental results, we carried out band-structure and Fermi-surface calculations using density functional theory (DFT) for both pristine and charge-density wave (CDW) phases. We found that the Fermi surface undergoes severe reconstruction in the CDW phase and, more importantly, our calculation results are in reasonable agreement with the experimentally measured Fermi-surface frequencies. The observation in this paper of very high quantum oscillation frequencies in KV3Sb5 and the determination of their detailed Fermi-surface properties, along with the analyses of corresponding DFT calculation results, are crucial for understanding CDW order, unconventional superconductivity, and nontrivial topology in AV3Sb5 (A = K, Rb, and Cs), as well as the interplay among them.