Nontrivial Fermi surface topology of the kagome superconductor CsV3Sb5 probed by de Haas-van Alphen oscillations

We have investigated the normal state Fermi-surface properties of the kagome superconductor CsV3Sb5 using torque magnetometry with applied fields (H) up to 35 T. The torque signal shows clear de Haas-van Alphen (dHvA) oscillations above 15 T. The oscillations are smooth and consist of seven distinct frequencies with values from similar to 18 T to 2135 T. The presence of higher frequencies in CsV3Sb5 is further confirmed by carrying out additional measurements using the tunnel diode oscillator technique. All frequencies measured at different tilt angles (theta) of the field direction with respect to the c axis show a 1/cos theta dependence, implying that the Fermi surfaces corresponding to these frequencies are two dimensional (2D). The absence of dHvA oscillations at theta = 90 degrees further supports the presence of 2D Fermi surfaces. The Berry phase (phi) determined from the Landau level fan diagram for all frequencies is similar to 0.4. This value is close to the theoretical value of phi = 0.5 for a nontrivial system, which strongly supports the nontrivial topology of the Fermi surfaces of these frequencies. Several quantities characterizing the Fermi surface are calculated employing the Lifshitz-Kosevich theory. These findings are crucial for exploring the interplay between nontrivial band topology, charge-density wave, and unconventional superconductivity of CsV3Sb5.