Anomalous thermoelectric effects and quantum oscillations in the kagome metal CsV3Sb5

The kagome metal compounds AV3Sb5 (A = K, Rb, and Cs) feature a wealth of phenomena including nontrivial band topology, charge density wave (CDW), and superconductivity. One intriguing property is the time-reversal symmetry breaking in the CDW state without local moments, which leads to anomalous transport responses. Here, we report the investigation of magnetothermoelectric effects on high-quality CsV3Sb5 single crystals. A large anomalous Nernst effect (ANE) is observed at temperatures below 30 K and can be enhanced by the high mobility. Multiple Fermi surfaces with small effective masses are revealed by quantum oscillations in the Nernst and Seebeck signals. Furthermore, we discover a magnetic breakdown effect across the two smallest Fermi surfaces, with a gap around 20 meV between them. We propose that the two Fermi surfaces are split from a Dirac band by the CDW gap. These results indicate the large ANE originates from the CDW modulated nontrivial band structure as well as the extrinsic contributions. A second phase transition below the CDW transition temperature is also suggested by the strange temperature dependence of the ANE.