S-Wave Superconductivity in Kagome Metal CsV<sub>3</sub>Sb<sub>5</sub> Revealed by <sup>121/123</sup>Sb NQR and <sup>51</sup>V NMR Measurements
Chao Mu, Qiangwei Yin, Zhijun Tu, Chunsheng Gong, Hechang Lei, Zheng Li, Jianlin Luo
Abstract
We report 121/123 Sb nuclear quadrupole resonance (NQR) and 51 V nuclear magnetic resonance (NMR) measurements on kagome metal CsV 3 Sb 5 with T c = 2.5 K. Both 51 V NMR spectra and 121/123 Sb NQR spectra split after a charge density wave (CDW) transition, which demonstrates a commensurate CDW state. The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first-order phase transition. At low temperature, electric-field-gradient fluctuations diminish and magnetic fluctuations become dominant. Superconductivity emerges in the charge order state. Knight shift decreases and 1/ T 1 T shows a Hebel–Slichter coherence peak just below T c , indicating that CsV 3 Sb 5 is an s-wave superconductor.