Charge-density-wave-driven electronic nematicity in a kagome superconductor

Electronic nematicity, in which rotational symmetry is spontaneously broken by electronic degree of freedom, has been demonstrated as a ubiquitous phenomenon in correlated quantum fluids including high-temperature superconductors (HTS) and quantum Hall systems1,2. More strikingly, the electronic nematicity in HTS exhibits an intriguing entanglement with superconductivity, generating complicated superconducting pairing and intertwined electronic orders. Recently, an unusual competition between superconductivity and a charge-density-wave (CDW) order has been found in AV3Sb5 (A = K, Rb, Cs) family with two-dimensional vanadium kagome nets3–8. Whether these phenomena involve electronic nematicity is still elusive. Here, we report compelling evidence for the existence of electronic nematicity in CsV3Sb5, using a combination of elastoresistance measurements, nuclear magnetic resonance (NMR) and scanning tunnelling microscopy/spectroscopy (STM/S). The temperature-dependent elastoresistance coefficient (m11-m12) and NMR spectrum clearly demonstrate that, besides a C2 structural distortion of 2a0×2a0 supercell due to out-of-plane modulation, significant nematic fluctuations emerge immediately below the CDW transition (TCDW ~ 94 K) and finally a nematic transition occurs below Tnem ~ 35 K. STM experiment directly visualizes the C2-structure-pinned long-range nematic order below Tnem, suggesting a novel nematicity described by a three-state Potts model. Our findings unambiguously prove an intrinsic electronic nematicity in the normal state of CsV3Sb5, which sets a new paradigm for revealing the role of electronic nematicity on pairing mechanism in unconventional superconductors.