Superconductivity under pressure in a chromium-based kagome metal.

Abstract

Superconductivity in a highly correlated kagome system has been theoretically proposed for years (refs. ^1-5), yet the experimental realization is hard to achieve^6,7. The recently discovered vanadium-based kagome materials⁸, which exhibit both superconductivity^9-11 and charge-density-wave orders^12-14, are nonmagnetic^8,9 and weakly correlated^15,16. Thus these materials are unlikely to host the exotic superconductivity theoretically proposed. Here we report the discovery of a chromium-based kagome metal, CsCr₃Sb₅, which is contrastingly featured with strong electron correlations, frustrated magnetism and characteristic flat bands close to the Fermi level. Under ambient pressure, this kagome metal undergoes a concurrent structural and magnetic phase transition at 55 K, with a stripe-like 4a₀ structural modulation. At high pressure, the phase transition evolves into two transitions, possibly associated with charge-density-wave and antiferromagnetic spin-density-wave orderings. These density-wave-like orders are gradually suppressed with pressure and, remarkably, a superconducting dome emerges at 3.65-8.0 GPa. The maximum of the superconducting transition temperature, T_c^max = 6.4 K, appears when the density-wave-like orders are completely suppressed at 4.2 GPa, and the normal state exhibits a non-Fermi-liquid behaviour, reminiscent of unconventional superconductivity and quantum criticality in iron-based superconductors^17,18. Our work offers an unprecedented platform for investigating superconductivity in correlated kagome systems.