Superconductivity arising from pressure-induced emergence of a Fermi surface in the kagome-lattice chalcogenide Rb2Pd3Se4

According to the Bardeen-Cooper-Schrieffer theory, superconductivity usually needs well-defined Fermi surface(s) with strong electron-phonon coupling and moderate quasiparticle density of states. A kagome lattice can host flat bands and topological Dirac bands; meanwhile, due to the parallel Fermi surfaces and saddle points, many interesting orders are expected. Here, we report the observation of superconductivity by pressurizing a kagome compound Rb2Pd3Se4 using a diamond-anvil-cell. The parent compound shows an insulating behavior; however, it gradually becomes metallic and turns to a superconducting state when high pressure is applied. High-pressure synchrotron measurements show that there is no structural transition occurring during this process. The density-functional-theory calculations illustrate that the insulating behavior of the parent phase is due to the crystalline field splitting of the partial Pd-4d t2g bands and the Se-derivative 4p band. However, the threshold of metallicity and superconductivity are reached when the Lifshitz transition occurs, leading to the emergence of a tiny Fermi surface at the I' point. Our results point to an unconventional superconductivity and shed light on understanding the electronic evolution of a kagome material.