A New Superconductor with Ir Kagome Lattice

Novel materials consisting of Kagome lattice are recently strongly desired and thought to host exotic quantum physics such as quantum spin liquid state, topological quantum state and superconductivity. Flat bands, Dirac cones and topologically nontrivial surface states are also supposed to be favored in Kagome compounds. Here in this work, we present the synthesis and characterization of a new layered ternary material with heavy-metal Kagome lattice. Small crystals can be found in as-cast samples after arc melting. Physical properties measurements performed on the crystals show bulk superconducting behavior with T_c ~ 5.2 K. The magnetization results indicate a small lower critical field ~ 5.5 mT while the upper critical field ~ 4.7 T is determined by electrical resistivity measurements. The normalized superconducting heat capacity jump is calculated to be 2.45, which significantly exceeds the value for weak coupling BCS superconductor (1.43), suggesting strongly coupled nature in the new material. Moreover, the short Ginzburg-Landau coherence length implies strong electron-electron correlation in our material. Electronic structures were calculated with and without consideration of spin-orbit coupling (SOC) effect to further interpret the physical properties. Semimetallic behavior is suggested by band structure calculated with SOC effect. The d states of heavy atoms were found to be dominant near the Fermi energy (E_F) while a nearly flat band was observed around 100 meV below E_F as well. Two Dirac points found close to E_F without consideration of SOC effect suggest potentially topological interests in the newly discovered system.