Type-I superconductivity in KBi2 single crystals

We report on the detailed transport, magnetic, thermodynamic properties and theoretical calculation of KBi2 single crystals in superconducting and normal states. KBi2 exhibits metallic behavior at a normal state and enters the superconducting state below T-c = 3.573 K. Moreover, KBi2 exhibits low critical fields in all measurements, field-induced crossover from second- to first-order phase transition in specific heat measurements, the typical magnetization isotherms of type-I superconductors, and a small Ginzburg-Landau parameter k(GL) = 0.611. These results clearly indicate that KBi2 is a type-I superconductor with a thermodynamic critical field H-c = 234.3(3) Oe.