The optical properties of the iron-chalcogenide superconductor K0.8Fe2−ySe2 with a critical temperature Tc = 31 K have been measured over a wide frequency range in the ab planes above and below Tc. The conductivity is incoherent at room temperature but becomes coherent (Drude-like) at T Tc; however, R 320 k , well above the threshold for the superconductor-insulator transition atR = h/4e2 6.9 k...

Abstract— The energy storage in an SMES is in the state of magnetic field within a superconductor coil. The magnetic field is formed by flowing DC current in the SMES. To ensure proper operation the temperature of SMES should be maintained below critical temperature. At this temperature the resistance of the coil is zero and hence there is no loss in stored energy. The ability of SMES to store ...