Suppressed Superconductivity In Charge-Doped Li(Fe1-Xcox)As Single Crystals

Single crystals of the new unconventional superconductor LiFe1-xCox As with x = 0, 0.025, 0.05 were grown by a new approach using the self-flux technique. The superconducting transition temperature was found to decrease upon Co doping at the Fe site. Apparently, in LiFeAs this doping scheme suppresses superconductivity, in contrast to the effects of Co doping in other Fe-As compounds, where it suppresses the spin-density wave and establishes superconductivity. Angle-resolved photoemission spectroscopy shows that the bottom of electron-like bands sinks by about 17 meV upon 5% Co doping, which indicates that the chemical substitution of Co for Fe in LiFeAs results in charge doping.