High-Temperature Superconductivity and Lattice Relaxation in Lithium-Deposited FeSe on SrTiO sub( 3)

We studied the effect of strain, interface, and electron doping on the superconductivity in thin FeSe film on SrTiO sub( 3) by angle-resolved photoemission spectroscopy (ARPES). We observed the superconductivity with T sub( c) as high as 43 K in a lithium (Li) deposited heavily electron-doped multilayer FeSe film. We found a significant relaxation of tensile strain at the surface in contrast to the case of potassium (K) deposition, although the high-T sub( c) superconductivity is commonly observed in both cases. We discuss the interplay among carrier doping, tensile strain, and high-T sub( c) superconductivity by comparing ARPES results on Li- and K-deposited FeSe films.