Superconductivity in Cu Co-Doped Sr(x)Bi(2)Se(3) Single Crystals

In this study, we grew Cu co-doped single crystals of a topological superconductor candidate Sr [Formula: see text] Bi [Formula: see text] Se [Formula: see text] , and studied their structural and transport properties. We reveal that the addition of even as small an amount of Cu co-dopant as 0.6 atomic %, completely suppresses superconductivity in Sr [Formula: see text] Bi [Formula: see text] Se [Formula: see text]. Critical temperature (∼2.7 K) is rather robust with respect to co-doping. We show that Cu systematically increases the electron density and lattice parameters a and c. Our results demonstrate that superconductivity in Sr [Formula: see text] Bi [Formula: see text] Se [Formula: see text]-based materials is induced by significantly lower Sr doping level [Formula: see text] than commonly accepted [Formula: see text] , and it strongly depends on the specific arrangement of Sr atoms in the host matrix. The critical temperature in superconductive Sr-doped Bi [Formula: see text] Se [Formula: see text] is shown to be insensitive to carrier density.