Electronic phase diagram of the titanium oxypnictide superconductor BaTi2(Sb1–xBix)2O

Abstract

The titanium oxypnictide superconductor is studied by resistivity, magnetization and heat capacity measurements down to 0.5 K on the powder samples of all proportional solid solution BaTi2(Sb1–xBix)2O. An unusual electronic phase diagram as a function of x is obtained, in which a double superconducting dome with peaks at Tc = 3.6 and ~4 K appears across an intervening range with lower Tcs of ~1 K at 0.35 ≤ x ≤ 0.55. Moreover, a sudden jump in Tc is observed at xc between 0.55 and 0.60. These facts suggest unconventional mechanisms of the superconductivity of the titanium oxypnictides.