Enhancement of Tc by uniaxial lattice contraction in BiS2-based   superconductor PrO0.5F0.5BiS2
  We investigated the crystal structure and superconducting properties of As-grown and high-pressure-annealed PrO0.5F0.5BiS2. We found that the high-pressure annealing generates uniaxial lattice contraction along the c axis. Both As-grown and high-pressure-annealed PrO0.5F0.5BiS2 show bulk superconductivity. The Tc of PrO0.5F0.5BiS2 is clearly enhanced from Tczero = 3.6 K to Tczero = 5.5 K by high-pressure annealing. Unexpectedly, the semiconducting characteristics is relatively enhanced by high-pressure annealing. Namely, we assume that the enhancement of Tc can not be understood by an increase of electron carriers. Having considered these facts, we conclude that the enhancement of Tc correlates with uniaxial lattice contraction along the c axis in PrO0.5F0.5BiS2. 
Joe Kajitani, Keita Deguchi, Takafumi Hiroi, Atsushi Omachi, Satoshi   Demura, Yoshihiko Takano, Osuke Miura, Yoshikazu Mizu...
cond-mat.supr-con