Hydrostatic pressure study of the structural phase transitions and superconductivity in single crystals of (Ba1− x K x )Fe2As2 (x=0 and 0.45) and CaFe2As2

Abstract: We studied the effect of hydrostatic pressure (P) on the structural phase transitions and superconductivity in the ternary and pseudo-ternary iron arsenides CaFe2As2, BaFe2As2, and (Ba0.55K0.45)Fe2As2, by means of measurements of electrical resistivity (ρ) in the 1.8–300K temperature (T) range, pressures up to 20kbar, and magnetic fields up to 9T. CaFe2As2 and BaFe2As2 (lightly doped with Sn) display structural phase transitions near 170 and 85K, respectively, and do not exhibit superconductivity in ambient pressure, while K-doped (Ba0.55K0.45)Fe2As2 is superconducting for T<30K. The effect of pressure on BaFe2As2 is to shift the onset of the crystallographic transformation down in temperature at the rate of ~−1.04K/kbar, while shifting the whole ρ(T) curves downward, whereas its effect on superconducting (Ba0.55K0.45)Fe2As2 is to shift the onset of superconductivity to lower temperatures at the rate of ~−0.21K/kbar. The effect of pressure on CaFe2As2 is first to suppress the crystallographic transformation and induce superconductivity with onset near 12K very rapidly, i.e., for P<5kbar. However, higher pressures bring about another phase transformation characterized by reduced-resistivity, and the suppression of superconductivity, confining superconductivity to a narrow pressure dome centered near 5kbar. Upper critical field (H c2) data in (Ba0.55K0.45)Fe2As2 and CaFe2As2 are discussed. [Copyright &y& Elsevier]