C. T. Wolowiec, B. D. White, I. Jeon, D. Yazici, K. Huang, M. B. Maple
Measurements of electrical resistivity were performed as a function of temperature between 3 and 300 K at various pressures up to 2.8 GPa on the LnO0.5F0.5BiS2 (Ln = Pr, Nd) compounds. At low pressure, PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2 exhibit superconductivity with Tc of 3.5 and 3.9 K, respectively. Both compounds display semiconducting behavior at low pressure in the normal state which is strongly suppressed with pressure. Both compounds undergo a pressure-induced transition from a low Tc superconducting phase to a high Tc superconducting phase in which Tc reaches 7.6 and 6.4 K for PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2, respectively. The pressure-induced transition is characterized by a rapid increase in Tc within a small pressure range of ~0.3 GPa for both compounds. For PrO0.5F0.5BiS2, the transition pressure correlates with the pressure where the rate of suppression of semiconducting behavior in the normal state saturates. For NdO0.5F0.5BiS2, the transition pressure between superconducting phases corresponds to the pressure that induces a semiconductor-metal transition in the normal state. The suppression of semiconducting behavior and evolution of Tc with pressure in the compounds LnO0.5F0.5BiS2 (Ln = Pr, Nd) is markedly similar to behavior recently reported for the BiS2-based compounds LnO0.5F0.5BiS2 (Ln = La, Ce). [arXiv 1307.4157 (2013), Phys. Rev. B accepted] A plot of the transition pressure versus lanthanide element (Ln = La, Ce, Pr, Nd) indicates that there is an increase in the value of transition pressure with decrease in atomic radius of the lanthanide element in LnO0.5F0.5BiS2. In addition, the "jump" in Tc between the two superconducting phases becomes smaller with decrease in atomic radius of lanthanide element (Ln = La, Ce, Pr, Nd). We suspect that this behavior is a general characteristic of the BiS2-based family of layered superconductors LnO0.5F0.5BiS2.
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http://arxiv.org/abs/1308.1072
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