Pressure-induced superconductivity in lightly doped RFeAsO_1-xF_x (R=Sm and Nd)

Abstract

We performed the measurements of electrical resistivity (ρ) and dc magnetization (M) as a function of temperature (T) under pressure to investigate whether or not the superconductivity is induced by the application of pressure in lightly doped RFeAsO1-xFx (R=Sm and Nd) using pulse current sintered (PCS) high density polycrystalline specimens. We have successfully observed pressure induced superconductivity with T c of ∼6 K (∼8 K) above ∼4 GPa (∼1 GPa) for R=Sm (R=Nd). An anomaly corresponding to a magnetic phase transition into spin density wave (SDW) state was observed in the ρ(T) curves in the entire pressure range, indicating that the superconducting and SDW states coexist in the T-P phase diagram. Volume fraction of the superconductivity is found to be very small. This is consistent with the coexistence of the superconducting and SDW phases.