Pressure effect on superconductivity of iron-based arsenic-oxide ReFeAsO0.85 (Re=Sm and Nd)

Here we report pressure effects on the superconducting transition temperature $(T_{{\rm c}})$ of the ReFeAsO0.85 (Re = Sm and Nd) system without fluorine doping. In situ measurements under high pressure showed that $T_{{\rm c}}$ of the two compounds decreases monotonously over the pressure range investigated. The pressure coefficients ${\rm d}T_{{\rm c}}/{\rm d}P$ in SmFeAsO0.85 and NdFeAsO0.85 were different, revealing the important influence of the deformation in layers on $T_{{\rm c}}$. Theoretical calculations suggested that the electron density of states decreases with increasing pressure, following the same trend of experimental data.