Effect of pressure on a "111"-type iron pnictide superconductor

The behavior of superconductivity of “111”-type iron pnictide superconductors, namely, LiFeAs, NaFeAs and LiFeP, is investigated at different pressures through electrical resistance measurements. For LiFeAs and LiFeP, the superconducting transition temperature T c decreases monotonously with increasing pressure, with the pressure coefficient of dT c /dP being−1.38 and−1.26 K/GPa, respectively. The T c of NaFeAs increases to a maximum value with the pressure increasing to 3 GPa; further increasing the pressure suppresses T c with the slope of dT c /dP about−3.40 K/GPa.