Local characterization of superconductivity in BaFe2(As1-xPx)2

Abstract

We use magnetic force microscopy (MFM) to characterize superconductivity across the superconducting dome in ${\rm {BaFe}_2 \left(As_{1-x}P_x\right)_2}$, a pnictide with a peak in the penetration depth ($\lambda_{ab}$) at optimal doping ($\rm x_{opt}$), as shown in sample-wide measurements. Our local measurements show a peak at $\rm x_{opt}$ and a $T_C$ vs. $\lambda_{ab}^{-2}$ dependence similar on both sides of $\rm x_{opt}$. Near the underdoped edge of the dome $\lambda_{ab}$ increases sharply suggesting that superconductivity competes with another phase. Indeed MFM vortex imaging shows correlated defects parallel to twin boundaries only in underdoped samples and not for $\rm x\ge x_{opt}$.