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

We use magnetic force microscopy (MFM) to characterize superconductivity across the superconducting dome in ${\mathrm{B}\mathrm{a}\mathrm{F}\mathrm{e}}_2{\left(\mathrm{A}{\mathrm{s}}_{1-\mathrm{x}}{\mathrm{P}}_{\mathrm{x}}\right)}_2$, a pnictide with a peak in the penetration depth (${\lambda }_{ab}$) at optimal doping (${\mathrm{x}}_{\mathrm{o}\mathrm{p}\mathrm{t}}$), as shown in sample-wide measurements. Our local measurements show a peak at ${\mathrm{x}}_{\mathrm{o}\mathrm{p}\mathrm{t}}$ and a $T_C$ vs. ${\lambda }_{ab}^{-2}$ dependence similar on both sides of ${\mathrm{x}}_{\mathrm{o}\mathrm{p}\mathrm{t}}$. 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 $\rm x\ge x_{opt}$.