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

Abstract

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

23 pages (11 main text, 12 support material)