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

TL;DR

This study uses magnetic force microscopy to locally analyze superconductivity in BaFe2(As1-xPx)2, revealing a peak in penetration depth at optimal doping and signs of competing phases near the underdoped edge.

Contribution

It provides the first local characterization of superconductivity across the doping phase diagram in BaFe2(As1-xPx)2, highlighting the spatial variation of superconducting properties and defect structures.

Findings

Peak in penetration depth at optimal doping

Sharp increase in penetration depth near underdoped edge

Correlation between defects and underdoped superconductivity

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 $\rm x\ge x_{opt}$.