Anisotropic superconducting properties of optimally doped ${\text{BaFe}}_2{\left({\text{As}}_{0.65}{\text{P}}_{0.35}\right)}_2$ under pressure

Magnetic measurements on optimally doped single crystals of ${\text{BaFe}}_2{\left({\text{As}}_{1-x}{\text{P}}_x\right)}_2$ $\left(x\approx 0.35\right)$ with magnetic fields applied along different crystallographic axes were performed under pressure, enabling the pressure evolution of coherence lengths and the anisotropy factor to be followed. Despite a decrease in the superconducting critical temperature, our studies reveal that the superconducting properties become more anisotropic under pressure. With appropriate scaling, we directly compare these properties with the values obtained for ${\text{BaFe}}_2{\left({\text{As}}_{1-x}{\text{P}}_x\right)}_2$ as a function of phosphorus content.

Figure 1

(Color online) Temperature dependence of the resonant frequency of the LCR circuit containing the sample in a microcoil [inset to (a)] at 21.5 kbar with magnetic field applied along (a) the $ab$ plane and (b) the $c$ axis of the crystal. The traces were offset to the normal state value of $\sim 12\text{MHz}$.

Figure 2

(Color online) Field dependence of $T_c$ for $H\parallel ab$ plane (closed symbols) and $H\parallel c$ axis (open symbols) at ambient pressure (circles), 9.4 kbar (squares) and 21.5 kbar (triangles).

Figure 3

(Color online) (a) Coherence lengths extracted from the dHvA data (Ref. 9) (circles) and $H_{c2}$ (squares). (b) Pressure dependence of $T_c$ measured using the anvil cell in the mutual inductance mode (closed squares) and the resonator mode (open squares). $T_c\left(x>0.35\right)$ (i.e., the overdoped part of the phase diagram) for ${\text{BaFe}}_2{\left({\text{As}}_{1-x}{\text{P}}_x\right)}_2$ (upper axis) is also shown for comparison. The inset to (b) shows examples of traces obtained using the mutual inductance mode. Using the scaling relation where 1% phosphorus corresponds to $\sim 2.4\text{kbar}$ (see text), the phosphorus content is represented in both panels by the upper axis.