Normal-state resistivity and the depairing current density of BaFe₂(As,P)₂ nanobridges along the c axis

We report precise measurements to obtain the normal-state resistivity and the depairing current density of BaFe₂(As₁₋ₓPₓ)₂(x~0.29-0.32) nanobridges along the c axis, which are fabricated from single crystals near the optimal doping, by using focused ion beam (FIB) techniques. We obtained both of the $ab$-plane and c-axis resistivity (ρab and ρc) in the same part of a specimen, by fabricating the c-axis nanobridge in the middle of a narrow bridge extended in $ab$-plane, in spite of the slight deficiency of P dopant due to the additional FIB fabrication. The normal-state resistivity anisotropy agreed with the previous results for bulk samples, showing ρc/ρab < 8 just above the superconducting transition temperature, Tc, in the slightly underdoped region and a slight decrease with increasing temperatures. The critical current density obtained in the c-axis nanobridges near the optimal doping reaches ~8 MA/cm² at 0.15Tc, corresponding to about 87 % of a depairing limit derived by the Eilenberger equations. An extrapolation to $T=$0 K using the Ginzburg-Landau model suggests that the anisotropy of the depairing current density roughly corresponds to that of the normal-state resistivity. At low temperatures, we also observed a step-like voltage jump before arriving at the depairing limit, suggesting the occurrence of phase-slip phenomena near the depairing processes.