Anisotropy of the iron pnictide superconductor Ba(Fe1-xCox)2As2 (x=0.074, Tc=23 K)

Anisotropies of electrical resistivity, upper critical field, London penetration depth, and critical currents have been measured in single crystals of the optimally doped iron pnictide superconductor Ba(Fe1-xCox)(2)As-2 (x=0.074 and T-c similar to 23 K). The normal-state resistivity anisotropy was obtained by employing both the Montgomery technique and direct measurements on samples cut along principal crystallographic directions. The ratio gamma(rho)=rho(c)/rho(a) is about 4 +/- 1 just above T-c and becomes half of that at room temperature. The anisotropy of the upper critical field, gamma(H)=H-c2,H-ab/H-c2,H-c, as determined from specific-heat measurements close to T-c is in the range of 2.1-2.6, depending on the criterion used. A comparable low anisotropy of the London penetration depth, gamma(lambda)=lambda(c)/lambda(ab), was recorded from tunnel diode resonator measurements and found to persist deep into the superconducting state. An anisotropy of comparable magnitude was also found in the critical currents, gamma(j)=j(c,ab)/j(c,c), as determined from both direct transport measurements (similar to 1.5) and from the analysis of the magnetization data (similar to 3). Overall, our results show that iron pnictide superconductors manifest anisotropies consistent with essentially three-dimensional intermetallic compounds and bear little resemblance to cuprates.