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

Abstract

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)2As2 (x=0.074 and Tc∼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 γρ=ρc/ρa is about 4±1 just above Tc and becomes half of that at room temperature. The anisotropy of the upper critical field, γH=Hc2,ab/Hc2,c, as determined from specific-heat measurements close to Tc is in the range of 2.1–2.6, depending on the criterion used. A comparable low anisotropy of the London penetration depth, γλ=λc/λab, 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, γj=jc,ab/jc,c, as determined from both direct transport measurements (∼1.5) and from the analysis of the magnetization data (∼3). Overall, our results show that iron pnictide superconductors manifest anisotropies consistent with essentially three-dimensional intermetallic compounds and bear little resemblance to cuprates.

Source-reported materials — not catalogue approval

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