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 ( and ). 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 is about just above and becomes half of that at room temperature. The anisotropy of the upper critical field, , as determined from specific-heat measurements close to is in the range of 2.1–2.6, depending on the criterion used. A comparable low anisotropy of the London penetration depth, , 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, , as determined from both direct transport measurements and from the analysis of the magnetization data . Overall, our results show that iron pnictide superconductors manifest anisotropies consistent with essentially three-dimensional intermetallic compounds and bear little resemblance to cuprates.
8 More- Received 6 January 2009
DOI:https://doi.org/10.1103/PhysRevB.79.094507
©2009 American Physical Society