Pseudoisotropic upper critical field in cobalt-doped SrFe2As2 epitaxial films

• Published in: Physical review letters Vol. 102; no. 11; p. 117004
• Main Authors: Baily, S A, Kohama, Y, Hiramatsu, H, Maiorov, B, Balakirev, F F, Hirano, M, Hosono, H
• Format: Journal Article
• Language: English
• Published: United States 20-03-2009
• ISSN: 0031-9007
• DOI: 10.1103/PhysRevLett.102.117004

We present resistivity measurements of the complete superconducting upper critical field (H{c2}) phase diagram as a function of angle (theta) and temperature (T) for cobalt-doped SrFe2As2 epitaxial films to 0.5 K and 50 T. Although H{c2}(theta) at 10 K is indistinguishable from that derived from a single-band anisotropy model, the apparent anisotropy H{c2}{ perpendicularc}/H{c2};{ parallelc} linearly decreases to 1 at low T, with H{c2}(0)=47 T. The data are well described by a two-band model with small, opposing anisotropies for the bands. This unusual relationship is confirmed by the observation of a local maximum for H{c2};{ parallelc} at low T.