paper

Highly anisotropic energy gap in superconducting Ba(Fe $_{0.9}$ Co $_{0.1}$ ) $_{2}$ As $_{2}$ from optical conductivity measurements

arXiv:1005.0692 · doi:10.1103/PhysRevB.82.224507

Abstract

We have measured the complex dynamical conductivity, $I ¨ = I ¨ _{1} + i I ¨ _{2}$ , of superconducting Ba(Fe $_{0.9}$ Co $_{0.1}$ ) $_{2}$ As $_{2}$ ( $T_{c} = 22$ K) at terahertz frequencies and temperatures 2 - 30 K. In the frequency dependence of $I ¨ _{1}$ below $T_{c}$ , we observe clear signatures of the superconducting energy gap opening. The temperature dependence of $I ¨ _{1}$ demonstrates a pronounced coherence peak at frequencies below 15 cm $^{- 1}$ (1.8 meV). The temperature dependence of the penetration depth, calculated from $I ¨ _{2}$ , shows power-law behavior at the lowest temperatures. Analysis of the conductivity data with a two-gap model, gives the smaller isotropic s-wave gap of $I^_{A} = 3$ meV, while the larger gap is highly anisotropic with possible nodes and its rms amplitude is $I^_{0} = 8$ meV. Overall, our results are consistent with a two-band superconductor with an $s_{\pm}$ gap symmetry.

6 pages, 4 figures, discussion on pair-barking scattering and possible lifting of the nodes is added

Highly anisotropic energy gap in superconducting Ba(Fe0.9​Co0.1​)2​As2​ from optical conductivity measurements

Abstract

Highly anisotropic energy gap in superconducting Ba(Fe $_{0.9}$ Co $_{0.1}$ ) $_{2}$ As $_{2}$ from optical conductivity measurements