Unconventional London penetration depth in Ba(Fe0.93Co0.07)2As2 single crystals

Gordon, R. T.; Ni, N.; Martin, C.; Tanatar, M. A.; Vannette, M. D.; Kim, H.; Samolyuk, G.; Schmalian, J.; Nandi, S.; Kreyssig, A.; Goldman, A. I.; Yan, J. Q.; Bud'ko, S. L.; Canfield, P. C.; Prozorov, R.

Unconventional London penetration depth in Ba(Fe0.93Co0.07)2As2 single crystals

Authors

Description

The London penetration depth, $λ(T)$, has been measured in several single crystals of Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$. Thermodynamic, electromagnetic, and structural characterization measurements confirm that these crystals are of excellent quality. The observed low temperature variation of $λ(T)$ follows a power-law, $Δλ(T) \sim T^n$ with $n=2.4 \pm 0.1$, indicating the existence of normal quasiparticles down to at least $0.02T_c$. This is in contrast to recent penetration depth measurements on single crystals of NdFeAsO$_{1-x}$F$_x$ and SmFeAsO$_{1-x}$F$_x$, which indicate an anisotropic but nodeless gap. We propose that a more three-dimensional character in the electronic structure of Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$ may lead to an anisotropic $s-$wave gap with point nodes that would explain the observed $λ(T)$.
4 pages