Three-dimensional nodal superconducting gap in single crystals Ba(Fe${}_{1-x}$Ni${}_x$)${}_2$As${}_2$

C. Martin, H. Kim, R. T. Gordon +6

The London penetration depth, $\lambda$, is directly related to the density, $n_s$, of the Cooper pairs (${\lambda }^2\propto 1/n_s$) and its variation with temperature provides valuable in…