Heat transport in RbFe2As2 single crystal: evidence for nodal   superconducting gap
  The in-plane thermal conductivity of iron-based superconductor RbFe$_2$As$_2$ single crystal ($T_c \approx$ 2.1 K) was measured down to 100 mK. In zero field, the observation of a significant residual linear term $\kappa_0/T$ = 0.65 mW K$^{-2}$ cm$^{-1}$ provides clear evidence for nodal superdonducting gap. The field dependence of $\kappa_0/T$ is similar to that of its sister compound CsFe$_2$As$_2$ with comparable residual resistivity $\rho_0$, and lies between the dirty and clean KFe$_2$As$_2$. These results suggest that the (K,Rb,Cs)Fe$_2$As$_2$ serial superconductors have a common nodal gap structure. 
Z. Zhang, A. F. Wang, X. C. Hong, J. Zhang, B. Y. Pan, J. Pan, Y. Xu,   X. G. Luo, X. H. Chen, S. Y. Li
cond-mat.supr-con cond-mat.str-el