Coexistence of Dirac-Cone States and Superconductivity in Iron Pnictide Ba(Fe${}_{1-x}$Ru${}_x$As)${}_2$

The Ru doping effect on the Dirac cone states is investigated in iron pnictide superconductors Ba(Fe${}_{1-x}$Ru${}_x$As)${}_2$ using the transverse magnetoresistance (MR) measurements as a function of temperature. The linear development of MR against magnetic field $B$ is observed for $x$ = 0 - 0.244 at low temperatures below the antiferromagnetic transition. The $B$-linear MR is interpreted in terms of the quantum limit of the Dirac cone states by using the model proposed by Abrikosov. An intriguing evidence is shown that the Dirac cone state persists on the electronic phase diagram where the antiferromagnetism and the superconductivity coexist.