We investigate $\mathrm{Ba}({\mathrm{Fe}}_{0.65}{\mathrm{Ru}}_{0.35}{)}_2{\mathrm{As}}_2$, a compound in which superconductivity appears at the expense of magnetism, by transport measurements and angle resolved photoemission spectroscopy. By resolving the different Fermi surface pockets and deducing from their volumes the number of hole and electron carriers, we show that Ru induces neither hole nor electron doping. However, the Fermi surface pockets are about twice larger than in ${\mathrm{BaFe}}_2{\mathrm{As}}_2$. A change of sign of the Hall coefficient with decreasing temperature evidences the contribution of both carriers to the transport. Fermi velocities increase significantly with respect to ${\mathrm{BaFe}}_2{\mathrm{As}}_2$, suggesting a reduction of correlation effects.

• Received 25 February 2010

DOI:https://doi.org/10.1103/PhysRevLett.105.087001