Hole and electron contributions to the transport properties of Ba(Fe1-xRux)2As2 single crystals

We report a systematic study of structural and transport properties in single crystals of Ba(Fe1-xRux)(2)As-2 for x ranging from 0 to 0.5. The isovalent substitution of Fe by Ru leads to an increase in the a parameter and a decrease in the c parameter, resulting in a strong increase in the As-Fe-As angle and a decrease in the As height above the Fe planes. On Ru substitution, the magnetic order is progressively suppressed and superconductivity emerges for x >= 0.15 with an optimal T-c similar or equal to 20 K at x= 0.35 and coexistence of magnetism and superconductivity between these two Ru contents. Moreover, the Hall coefficient RH, which is always negative and decreases with temperature in BaFe2As2, is found to increase here with decreasing T and even changes sign for x >= 0.20. For x(Ru)= 0.35, photoemission studies have shown that the number of holes and electrons are similar with n(e)= n(h) similar or equal to 0.11 carriers/Fe, that is twice larger than found in BaFe2As2 [V. Brouet, F. Rullier-Albenque, M. Marsi, B. Mansart, J. Faure, L. Perfetti, A. Taleb-Ibrahimi, P. Le Fevre, F. Bertran, A. Forget, and D. Colson, arXiv:1002.4952 (unpublished)]. Using this estimate, we find that the transport properties of Ba(Fe0.65Ru0.35)(2)As-2 can be accounted for by the conventional multiband description for a compensated semimetal. In particular, our results show that the mobility of holes is strongly enhanced on Ru addition and overcomes that of electrons at low temperature when x(Ru) >= 0.15.