title: Metal-insulator transition and orbital order in PbRuO3.
abstract: Anomalous low temperature electronic and structural behavior has been discovered in PbRuO3. The structure [space group Pnma, a=5.563 14(1), b=7.864 68(1), c=5.614 30(1) A] and metallic conductivity at 290 K are similar to those of SrRuO3 and other ruthenate perovskites, but a sharp metal-insulator transition at which the resistivity increases by 4 orders of magnitude is discovered at 90 K. This is accompanied by a first-order structural transition to an Imma phase [a=5.569 62(1), b=7.745 50(1), c=5.662 08(1) A at 25 K] that shows a coupling of Ru4+ 4d orbital order to distortions from Pb2+ 6s6p orbital hybridization. The Pnma to Imma transition is an unconventional reversal of the group-subgroup symmetry relationship. No long range magnetic order is evident down to 1.5 K. Calculations show that Pb 6s6p and Ru 4d orbital hybridization and strong spin-orbit coupling are significant.
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, 14109 Berlin, Germany.
authors.forename: Simon A J
authors.initials: SA
authors.lastname: Kimber
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Rodgers
authors.forename: Hua
authors.initials: H
authors.lastname: Wu
authors.forename: Claire A
authors.initials: CA
authors.lastname: Murray
authors.forename: Dimitri N
authors.initials: DN
authors.lastname: Argyriou
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Fitch
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Khomskii
authors.forename: J Paul
authors.initials: JP
authors.lastname: Attfield