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SUMMARY:Transport theory of pyrochlore conductors - Masafumi Udagawa\, Uni
 versity of Tokyo
DTSTART:20131212T141500Z
DTEND:20131212T151500Z
UID:TALK48288@talks.cam.ac.uk
CONTACT:Gareth Conduit
DESCRIPTION:Pyrochlore conductors Ln2Ir2O7 (Ln=rare earth) give valuable o
 pportunities to study the effect of geometrical frustration on itinerant e
 lectrons. These compounds have double-pyrochlore structure\, where Ln and 
 Ir ions are located on different pyrochlore sublattices interpenetrating w
 ith each other. The Ir 5d electrons form a conduction band\, while the Ln 
 4f electrons form localized moments\, i.e. these compounds can be consider
 ed as systems\, where itinerant electrons interact with localized moments 
 under strong geometrical frustration.\n\nIn this talk\, we focus on the co
 mpounds (Ln=Pr\, Nd)\, in which the Ln 4f localized moments develop substa
 ntial spin ice correlation\; an emergent magnetic state where most of the 
 tetrahedral units are occupied by “2-in 2-out” spin configuration. Ind
 eed\, the interplay between the conduction electrons and spin ice seems to
  explain anomalous transport phenomena observed in these compounds\, such 
 as non-monotonic magnetic field dependence of Hall conductivity [1] and lo
 w-temperature resistivity upturn [2].\n\nTo address these issues\, we adop
 t a spin-ice-type Ising Kondo lattice model on a pyrochlore lattice\, and 
 solve this model by applying the cluster dynamical mean-field theory and t
 he perturbation expansion in terms of the spin-electron coupling. As a res
 ult\, we found that (i) the resistivity shows a minimum at a characteristi
 c temperature below which spin ice correlation sets in [3]. Moreover\, (ii
 ) the non-monotonic Hall response can be understood as topological Hall ef
 fect due to the scattering from the spatially extended spin scalar chirali
 ty incorporated in spin ice manifold [4]. These results give unified under
 standing to the thermodynamic and transport properties of Ln2Ir2O7 (Ln=Pr\
 , Nd)\, and give new insights into the role of geometrical frustration in 
 itinerant systems.\n\nThis work has been done in collaboration with H. Ish
 izuka\, Y. Motome and R. Moessner.\n\n[1] Y. Machida et al.\, Phys. Rev. L
 ett. 98\, 057203 (2007).\n\n[2] S. Nakatsuji et al.\, Phys. Rev. Lett. 96\
 , 087204 (2006).\n\n[3] M. Udagawa\, H. Ishizuka and Y. Motome\, Phys. Rev
 . Lett. 108\, 066406 (2012).\n\n[4] M. Udagawa and R. Moessner\, Phys. Rev
 . Lett.\, 111\, 036602 (2013).
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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