Condensed Matter Physics Seminar

LiV204: A frustration induced heavy fermion metal

Dr. John Hopkinson
Dept of Physics, U. of Toronto

Time
Wed. October 20, 2004     10:30 AM     Stirling 501

Abstract

How does the interplay of mixed valence and geometric frustration result in a heavy fermion state for LiV2O4?. I will briefly review the experimental evidence for the heavy fermion state realized in this compound in contrast to that seen in isostructural ZnV204 (an S=1 Mott insulator) and LiTi2O4 (a BCS superconductor). Unlike in conventional heavy fermions, 'conduction electrons' and 'localized electrons' here both originate from the d-electrons of the magnetic sites, leading to unusual properties of the resistivity at high temperatures as the 'conduction electrons' begin to localize. Within our proposed two-stage spin-quenching scenario, local valence flucutations are responsible for the formation of partially quenched, spin-1/2 moments below room temperature. Frustration of the intersite spin couplings then drives the system to realize the heavy Fermi liquid seen at low temperatures, providing a natural explanation for the sign change of the Hall coefficient along the way. A simplified square lattice version will be presented for illustration. A unique symmetry is predicted for the pyrochlore solution which has implications for the nature of the heavy quasiparticles observed.

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