Local Quantum Criticality in an Iron-Pnictide Tetrahedron
ORAL
Abstract
The iron-based superconductors display a close experimental relationship between the Tc values and the tetrahedral bond angle of the As-Fe-As layer, with optimal Tc clustering close to the ideal tetrahedron geometry. This motivates a study of the local physics of an Fe atom within an As tetrahedron, and we find a strong interplay between spin and orbital degrees of freedom. The d-orbitals are crystal field split, and the lower eg orbitals have an SU(2) $\times$ SU(2) symmetry with both a spin and orbital Kondo interaction. The spin Kondo coupling is strongly reduced by the Hund's coupling; hence the system flows to an over-screened orbital Kondo state. A perturbative RG analysis of the strong-coupling fixed point is done using a Majorana fermion representation of the SU(2) $\times$ SU(2) symmetry. The low-temperature physics, and the possibility of a Marginal Fermi Liquid ground state, is carefully studied using the CTQMC method, taking into account the effect of Hund's coupling on the Kondo physics.
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Authors
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T. Tzen Ong
Department of Physics \& Astronomy, Rutgers University, Center for Materials Theory, Physics and Astronomy, Rutgers University
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Patrick Semon
Department of Physics, University of Sherbrooke
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A.-M.S. Tremblay
Department of Physics, University of Sherbrooke, Universite de Sherbrooke, Quebec, Canada, and Canadian Institute for Advanced Research, Universite de Sherbrooke, Universite de Sherbrooke, Quebec, Canada and CIFAR, Canada
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Piers Coleman
Rutgers University, Center for Materials Theory Department of Physics \& Astronomy, Rutgers University, Center for Materials Theory, Rutgers University, Piscataway, NJ 08854, USA, Center for Materials Theory, Physics and Astronomy, Rutgers University