21,573 research outputs found

    Coherence scale of coupled Anderson impurities

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    For two coupled Anderson impurities, two energy scales are present to characterize the evolution from local moment state of the impurities to either of the inter-impurity singlet or the Kondo singlet ground states. The high energy scale is found to deviate from the single-ion Kondo temperature and rather scales as Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction when it becomes dominant. We find that the scaling behavior and the associated physical properties of this scale are consistent with those of a coherence scale defined in heavy fermion systems.Comment: 10 pages, 7 figures, extended versio

    Singularity in self-energy and composite fermion excitations of interacting electrons

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    We propose that a composite fermion operator fiΟƒ(2niΟƒΛ‰βˆ’1)f_{i\sigma}(2n_{i{\bar \sigma}}-1) could have coherent excitations, where fiΟƒf_{i\sigma} is the fermion operator for interacting electrons and niΟƒΛ‰n_{i{\bar \sigma}} is the number operator of the opposite spin. In the two-impurity Anderson model, it is found that the excitation of this composite fermion has a pseudogap in the Kondo regime, and has a finite spectral weight in the regime where the excitation of the regular fermion fiΟƒf_{i\sigma} has a pseudogap. In the latter regime, the self-energy of fiΟƒf_{i\sigma} is found to be singular near Fermi energy. We argue that this composite fermion could develop a Fermi surface with Fermi liquid behaviors but "hidden" from charge excitations in lattice generalizations. We further illustrate that this type of excitations is essential in addressing the pseudogap state and unconventional superconductivity.Comment: 10 pages, 6 figure
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