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Experiments in heavy-fermion metals and related theoretical work suggest that critical local-moment fluctuations can play an important role near a zero-temperature phase transition. We study such fluctuations at the quantum critical point of a Kondo impurity model in which the density of band states vanishes as /epsilon/(r) at the Fermi energy (epsilon=0).… (More)

We discuss non-Fermi liquid and quantum critical behavior in heavy fermion materials, focussing on the mechanism by which the electron mass appears to diverge at the quantum critical point. We ask whether the basic mechanism for the transformation involves electron diffraction off a quantum critical spin density wave, or whether a breakdown in the composite… (More)

Quantum phase transitions arise in many-body systems because of competing interactions that promote rivaling ground states. Recent years have seen the identification of continuous quantum phase transitions, or quantum critical points, in a host of antiferromagnetic heavy-fermion compounds. Studies of the interplay between the various effects have revealed… (More)

- Qimiao Si, J Lleweilun Smith
- 1996

We study the competition between intersite and local correlations in a spinless two-band extended Hubbard model by taking an alternative limit of infinite dimensions. We find that the intersite density fluctuations suppress the charge Kondo energy scale and lead to a Fermi liquid to non-Fermi liquid transition for repulsive on-site density-density… (More)

- J Lleweilun Smith, Qimiao Si
- 2000

We further develop an extended dynamical mean field approach introduced earlier. It goes beyond the standard D = ∞ dynamical mean field theory by incorporating quantum fluctuations associated with intersite (RKKY-like) interactions. This is achieved by scaling the intersite interactions to the same power in 1/D as that for the kinetic terms. In this… (More)

- Nabil Iqbal, Hong Liu, Márk Mezei, Qimiao Si
- 2010

Citation Iqbal, Nabil et al. " Quantum phase transitions in holographic models of magnetism and superconductors. " Physical Review D 82.4 (2010): 045002. Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article… (More)

We calculate the corrections to the conductivity and compressibility of a disordered metal when the mean free path is smaller than the screening length. Such a condition is shown to be realized for low densities and large disorder. Analysis of the stability of the metallic state reveals a transition to the insulating state in two-dimensions.

- Qimiao Si
- 1997

We study both the spin and electrical conductivities in models of relevance to the high T c cuprates. These models describe metallic states with or without spin-charge separation. We demonstrate that, given a linear in temperature dependence of the electrical resistivity, the spin resistivity should also be linear in temperature in the absence of… (More)

- Qimiao Si, Gabriel Kotliar
- 1993

We study an extended Hubbard model in the limit of infinite dimensions and its zero dimensional counterpart, a generalized asymmetric Anderson model. In the impurity model we find three kinds of mixed valence states: a) the usual strong coupling state in which a resonance forms at the Fermi level; b) a weak coupling state in which neither the impurity spin… (More)

- Xingye Lu, J T Park, Rui Zhang, Huiqian Luo, Andriy H Nevidomskyy, Qimiao Si +1 other
- Science
- 2014

Understanding the microscopic origins of electronic phases in high-transition temperature (high-T(c)) superconductors is important for elucidating the mechanism of superconductivity. In the paramagnetic tetragonal phase of BaFe(2-x)T(x)As2 (where T is Co or Ni) iron pnictides, an in-plane resistivity anisotropy has been observed. Here, we use inelastic… (More)