arXiv subjects

E. Miranda

Publications and source records attributed to E. Miranda.

62 records · Page 4Linked to original sources

arXiv1997

Scaling theory of two-dimensional metal-insulator transitions

We discuss the recently discovered two-dimensional metal-insulator transition in zero magnetic field in the light of the scaling theory of localization. We demonstrate that the observed symmetry relating conductivity and resistivity follows directly from the quantum critical behavior associated with such a transition. In addition, we show that very general scaling considerations imply that any disordered two dimensional metal is a perfect metal, but most likely not a Fermi liquid.

cond-mat.dis-nn↗

arXiv1996

Kondo disorder: a possible route towards non-Fermi liquid behavior

We present a general model of disorder in Kondo alloys that, under certain conditions, leads to non-Fermi liquid behavior. The central underlying idea is the presence of a distribution of local Kondo temperature scales. If this distribution is broad enough, such that there are sites with arbitrarily low Kondo temperatures, a non-Fermi liquid phase is formed. We analyze thermodynamics and transport in this approach and show it is consistent with a number of Kondo alloys. We also compare the predictions of this model with the measured dynamical magnetic response of these systems.

cond-mat.str-el↗

arXiv1996

Disorder-driven non-Fermi liquid behavior in Kondo alloys

We demonstrate that a model of disordered Anderson lattices can account for many non-Fermi liquid features observed in a number of Kondo alloys. Due to the exponential nature of the Kondo temperature scale, even moderate disorder leads to a rather broad distribution of Kondo temperatures, inducing strong effective disorder seen by the conduction electrons. Spins with very small Kondo temperatures remain unquenched and dominate the low temperature properties. The model predicts logarithmic divergences in thermodynamic quantities at low temperatures. We also find a linear temperature dependence of the resistivity, a feature that remained a stumbling block in previous theoretical attempts. We argue that for realistic amounts of disorder, such marginal Fermi liquid behavior is a very robust feature of disordered Kondo alloys.

cond-mat↗

arXiv1994

Possible Relevance of Odd Frequency Pairing to Heavy Fermion Superconductivity

What is the character of the gapless quasiparticles in heavy fermion superconductors (HFSC)? We discuss an odd-frequency pairing interpretation of HFSC which leads to a two component model for the quasiparticle excitations. In this picture, line zeroes of unpaired electrons may coexist with gapless surfaces of paired electrons, with vanishing spin and charge coherence factors.

cond-mat↗

arXiv1994

Three Body bound-states and the development of odd frequency pairing

We propose that the development of odd-frequency superconductivity is driven by the collective formation of neutral three body bound-states. Using a three-body bound-state ansatz we develop a mean-field theory for odd-frequency pairing within the Kondo Lattice model. Three body bound-state formation leads to the formation of a gapless band of fermions with a neutral, spinless Fermi surface. We discuss the low energy excitations of these modes, suggesting them as a possible explanation for the absence of anisotropy in the thermal conductivity of heavy fermion superconductors.

cond-mat↗

arXiv1993

Instabilities of the Abrikosov-Suhl resonance

We consider the possibility that instabilities of the Abrikosov-Suhl resonance lead to new fixed point behavior of the Kondo effect in a lattice environment. In one scenario, a pairing component to the resonant scattering develops in the Kondo lattice, leading to an odd frequency superconductor. We discuss experiments that can discriminate between this picture and d-wave pairing, and its relationship to the non Fermi liquid fixed point of the overscreened Kondo model.

cond-mat↗

arXiv1993

Odd Frequency Pairing in the Kondo Lattice

We discuss the possibility that heavy fermion superconductors involve odd-frequency pairing of the kind first considered by Berezinskii. Using a toy model for odd frequency triplet pairing in the Kondo lattice we are able to examine key properties of this new type of paired state. To make progress treating the strong $n_f=1$ constraint in the Kondo lattice model we use the technical trick of a Majorana representation of the local moments, which permits variational treatments of the model without a Gutzwiller approximation. The simplest mean field theory involves the development of bound states between the local moments and conduction electrons, characterized by a spinor order parameter. We show that this state is a stable realization of odd frequency triplet superconductivity with surfaces of gapless excitations whose spin and charge coherence factors vanish linearly in the quasiparticle energy. A $T^3$ NMR relaxation rate coexists with a linear specific heat. We discuss possible extensions of our toy model to describe heavy fermion superconductivity.

cond-mat↗

arXiv1993

Possible Realization of Odd Frequency Pairing in Heavy Fermion Compounds

Using Majorana Fermions to represent spins we re-examine the Kondo Lattice model for heavy fermions. The simplest decoupling procedure provides a realization of odd frequency superconductivity, with resonant pairing and surfaces of gap zeros. Spin and charge coherence factors vanish linearly with the energy on the Fermi surface, predicting a linear specific heat, but a $T^3$ NMR relaxation rate. Possible application to heavy fermions is suggested.

cond-mat↗