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Chinese Journal of Physics

The Effect of Non-Magnetic Disorder on a D-Wave Superconductor in the Presence of a Van Hove Singularity

Grzegorz Litak A

Published Feb 1, 2006• 0 citations
OpenAlex

Abstract

We apply the Coherent Potential Approximation (CPA) to an extended Hubbard model to describe disordered superconductors with d-wave pairing. We discuss the pair-breaking effect caused by non-magnetic disorder in the presence of a Van Hove singularity. It is shown that singularities soften the suppression of a superconducting critical temperature.

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van Hove Singularity effects in Strongly Correlated Fermions

Pinaki Majumdar, H. R. Krishnamurthy

We examine the effects of a van Hove singularity (vHs) in the density of states (DOS) of a two dimensional, $t-t'-U$ Hubbard model within the local approximation. Within our approximation the non-interacting Fermi surface is always retained away from half-filling; and we find that the vHs in the DOS survives, and for hole doping is nearly "pinned" to the Fermi level due to the enhancement of the effective mass, $m^*$. We discuss the electron-hole asymmetry of this phenomena and its relevance to the electron and hole doped cuprates. At optimal (hole) doping, with the Fermi level at the vHs, we find that the single particle damping rate $Γ$, and the resistivity $ρ_{dc}$, scale as $T$ for moderately low temperatures ($T \gtrsim 100$K), while for the electron doped system $Γ$ and $ρ_{dc} \sim T^2$.

arXiv:cond-mat/9604057•Apr 10, 1996•0 citations
We apply the Coherent Potential Approximation (CPA) to an extended Hubbard model to describe disordered superconductors with d-wave pairing. We discuss the pair-breaking effect caused by non-magnetic disorder in the presence of a Van Hove singularity. It is shown that singularities soften the suppression of a superconducting critical temperature.
The $t\ensuremath{-}{t}^{\ensuremath{'}}$ Hubbard model for the Fermi level near the van Hove singularity is considered within the renormalization group and parquet approaches. Interplay of ferromagnetic, antiferromagnetic, and superconducting channels is investigated, and the phase diagram of the model is constructed. In comparison with previous approaches, the account of ferromagnetic fluctuations suppresses superconducting pairing and, vice versa, the influence of the Cooper channel decreases the Curie temperature, so that the Stoner criterion is inapplicable even qualitatively.
We devise a computational approach to the Hubbard model that captures the strong coupling dynamics arising when the Fermi level is at a Van Hove singularity in the density of states. We rely on an approximate degeneracy among the many-body states accounting for the main instabilities of the system (antiferromagnetism, d-wave superconductivity). The Fermi line turns out to be deformed in a manner consistent with the pinning of the Fermi level to the Van Hove singularity. For a doping rate $\ensuremath{\delta}\ensuremath{\sim}0.2,$ the ground state is characterized by d-wave symmetry, quasiparticles gapped only at the saddle points of the band, and a large peak at zero momentum in the d-wave pairing correlations.
An interplay between the superconductivity and spin density wave (SDW) is studied from the perturbative point of view based on the two dimensional Hubbard model. It is shown that the d-pairing superconductivity is induced by spin fluctuations near the SDW boundary. The superconducting transition temperature ( T c ) is found to be remarkably suppressed by the renormalization through the electron self-energy, and to be sensitive to the band parameters due to nesting of the Fermi surface and the presence of the van Hove singularity as well as to the Fermi energy and the on-site interaction. As a consequence T c is enhanced by the next-nearest-neighbour hopping integral. The relation between the present result and experiments of high T c superconductors is discussed.
We examine the effects of a van Hove singularity (vHs) in the density of states (DOS) of a two dimensional, t−t′−Ut-t'-Ut−t′−U Hubbard model within the local approximation. Within our approximation the non-interacting Fermi surface is always retained away from half-filling; and we find that the vHs in the DOS survives, and for hole doping is nearly "pinned" to the Fermi level due to the enhancement of the effective mass, m∗m^*m∗. We discuss the electron-hole asymmetry of this phenomena and its relevance to the electron and hole doped cuprates. At optimal (hole) doping, with the Fermi level at the vHs, we find that the single particle damping rate ΓΓΓ, and the resistivity ρdcρ_{dc}ρdc​, scale as TTT for moderately low temperatures (T≳100T \gtrsim 100T≳100K), while for the electron doped system ΓΓΓ and ρdc∼T2ρ_{dc} \sim T^2ρdc​∼T2.