Multiband Responses in High-T c Cuprate Superconductors

Abstract

We report on the interplay of localized and extended degrees of freedom in the metallic state of high-temperature superconductors in a multiband setting. Various ways in which the bare magnetic response may become incommensurate are measured against both phenomenological and theoretical requirements. In particular, the pseudogap temperature is typically much higher than the incommensurability temperature. When microscopic strong-coupling effects with real-time dynamics between copper and oxygen sites are included, they tend to restore commensurability. Quantum transport equations for low-dimensional multiband electronic systems are used to explain the linear doping dependence of the dc conductivity and the doping and temperature dependence of the Hall number in the underdoped LSCO compounds. Coulomb effects of dopands are inferred from the doping evolution of the Hartree-Fock model parameters.

Evidence for a universal Fermi-liquid scattering rate throughout the phase diagram of the copper-oxide superconductors

“…It appears necessary to explicitly include the planar oxygen degrees of freedom. We note that calculations indicate that direct oxygen-oxygen propagation may generate arcs with sizeable oxygen spectral weight at the Fermi level [17,38]. Moreover, umklapp interactions might be essential to obtain the T 2 scattering rate [4,17,18].…”

“…A simple estimate of the carrier density from the arc length in the PG/FL regime indeed suggests that the density is low and increases with doping (≈p) [4]. More rigorous theoretical modeling yields the same conclusion [18,38]. The Hall data, including the present result, are overall consistent with a gradual evolution from p carriers that reside on arcs at temperatures below T ** toward a full Fermi surface of size 1+p not only at large doping levels [3], but also at high temperatures [5,39] (see also appendixes F and G).…”

“…As discussed in [25,38,80] and in the main text, with increasing doping the Fermi-surface topology of LSCO evolves from arcs to a diamond-like shape, and the Hall coefficient ceases to be a good measure of the carrier density. For LSCO, this becomes noticeable already for p = x > 0.08.…”

“…For LSCO, the observed deviation from n H =p/V, for p>0.08 and T c <T<T ** , and the apparent divergence of n H at p≈0.22 are related to changes in the curvature of the Fermi surface [25] (appendix D). The Hall coefficient therefore ceases to be a proper measure of the carrier density in this doping range, and the observed behavior is the result of the failure of the effective-mass approximation rather than of the applicability of the FL concept [38]. Indeed, for LSCO at p>0.08, cot(Θ H ) remains quadratic in temperature [5], but C 2 starts to increase (figure 3(b)) with the concomitant change in curvature of the underlying Fermi surface.…”

Effect of Substituting a Fraction of Cu by La on the Transport Properties of YBa&lt;sub&gt;2&lt;/sub&gt;(Cu&lt;sub&gt;1&amp;minus;x&lt;/sub&gt;La&lt;sub&gt;x&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;7&amp;minus;δ&lt;/sub&gt; Superconductor (0 ≤ x ≤ 0.06)

“…Results show that, basically, such doping can vary the hole concentration in a controlled manner influencing the superconducting properties of the material obtained [6]. Doping of different ions at the copper sites in (YBCO) superconductors serves as a useful diagnostic probe to investigate the role of different copper sites in the occurrence of superconductivity in these superconductors [7] [8]. In almost all such cases, the destabilization of (YBCO) superconducting phases and consequently the degradation of superconductivity in these compounds have been determined at low substitution level.…”