Filamentary microstructure and linear temperature dependence of normal state transport in optimized high temperature superconductors

Abstract

A filamentary model of ''metallic'' conduction in layered high temperature superconductive cuprates explains the concurrence of normal state resistivities (Hall mobilities) linear in T (T ؊2 ) with optimized superconductivity. The model predicts the lowest temperature T 0 for which linearity holds and it also predicts the maximum superconductive transition temperature T c . The theory abandons the effective medium approximation that includes Fermi liquid as well as all other nonpercolative models in favor of countable smart basis states.For a long time it has been known (1) that in high temperature cuprate superconductors not only are the normal state resistivity and reciprocal Hall coefficient R H Ϫ1 anomalously linear in T, but also that this linearity is valid over the widest temperature range for exactly those compositions with the highest superconductive transition temperatures T c . Just as the isotope effect in simple metals provided the decisive clue that identified electron-phonon interactions as the attraction responsible for a condensed superconductive Fermion state, so this coincidence demonstrates that the microscopic mechanism responsible for high temperature superconductivity (HTSC) in layered cuprates involves peculiar non-Fermi liquid features of the normal state. Theorists interested in explaining the microscopic mechanism responsible for the high T c s of these materials could not ask for a more dramatic observation on which to base their analysis. Nevertheless, in spite of many efforts, no generally accepted explanation for either phenomenon is known, so that their concurrence with optimized superconductivity remains a mystery. The aim of the present paper is to show that a consistent model based on bridging interlayer impurities can be constructed that explains quantitatively not only this coincidence, but which also relates it to a microscopic model that explains a large number of very accurate measurements of density and temperature exponents of the metal-insulator transition (MIT) in the relatively simple case of semiconductor impurity bands where there is good reason to believe that the dopants are ideally (randomly) distributed. In this way the credentials of the cuprate impurity model are corroborated by independent simple impurity band data, which is very important because the structures of the cuprates are so complex. The ideas presented here for both problems are highly controversial and are far from being generally accepted, and the reasons for this will be discussed, as they are more important than the formal technical details of the calculations or the experiments. It should be remarked that the connection between the MIT and HTSC is not accidental, but is essential to the theory, and that there is a good deal of phenomenological evidence that supports such a relation in compositional trends of T c (2, 3). Linear Temperature Dependence of Normal-State TransportThe simplest explanation for the normal state linearity is that it arises solely from Fermi factors for a very na...

Charge-stripe ordering from local octahedral tilts: Underdoped and superconductingLa2−xSrxBožin1, Billinge2, Kwei3 et al. 1999Phys. Rev. B1165551View full textAdd to dashboardCite

“…[8][9][10] There is also growing circumstantial evidence that similar striped charge distributions are present more widely in other high-temperature superconducting cuprates, [11][12][13][14] and their possible importance in producing the hightemperature superconductivity itself is the subject of intensive investigation. [15][16][17][18][19][20] A number of recent reviews describe observations of lattice effects in the hightemperature superconductors in general. [21][22][23][24][25][26] However, there is currently no direct evidence that these stripe phases exist in superconducting samples, although there has been an observation where stripes and superconductivity were observed in the same samples.…”

QUANTUM PERCOLATION AND CHARGE TRANSPORT IN HIGH Tc SUPERCONDUCTORS

“…This model assumes as a basis that carriers are localized by disorder and that the phase diagram is the result of filamentary properties of localized states [8] and strong coulomb effects. Transport occurs through filamentary paths having maximum probability in the percolative network [8,9]. Superconductivity arises from a coupling of carriers with phonons within the localization length, a mechanism that enhances the electron-phonon couling to the values necessary to reach high J [10] .…”