An intralayer pairing mechanism for the coexistence of charge- and spin-density waves induced superconductivity in LaSrCuO

Abstract

Starting from an effective two-dimensional dynamic interaction that includes screening of holes as carriers by charge density fluctuations and by optical phonons, we investigate the nature of a d-wave pairing mechanism leading to superconductivity in layered La-based cuprates. We consider the La–Sr–CuO system as an ionic solid containing layers of holes as carriers with a single CuO2 layer in a unit cell, where the localized spins form an antiferromagnetic (AF) order. The electron–phonon interaction matrix element in the case of an ordinary unit cell without the local AF order yields s-wave superconductivity. While for the unit cell with AF order, the wave-vector dependence of the intralayer effective interaction potential shows the sign reversal to create d-wave pairing due to localized antiferromagnetic spin order for the screened phonons. Following the strong coupling theory, the superconducting transition temperature, the isotope exponent, coherence length and magnetic penetration depth are also estimated. The implications of the intralayer pairing model and its analysis are discussed.

Interpretation of anomalous normal state optical conductivity of La–Sr–CuO cuprates

“…For a stack of 2D conducting planes well separated by an average spacing, d; the condition for optimised pairing infers that the 2D charge carrier density follows: n c d 2 ¼ 1 to obtain n c ø 2:3 £ 10 14 cm 22 : The other parameters of the carriers are the Fermi velocity v F ø 1:46 £ 10 7 cm s 21 and the Fermi energy e F ø 0:18 eV (1451 cm 21 ) [16]. Switching to the parameters related to ions, background dielectric constant 1 1 for hole doped cuprates is used as 4.5 [17].…”

“…There is a widespread opinion about the possibility of the main experimental results as La 1.85 Sr 0.15 CuO 4 to be described in the framework of the standard approach based on Fermi liquid ideas. Of course, one should take into account the effects of the coexistence of charge density fluctuations and the anti-ferromagnetic spin fluctuations in describing the attractive pairing force [16]. Optical conductivity sðvÞ measurements in mid-and near-IR regimes worked as powerful tool in yielding valuable information regarding the nature of low-lying charge excitations in metallic state.…”

Interpretation of optical conductivity in normal state of Iron-Based Superconductors CeOFeAs

“…in terms of memory functions [7] Γ µ (ω) and µ is either '0' or '1'. Furthermore, we denote Σ µ (0) = γ µ0 and Σ µ (∞) = γ µ∞ as the low and high frequency limits of the damping function of the quasi particles, respectively.…”

Effect of impurity scatterers on phonon, electron and magnon thermal transport in electron doped cuprate superconductors

“…The substitution of the trivalent rare-earth element Nd by tetravalent Ce introduces free carriers as electrons in each CuO 2 plane that are necessary to change Nd 2 CuO 4 into a superconducting compound. A first-principle calculation of the thermal conductivity in the normal and superconducting states requires a detailed knowledge of both electron and phonon bands as well the attractive pairing mechanism between a pair of carriers [4]. The particular system chosen for this study is ideal cuprate material in many ways.…”

“…While the spin fluctuation pairing mechanism leads naturally to an order parameter with d-wave pairing symmetry, the conventional Bardeen-Cooper-Schrieffer (BCS) electron phonon coupling pairing interaction yields s-wave superconductivity [1]. For the high-T c cuprate superconductors there is a very interesting large group activity for the pairing model [2][3][4] involving substances with phonons, polarons and bipolarons, excitons, charge density waves, spin density waves, magnetic excitations, and resonating bond state. Nevertheless, the BCS theory and the Cooper pairing concept remain the cornerstones of almost all current theories of superconductivity.…”