Superconductivity and normal state in-plane resistivity of electron-doped cuprates Nd-Ce-CuO: screened optical-phonon approach

Abstract

We have evolved an effective two-dimensional dynamic interaction, which embodies the screening of electrons by optical phonons and by plasmons to confer the attributes of the pairing mechanism leading to superconductivity in layered electron-doped cuprates. The electron-doped Nd-Ce-CuO cuprate behaves as an ionic solid containing isolated CuO2 layers of electrons as carriers, and a model dielectric function is set up that fulfils the appropriate sum rules on the electronic and ionic polarizabilities. Following strong coupling theory, the superconducting transition temperature of optimally-doped Nd-Ce-CuO is estimated as 28 K and the energy gap ratio is larger than the Bardeen-Cooper-Schrieffer value. The isotope effect exponent, coherence length and magnetic penetration depth are also estimated. Ziman's formula of resistivity is employed for analysis and a comparison is made with the temperature-dependent resistivity of a single crystal. The estimated phonon contribution together with the residual resistivity is lower than the reported data. The subtracted data infers a clear quadratic temperature dependence from Tc to near to room temperature. The implications of the model and its analysis are discussed.

Ramp-edge junctions between superconducting Nd1.85Ce0.15CuO4and La1.85Sr0.15CuO4

“…The final shape of the IV characteristic depends not only on barrier parameters U 1 , U 2 and L but also on the effective mass. The effective mass for NCCO and LSCO varies from 1 to m 5 e , where m e is the electron mass [30,31]. In the following we will only consider m m e = , to keep the model simple and to avoid additional fitting parameters.…”

Transition temperature and oxygen isotope effect of Nd doped cuprates: a three square well model

“…A pair of electrons may exchange a plasmon mode to achieve additional attraction and thereby yield high-T c values even if the electron phonon coupling part is weak or moderate. Both plasmons and optical phonons screen the gas of electron carriers which lie in the layered sequence of copper oxide planes and their Coulomb repulsion [14]. The evidence relating to the coupled phonon-electron excitations from Raman [7], infrared [8] and electron-tunnelling [9] spectroscopies associated with the oxygen in Nd-Ce-CuO, together with EELS [12] and reflectance [13] studies of Nd 1.85 Ce 0.15 CuO 4 , have provided the motivation for the present work.…”

At the interface between electron and hole-doped cuprates

“…The final shape of the IV characteristic depends not only on barrier parameters U 1 , U 2 and L but also on the effective mass. The effective mass for NCCO and LSCO varies from 1 − 5m e [127,128]. In the following we will only consider m = m e , to keep the model simple and to avoid additional fitting parameters.…”