Synthesis, structure and conductivity of sulfate and phosphate doped SrCoO3

The single-site two-electron exchange amplitude Jsd between the Cu 4s and Cu 3dx2−y2 states is found to be the pairing mechanism of high-Tc overdoped cuprates. The noninteracting part of the Hamiltonian spans the copper Cu 4s, Cu 3dx2−y2 and oxygen O 2px and O 2py states. Within the standard BCS treatment an explicit expression for the momentum dependence of the gap Δp is derived and shown to fit the angle-resolved photoemission spectroscopy data. The basic thermodynamic and electrodynamic properties of the model (specific heat C(T) and London penetration depth λ(T)) are analytically derived. These are directly applicable to cuprates without complicating structural accessories (chains, double CuO2 planes etc). We advocate that the pairing mechanism of overdoped and underdoped cuprates is the same, as Tc displays smooth doping dependence. Thus, a long-standing puzzle in physics is possibly solved.

https://itf.fys.kuleuven.be/~joi/papers/Superconductivity%20of%20overdoped%20cuprates%20the%20modern%20face%20of%20the%20ancestral%20two-electron%20exchange.pdf

Superconductivity of overdoped cuprates: the modern face of the ancestral two-electron exchange

Superconductivity in the system [Y0.8Ca0.2](SrBa) Cu3-x(BO3)xO7-δ with 0.1≤x≤0.5

The new YBa2Cu3-x(PO4)xO7-δ (x = 0; 0.03; 0.06; 0.09; 0.12) superconducting material was synthesized by the standard solid state reaction recipe. X-ray diffraction results show the effective substitution of copper for phosphate and also show no evidence of any impurity related with phosphate content. Resistivity, DC magnetization and heat capacity measurements reveal a superconducting transition for all samples with a maximum critical temperature up to 97 K, corresponding to the x = 0.03 sample. For higher doping values, the critical temperature decreases in an approximately linear response. In agreement with the charge transfer model, the critical temperature decreases with the carrier density. For x = 0.03, the critical temperature shows a rise up due to an approximation to the optimum density which separates over-doped and under-doped regimes. The maximum critical temperature achieved is one of the highest ever seen for the 123-type superconductors.

MAGNETIC, ELECTRIC AND EQUILIBRIUM PROPERTIES OF YBa2Cu3-x(PO4)xO7-δ HIGH TEMPERATURE SUPERCONDUCTING SYSTEM

We present X-ray and magnetization results for the compound [Y0.75Ca0.25]SrBaCu3−x(PO4)xOy with 0.0⩽x⩽0.30 synthesized at normal pressure and temperature. X-ray diffraction patterns show that for x= 0.0 the compound crystallizes into an orthorhombic phase. For increasing x a tetragonal phase is obtained. The Rietveld method was used to refine lattice constants. The magnetization measurements show that the samples were all superconductors over a range of temperatures from 10 to 100 K. The diamagnetic transition temperature Tc decreases with increasing (PO4)3− concentration (Tc=55 K for x=0.0 and Tc=35 K for x=0.30).

L.M. Dezanetie

Papers

Synthesis, structure and superconductivity of [Y0.75Ca0.25]SrBaCu3−x(PO4)xOy with 0.0⩽x⩽0.30