COMPETING QUANTUM ORDERINGS IN CUPRATE SUPERCONDUCTORS: A MINIMAL MODEL

We present a minimal model for cuprate superconductors. At the unrestricted mean-field level, the model produces homogeneous superconductivity at large doping, striped superconductivity in the underdoped regime and various antiferromagnetic phases at low doping and for high temperatures. On the underdoped side, the superconductor is intrinsically inhomogeneous and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. The model is applied to calculate experimentally measurable ARPES spectra.

SUPERCONDUCTIVITY IN CUPRATES, THE VAN HOVE SCENARIO

The existence of van Hove singularities close to the Fermi level in all high T c cuprates has been experimentally established. We develop a theory using these singularities which enables us to compute the main physical properties: T c gap and gap anisotropy, specific heat and magnetic susceptibility. All these results agree well with the experimental data in the optimal and overdoped regime. In the underdoped regime, we use the theory of electron-electron interaction in disordered conductors to explain the pseudo-gap behaviour.

INVESTIGATION ON SYNTHESIS AND CHARACTERIZATION OF Hg1−xTlxBa2Ca2Cu3O8+δ WITH 0.2≤x≤0.8

In the present investigation, Tl substituted Hg bearing cuprate high temperature superconductors corresponding to Hg 1−x Tl x Ba 2 Ca 2 Cu 3 O 8+δ with x=0.2, 0.4, 0.5, 0.6, 0.7 and 0.8, have been synthesized. The as synthesized phases characterized through XRD and TEM have been found to possess Hg:1223 as the dominant structural phase. These superconductors, with increasing Tl concentration have been found to pass from the underdoped through optimally doped to the overdoped regimes. The Tc for the underdoped regime (x=0.2) corresponds to ~117 K, for the overdoped regime (x=0.8), it is ~119 K. An interesting result emanating from the present study relates to the fact that an optimum Tc of ~122 K is obtained through oxygenation (annealing in oxygen) of the underdoped regime, reduction (annealing in Ar+H2) of overdoped regime, or else through optimum hole doping by suitable adjustment of substituted Tl concentration (x=0.6).