More recently STM experimets present firm evidence of some kind of charge
modulation in underdoped cuprates. The peculiar observations of the above
experiments are located in the so called pseudo-gap region of the phase
diagram, just over the superconducting-dome. The model that will be used
captures in a simple way the idea that the pseudo-gap phase is formed of bound
fermion pairs which are close to a CDW instability but generally do not have
long range order due to quenched disorder. Thus the charge degrees of freedom
will be modeled by an Ising order parameter in the presence of quenched
disorder, so representing a charge glassy phase. This glassy phase will be in
competition with a superconducting phase modeled by a complex order parameter.
As a first step we will study the model in one dimension without disorder to
familiarize with it and also to search for a possible explanation of the Giant
Proximity Effect (GPE). After that we will investigate numerically the ground
state properties of the 2-dimensional lattice model, focusing our attention
especially on the stiffness and magnetization of the system in the xy plane. We
will show that disorder can induce superconductivity in a CDW phase. This
picture is really interesting because it could show how an insulating system
can produce a superconducting phase thank to the interplay with impurites.Comment: 162 pages, PhD thesi
