12 research outputs found
Approximation of excitonic absorption in disordered systems using a compositional component weighted CPA
Employing a recently developed technique of component weighted two particle
Green's functions in the CPA of a binary substitutional alloy we
extend the existing theory of excitons in such media using a contact potential
model for the interaction between electrons and holes to an approximation which
interpolates correctly between the limits of weak and strong disorder. With our
approach we are also able to treat the case where the contact interaction
between carriers varies between sites of different types, thus introducing
further disorder into the system. Based on this approach we study numerically
how the formation of exciton bound states changes as the strengths of the
contact potentials associated with either of the two site types are varied
through a large range of parameter values.Comment: 27 pages RevTeX (preprint format), 13 Postscript figure file
Colossal Magnetoresistance in a Mott Insulator via Magnetic Field Driven Insulator Metal Transition
We present a new type of colossal magnetoresistance CMR arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti doped Ca3Ru2O7. Such an insulator metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin lattice charge coupling. This study further provides a model approach to search for CMR systems other than manganites, such as Mott insulators in the vicinity of the boundary between competing phase