1993

Ph.D

University of Madras

A theoretical study of the interlayer pair hopping mechanism of high temperature superconductivity is undertaken in this thesis. The assumptions such as " i) the low energy excitations in the normal state are spin-charge decoupled and ii) the conducting state above Tc is two dimensional", are considered for the argument of reconcilation of few well known experimental facts with these assumptions. Some basic notions of RVB theory are reviewed; 'Simple microscopic derivation of the effective hamiltonian describing pair hopping' is presented; This study examines how a system of noninteracting spinons and holons responds to a weak interlayer coupling t1, and shows that physical processes involving holon pair hopping (between the coupled layers) are generated. The limitations of working with the effective hamiltonian for the holons are discussed, and a model hamiltonian for pair hopping is presented and a gap equation which is different from the BCS equation is also obtained. The momentum and temperature dependence of the gap is studied in detail. Josephson current between two superconductors is calculated. The results of this study demonstrates the importance of strong correlation vis a vis pair hopping. A single electron hopping acting as a pair breaking mechanism is discussed and its effect on the superconducting gap is examined.