Zeeman Effect On The Tunneling Spectra In The D-wave Superconductor Junctions And Josephson Current

The interplay between the superconductivity(SC) andferromagnetism(FM) has been a subject of extensive research formany years. Recently, the observation of the SC in ferromagneticmetals such as UGe₂, ZrZn₂, UrhGe and CeCoIn₅, has renewed theinterest on the ferromagnetic superconductors(FSs). It is shownthat a combination of ferromagnetic and superconductingproperties offers new possibilities in physics of Josephsonjunctions and their application based on the charge and spinsupercurrents.In this dissertation, we solve a self-consistent equation for thed-wave superconducting gap and the effective exchange field in themean-field approximation, study the Zeeman effects on the d-wavesuperconducting gap and thermodynamic potential. The Josephsoncurrents in the d-wave superconductor/insulating layer/d-wave Sjunction are calculated as a function of the temperature, exchangefield, and insulating barrier strength under a Zeeman magneticfield on the two d-wave Ss. It is found that the Josephson criticalcurrents in ferromagnetic d-wave S(FdS) junction depend on to agreat extent on the relative orientation of the effective exchangefield of the two S electrodes, and the crystal orientation of thed-wave S. The exchange field can under certain conditions enhancethe Josephson critical current in a FdS/I/FdS junction. Thepresence of an exchange field usually suppresses the Josephsoncritical current in FdS/FdS junction. The only exception that thecritical current increases with exchange field, the conditions areforα=0(αthe angle between the a axis of the d-wave S crystaland the interface normal), one needs low temperatures, stongbarrier strength, and an antiparallel configuration. In the caseofα≠0, however, the enhancement of Josephson critical current only on condition of weak barrier strength, low tempertures, andthe parallel configuration of the two FdS electrods.The dissertation is organized as follows. In Chapter 1, we givea brief outline of some fundamental concepts in the Andreevrefection, the Blonder-Tinkham-Klapwijk(BTK) theory and theJosephson effect. Some introductory materials on the FSs and thetriplet superconductors are presented in Chapter 2. In Chapter 3,we study the Zeeman effects on the d-wave superconducting gap andthermodynamic potential. In chapter 4, the Josepbson currentsin the d-wave superconductor/insulating layer/d-wave S junctionare calculated as a function of the temperature, exchange, field,and insulating barrier strength under a Zeeman magnetic field onthe two d-wave S.