Microscopic theoretical study of the effect of SDW on oxypnictide super conductor

Abstract

The newly discovered iron-based superconductor provides a new class of superconducting system with second highest transition temperature as compared to that of the cuprate systems. It displays a complex interplay of magnetism, superconducting and lattice distortions in order to explain these phenomena in this system with different superconducting pairings. The present work reports different model Hamiltonians. The conduction electron Hamiltonian takes into account of the nearest-neighbor (NN) and next- nearest-neighbor (NNN) conduction electron hopping integrals. Similarly, the antiferromagnetic Hamiltonian describes the NN and NNN Heisenberg type spin-spin interactions within mean field approximation. The superconducting Hamiltonian takes into account of the BCS type interaction, taking into account of the s-wave, d-wave and s±-wave pairing symmetries. The total Hamiltonian is solved by Green s function technique and the parameters involved in the calculations are solved numerically and self-consistently. Besides introduction in chapter 1, the low energy spin density wave (SDW) phenomena are studied in chapter 2. The theory of Jahn-teller distortion describes lattice distortion in chapter 3. In chapter 4 describes the interplay of SDW and Jahn-teller effect in this system. Furthermore the chapter 5 describes the superconducting phenomena in the iron based system with different pairings. Importantly, the interplay of the superconductivity and the lattice distortion is discussed in chapter 6. The chapter 7 attempts to explain few phenomena of this system through a two band model. Finally the conclusion is given in chapter 8. The results and discussions are carried with reference to the experimental observations and the reports of the theoretical calculations.