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Study Quantum Phases of Superconducting Kondo Lattice Model In s and p wave symmetry of Gap Function

Moghtader, Mohammad Reza | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55968 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Kargarian, Mehdi
  7. Abstract:
  8. In this thesis, first we study superconductivity and its mechanisms then classify different types of that based on symmetry of gap function. After that, we shall discuss metallic systems that have impurities in them and propose two successful model describing this phenomenon, Anderson’s model and Kondo’s model. In the next step, by introducing Kondo lattice model which is an ordered array of impurities in system, try to solve it by mean-field approximation and will be seen a phase transition in a characteristic temperature known as Kondo’s temperature. Then generalize these models to situation when background system is a superconductor and study it’s behavior and quantum phases. Although Anderson showed that a conventional BCS superconductor is robust with respect to non-magnetic disorder in the host material, but there is a question that how it will be respect to magnetic impurities? For this, Yu, Shiba and Rusinov by considering impurity spins classically, deduced in-gap bound states known as Y SR states. This is an appropriate formalism for studying problem qualitatively but spins are quantum mechanical operators and for better understanding, should be treated in that way. In fact, in the last two chapters, we conclude that in the presence of magnetic ions in superconductors with s and p wave symmetry of gap function, system must undergo a phase transition to some new phase called heavy Fermi liquid which in fact is a state with strong correlation of conduction electrons with impurity ones. Also, in the Fermi liquid concept, there are quasi-particles emergence in this new phase that have large effective mass
  9. Keywords:
  10. Superconductivity ; Impurity ; Mean Field Approximation ; Anderson Impurity Model ; Quantum Correlation ; Kondo Lattice Model ; Bardeen-Cooper-Schrieffer Theory ; Energy Gap ; Magnetic Ions

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