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Investigation of the Effect of Disorder and Two Approches of Coherent Potential Approximation and Local Distribution

Esmail Zadeh Noghani, Fereshteh | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45425 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Jafari, Akbar
  7. Abstract:
  8. Disorders with creating the localized states, which are the states with limited spatial distribution, cause carriers of these states become limited to small part of space and cannot participate in the transport. If energy of these states is near the Fermi energy, the Anderson metal-insulator phase transition occurs. In this thesis,we studied type of disorders and determining their Hamiltonian and by studying definition of localization from different aspects, we attained a better explanation of disorders effects on materials. With studying the localization scaling theory, we ex-amined conditions of localization in different dimensions. Then for determining the green function and therefor the density of states of the nderson model, we studied two approaches: first we examined the mathematical method based on a generalization of Wgner’s model,which in case of same disorder distribution, agrees with Anderson model in Coherent-Potential-Approximation (CPA). We applied this model on raphene. In the end, we studied the Local Distribution approach (LD) with specific distribution function on the Bette lattice and we showed that CPA cannot describe the states near the band edge. Furthermore, we learned that we can consider the CPA approxima- tion as the average solution for the LD approximation
  9. Keywords:
  10. Disorder ; Localization ; Green Function ; Anderson Phase Transition ; Coherent-Potential Approximation ; Bethe Lattice

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