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Effect of Angular Momentum of Light in Interaction with Dirac Matter
, M.Sc. Thesis Sharif University of Technology ; Jafari, Akbar (Supervisor) ; Miri, Mir Faez (Co-Advisor)
Abstract
In this project, we investigate the influence of angular momentum of Light on the Dirac matter. We show that polarization or spin of light can change the population of [pseudo-]spins. In graphene, pseudo-spins indicate the probability of existing elec-trons in each sub-lattice. However, the two different sub-lattices are the same and the contribution from two distinct Dirac cones cancel out. Therefore, the change in the population of pseudo-spins does not happen. On the other hand, in topological insulators we have just one Dirac cone; thus, polarization of light can change the population of [pseudo-]spins
The Present Status of Majorana Neutrin
, M.Sc. Thesis Sharif University of Technology ; Golshani, Mehdi (Supervisor)
Abstract
One of the most simple questions of particle physics, which is still unanswered, is whether neutrino and antineutrino are the same particles or not. The answer to this question has many implications for the physics beyond the Standard Model, supersymmetric theories and unified theories.
In this thesis we first introduce Majorana fermion, the best candidate for which is neutrino. Then its implications for going beyond the standard Model have been discussed. At present time, the most important experiment which can prove this guess is neutrinoless double beta decay which has been studied in details in this thesis. The study of the theoretical and experimental aspects of neutrinoless double...
In this thesis we first introduce Majorana fermion, the best candidate for which is neutrino. Then its implications for going beyond the standard Model have been discussed. At present time, the most important experiment which can prove this guess is neutrinoless double beta decay which has been studied in details in this thesis. The study of the theoretical and experimental aspects of neutrinoless double...
Electrical and Thermal Properties of Thin Films of Perovskites
, M.Sc. Thesis Sharif University of Technology ; Kargarian, Mehdi (Supervisor)
Abstract
In this thesis, we consider a simple layered structure grown along [001] direction. Based on the previous works we show that the energy spectrum contains linear Dirac spectrum of type II tilted in some direction. We also investigate the anomalous transport phenomena in the bilayer structures grown along [111] direction of a class of perovskites. The crystal field splits the d orbitals into two classes dubbed as eg and t2g described by different Hamiltonians within each manifold. An applied magnetic field breaks the time reversal symmetry and we show that the tight-binding bands acquire non-zero Chern numbers underlying the existence of non-trivial band topology in these structures. Again...
Optical Conductivity of Fermi Arc States
, M.Sc. Thesis Sharif University of Technology ; Jafari, Akbar (Supervisor)
Abstract
Recently, some materials, such as Weyl and Dirac semimetals, have been found in condensed matter physics whose band structure behaves like Weyl fermions of elementary particles near some points of the first Birillouin zone. The Weyl equation that governs these materials, have boundary because they are finite. By applying proper boundary conditions, two-dimensional surface states have been emerged. these states are called fermi arc sates because the surface corresponding to the fermi energy is not a closed surface. Surface states are mixed with bulk states because by getting close to the end of fermi arcs, surface states tend to bulk states con-tinuously. Being able to distinguish between...
Excitation spectrum of correlated Dirac fermions
, Article Journal of Physics: Conference Series, 14 January 2015 through 15 January 2015 ; Volume 603, Issue 1 , January , 2015 ; 17426588 (ISSN) ; Jafari, S. A ; Suzumura Y ; Matsuura H ; Fuseya Y ; Ogata M ; Sharif University of Technology
Institute of Physics Publishing
2015
Abstract
Motivated by the puzzling optical conductivity measurements in graphene, we speculate on the possible role of strong electronic correlations on the two-dimensional Dirac fermions. In this work we employ the slave-particle method to study the excitations of the Hubbard model on honeycomb lattice, away from half-filling. Since the ratio U/t ≈ 3.3 in graphene is not infinite, double occupancy is not entirely prohibited and hence a finite density of doublonscan be generated. We therefore extend the Ioff-Larkin composition rule to include a finite density of doublons. We then investigate the role played by each of these auxiliary particles in the optical absorption of strongly correlated Dirac...
Perpendicular andreev reflection: solid-state signature of black-hole horizon
, Article Physical Review B ; Volume 10, Issue 24 , 2019 ; 24699950 (ISSN) ; Jafari, A ; Sharif University of Technology
American Physical Society
2019
Abstract
Beenakker noticed that the peculiar band structure of Dirac fermions in two-dimensional (2D) solids allows for the specular Andreev reflection in these systems, which has no analogue in other 2D electron systems. An interesting deformation of the Dirac equation in the solid state is to tilt it, which has now been realized in materials. In this paper we report another peculiar feature of the Andreev reflection in tilted 2D Dirac cone systems. The tilt deformation of the Dirac equation is characterized by two parameters ζ=ζ(cosθ,sinθ). We show that when the tilt parameter is tuned to its "horizon value" ζ=1, irrespective of the incidence angle of electrons, the Andreev reflected hole is always...
Anderson Impurity Model in Dirac Matter
, Ph.D. Dissertation Sharif University of Technology ; Jafari, Akbar (Supervisor)
Abstract
In this thesis we have been mainly interested in studying Single Impurity Anderson model (SIAM) in Dirac fermions. Although this model seems to be simple, the rich physics of SIAM can not be underestimated. In this thesis we were interested in Dirac materials, systems which their low energy excitations are described by Dirac equation.Therefore, considering Dirac material in two dimensions(2D), we briefly review the distinct features of one atom thick layer of carbon. In addition, we will explain the effective Hamiltonian of Bismuth near L point which is considered a three dimensional(3D) Dirac material. Because of very strong spin-orbit interaction, bismuth is a key element in topological...
Collective excitations and the nature of Mott transition in undoped gapped graphene
, Article Journal of Physics Condensed Matter ; Volume 24, Issue 30 , 2012 ; 09538984 (ISSN) ; Sharif University of Technology
Abstract
The particle-hole continuum (PHC) for massive Dirac fermions provides an unprecedented opportunity for the formation of two collective split-off states, one in the singlet and the other in the triplet (spin-1) channel, when the short-range interactions are added to the undoped system. Both states are close in energy and are separated from the continuum of free particle-hole excitations by an energy scale of the order of the gap parameter Δ. They both disperse linearly with two different velocities, reminiscent of spin-charge separation in Luttinger liquids. When the strength of Hubbard interactions is stronger than a critical value, the velocity of singlet excitation, which we interpret as a...