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honeycomb-lattices
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Mott Transition in Ordered and Disordered Honeycomb Lattice Using Strong-coupling Perturbation Theory
, Ph.D. Dissertation Sharif University of Technology ; Jafari, Akbar (Supervisor)
Abstract
The ability to determine the nature of the low temperature state of the interacting quantum system is one of the main goals of condensed matter theory. Nevertheless, despite ongoing efforts, no single method has proved to work perfectly for interacting systems. In this thesis, we employ the strong-coupling perturbation theory which corresponds to an expansion in powers of the hopping t around the atomic limit. So, first the strong-coupling perturbation theory is introduced. Next we apply this approach to the half-filled Hubbard model on honeycomb lattice. Within this approach, we are able to obtain an analytical form for single-particle gap, extracted from density of state, as a function of...
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...
Phase diagram and thermal Hall conductivity of the spin-liquid Kekulé-Kitaev model
, Article Physical Review B ; Volume 101, Issue 11 , March , 2020 , Pages: 11-15 ; Kargarian, M ; Langari, A ; Sharif University of Technology
American Physical Society
2020
Abstract
In this work we study the phase diagram of the Kekulé-Kitaev model. The model is defined on a honeycomb lattice with bond-dependent anisotropic exchange interactions, making it exactly solvable in terms of Majorana representation of spins, in close analogy to the Kitaev model. However, the energy spectrum of Majorana fermions has a multiband structure characterized by Chern numbers 0, ±1, and ±2. We obtained the phase diagram of the model in the plane of exchange couplings and in the presence of a magnetic field and found chiral topological and trivial spin-liquid ground states. In the absence of magnetic field most of the phase diagram is a trivial gapped phase continuously connected to an...
Plaquette valence bond ordering in a J1-J2 Heisenberg antiferromagnet on a honeycomb lattice
, Article Journal of Physics Condensed Matter ; Volume 23, Issue 22 , 2011 ; 09538984 (ISSN) ; Shahbazi, F ; Jafari, S. A ; Sharif University of Technology
Abstract
We study an S = 1/2 Heisenberg model on the honeycomb lattice with first and second neighbor antiferromagnetic exchange (J1-J2 model), employing exact diagonalization in both the Sz = 0 basis and nearest neighbor singlet valence bond (NNVB) basis. We find that for 0.2 < J2/J1 < 0.3, the NNVB basis gives a proper description of the ground state in comparison with the exact results. By analyzing the dimer-dimer as well as the plaquette-plaquette correlations and also defining appropriate structure factors, we investigate possible symmetry breaking states as the candidates for the ground state in the frustrated region. We provide a body of evidence in favor of plaquette valence bond ordering...
Phase transitions in the binary-alloy Hubbard model: Insights from strong-coupling perturbation theory
, Article Physical Review B ; Volume 99, Issue 1 , 2019 ; 24699950 (ISSN) ; Habibi, A ; Jafari, S. A ; Sharif University of Technology
American Physical Society
2019
Abstract
In the binary alloy with composition AxB1-x of two atoms with ionic energy scales ±Δ, an apparent Anderson insulator (AI) is obtained as a result of randomness in the position of atoms. Using our recently developed technique that combines the local self-energy from strong-coupling perturbation theory with the transfer matrix method, we are able to address the problem of adding a Hubbard U to the binary-alloy problem for millions of lattice sites on the honeycomb lattice. By adding the Hubbard interaction U, the resulting AI phase will become metallic, which in our formulation can be manifestly attributed to the screening of disorder by Hubbard U. Upon further increase in U, again the AI...
Graphene: Promises, facts, opportunities, and challenges in nanomedicine
, Article Chemical Reviews ; Volume 113, Issue 5 , 2013 , Pages 3407-3424 ; 00092665 (ISSN) ; Laurent, S ; Chen, W ; Akhavan, O ; Imani, M ; Ashkarran, A. A ; Mahmoudi, M ; Sharif University of Technology
2013
Abstract
Graphene, a two-dimensional (2D) sheet of sp2-hybridized carbon atoms packed into a honeycomb lattice, has led to an explosion of interest in the field of materials science, physics, chemistry, and biotechnology since the few-layers graphene (FLG) flakes were isolated from graphite in 2004. For an extended search, derivatives of nanomedicine such as biosensing, biomedical, antibacterial, diagnosis, cancer and photothermal therapy, drug delivery, stem cell, tissue engineering, imaging, protein interaction, DNA, RNA, toxicity, and so on were also added. Since carbon nanotubes are normally described as rolled-up cylinders of graphene sheets and the controllable synthesis of nanotubes is well...
Van der Waals energy surface of a carbon nanotube sheet
, Article Solid State Communications ; Volume 152, Issue 3 , February , 2012 , Pages 225-230 ; 00381098 (ISSN) ; Shayeganfar, F ; Neek Amal, M ; Sharif University of Technology
Abstract
The van der Walls interaction between a carbon nanotube sheet (CNTS) and a rare gas atom, is studied using both atomistic and continuum approaches. We present analytical expressions for the van der Waals energy of continuous nanotubes interacting with a rare gas atom. It is found that the continuum approach does not properly treat the effect of atomistic configurations on the energy surfaces. The energy barriers are small as compared to the thermal energy, which implies the free motion above the CNTS in heights about one nanometer. In contrast to the energy surface of a graphene sheet, the honeycomb lattice structure in the energy surface of a CNTS is imperceivable. Defects alter the energy...
Magnetoelastic coupling enabled tunability of magnon spin current generation in two-dimensional antiferromagnets
, Article Physical Review B ; Volume 104, Issue 18 , 2021 ; 24699950 (ISSN) ; Hamdi, M ; Park, S ; Khavasi, A ; Mohseni, S. M ; Sadeghi, A ; Sharif University of Technology
American Physical Society
2021
Abstract
We theoretically investigate the magnetoelastic coupling (MEC) and its effect on magnon transport in two-dimensional antiferromagnets with a honeycomb lattice. MEC coefficients along with magnetic exchange parameters and spring constants are computed for monolayers of transition-metal trichalcogenides with Néel magnetic order (MnPS3 and VPS3) and zigzag order (CrSiTe3, NiPS3, and NiPSe3) by ab initio calculations. Using these parameters, we predict that the spin-Nernst coefficient is significantly enhanced due to magnetoelastic coupling. Our study shows that although Dzyaloshinskii-Moriya interaction can produce spin-Nernst effect in these materials, other mechanisms such as magnon-phonon...