arXiv subjects

Mohsen Modarresi

Publications and source records attributed to Mohsen Modarresi.

3 recordsLinked to original sources

arXiv2024

DMRG Analysis of Magnetic Order in the Zigzag Edges of Hexagonal CrN Nanoribbons

We investigate the finite temperature magnetic order at the edges of hexagonal CrN nanoribbons by using the density-functional theory combined with the density-matrix renormalization group method. Moreover, the spin-dependent transport in nanoribbons is calculated within the semi-classical Boltzmann transport theory. We find out that the zigzag edges have lower energy with respect to armchair edges. The zigzag edge of CrN nanoribbon shows half metallic electronic character which is the same as for the 2D monolayer. The localized electronic states on the zigzag edges reduce the electronic band gap energy for spin down electrons. The ab-initio electronic results are mapped into an effective 1D Heisenberg spin model up to the next nearest neighbor exchange interaction term. For zigzag ribbons, the nearest neighbor and next nearest neighbor magnetic exchange are around $10$ to $12$, and $-2$ to $0$~meV/Cr atom, respectively. The finite spin correlation length in 1D nanoribbons drops sharply to zero with temperature. The absence of long range spin correlations at the edges is a practical drawback for future room temperature 2D spintronic devices. The maximally localized Wannier functions are used for band interpolation and spin-dependent transport calculations by using the semi-classical Boltzmann equation. We show that zigzag edges of CrN are perfect spin filter under both electron and hole doping.

cond-mat.mes-hall↗

arXiv2017

Effects of interedge scattering on the Wigner crystallization in graphene nanoribbons

We investigate the effects of coupling between the two zigzag edges of graphene nanoribbons on the Wigner crystallization of electrons and holes using a combination of tight-binding, mean field Hubbard and many-body configuration interaction methods. We show that the thickness of the nanoribbon plays a crucial role in the formation of Wigner crystal. For ribbon widths smaller than 16 \mboxÅ, increased kinetic energy overcomes the long-range Coulomb repulsion and suppresses the Wigner crystallization. For wider ribbons up to 38 \mboxÅ wide, strong Wigner localization is observed for even number of electrons, revealing an even-odd effect also found in Coulomb blockade addition spectrum. Interedge correlations are found to be strong enough to allow simultaneous crystallization on both edges, although an applied electric field can decouple the two edges. Finally, we show that Wigner crystallization can also occurs for holes, albeit weaker than for electrons.

cond-mat.str-el↗

arXiv2015

Electrically Engineered Band Gap in Two-Dimensional Ge, Sn, and Pb: A First-Principles and Tight-Binding Approach

First-principles calculations were performed to investigate the electronic structure of two-dimensional (2-D) Ge, Sn, and Pb without and with the presence of an external electric field in combination with spin-orbit coupling. Tight-binding calculations based on four orbitals per atom and an effective single orbital are presented to match with the results obtained from first-principles calculations. In particular, the electronic band structure and the band splitting are investigated with both models. Moreover, the simple $k\cdot p$ model is also considered in order to understand the band splitting in the presence of an external electric field and spin-orbit coupling. A large splitting is obtained, which is expected to be useful for spintronic devices. The fair agreement between the first-principle, $k\cdot p$ model, and tight-binding approaches leads to a table of parameters for future tight-binding studies on hexagonal 2-D nanostructures. By using the tight binding parameters, the transport properties of typical 0-D triangular quantum dots between two semi-infinite electrodes in the presence of spin-orbit coupling are addressed.

cond-mat.mtrl-sci↗