arXiv subjects

Niloufar Dadkhah

Publications and source records attributed to Niloufar Dadkhah.

3 recordsLinked to original sources

arXiv2026

Electronic and optical properties of arsenic monolayers: from planar honeycomb to the puckered phase

Group-V monolayer materials exhibit intriguing electronic and optical properties, influenced by their unique crystal symmetries and structural phases. In this work, we study arsenic monolayers, investigating their electronic and optical properties across different phases, including planar, and puckered forms, using density functional theory (DFT) and quasi-particle self-consistent $GW$ (QS$GW$) methods, with and without vertex contributions (ladder diagrams) and examine the effects of spin-orbit coupling and the orbital composition of the bands. The Bethe-Salpeter equation (BSE) method is used to study the optical response and the band origin of the low lying excitons is determined. The gradual transformation from the puckered $α$-phase to the flat honeycomb structure is studied under biaxial strain and the evolution of the band structure and optical response is described in terms of band inversions of bands of different orbital character.

cond-mat.mtrl-sci↗

arXiv2024

Band structure and excitonic properties of WSe$_2$ in the isolated monolayer limit in an all-electron approach

A study is presented of the electronic band structure and optical absorption spectrum of monolayer WSe$_2$ using an all-electron quasiparticle self-consistent $GW$ approach, QS$G\hat W$, in which the screened Coulomb interaction $\hat W$ is calculated including ladder diagrams representing electron-hole interaction. The Bethe-Salpeter Equation is used to calculate both the screened Coulomb interaction $\hat W$ in the quasiparticle band structure and the imaginary part of the macroscopic dielectric function. The convergence of the quasiparticle band gap and lowest exciton peak position is studied as function of the separation of the monolayers when using periodic boundary conditions. The quasiparticle gap is found to vary as $1/d$ with $d$ the size of the vacuum separation, while the excitonic lowest peak reaches convergence much faster. The nature of the exciton spectrum is analyzed and shows several excitonic peaks below the quasiparticle gap when a sufficient number of $\textbf{k}$ points is used. They are found to be in good agreement with prior work and experiment after adding spin-orbit coupling corrections and can be explained in the context of the Wannier-Mott theory adapted to 2D.

cond-mat.mtrl-sci↗

arXiv2023

Improved quasiparticle self-consistent electronic band structure and excitons in $β$-LiGaO$_2$

The band structure of $β$-LiGaO$_2$ is calculated using the quasiparticle self-consistent QS$G\hat W$ method where the screened Coulomb interaction $\hat W$ is evaluated including electron-hole interaction ladder diagrams and $G$ is the one-electron Green's function. Improved convergence compared to previous calculations leads to a significantly larger band gap of about 7.0 eV. However, exciton binding energies are found to be large and lead to an exciton gap of about 6.0 eV if also a zero-point-motion correction of about $-0.4$ eV is included. These results are in excellent agreement with recent experimental results on the onset of absorption. Besides the excitons observed thus far, the calculations indicate the existence of a Rydberg-like series of exciton excited states, which is however modified from the classical Wannier exciton model by the anisotropies of the material and the more complex mixing of Bloch states in the excitons resulting from the Bethe-Salpeter equation. The exciton fine structure and the exciton wave functions are visualized and analyzed in various ways.

cond-mat.mtrl-sci↗