Browsing by Author "Asgari, R."

Now showing 1 - 16 of 16

Open Access
Comparative study of screened interlayer interactions in the Coulomb drag effect in bilayer electron systems
(The American Physical Society, 2008) Asgari, R.; Tanatar, Bilal; Davoudi, B.
Coulomb drag experiments in which the interlayer resistivity is measured are important as they provide information on the Coulomb interactions in bilayer systems. When the layer densities are low correlation effects become significant to account for the quantitative description of experimental results. We investigate systematically various models of effective interlayer interactions in a bilayer system and compare our results with recent experiments. In the low density regime, the correlation effects are included via the intra- and interlayer local-field corrections. We employ several theoretical approaches to construct static local-field corrections. Our comparative study demonstrates the importance of including the correlation effects accurately in the calculation of drag resistivity. Recent experiments performed at low layer densities are adequately described by effective interlayer interactions incorporating static correlations.
Open Access
Composite quasiparticles in strongly correlated dipolar Fermi liquids
(American Physical Society, 2018) Seydi, I.; Abedinpour, S. H.; Asgari, R.; Tanatar, Bilal
Strong particle-plasmon interaction in electronic systems can lead to composite hole-plasmon excitations. We investigate the emergence of similar composite quasiparticles in ultracold dipolar Fermi liquids originating from the long-range dipole-dipole interaction. We use the G0W technique with an effective interaction obtained from the static structure factor to calculate the quasiparticle properties and single-particle spectral function. We first demonstrate that within this formalism a very good agreement with the quantum Monte Carlo results could be achieved over a wide range of coupling strengths for the renormalization constant and effective mass. The composite quasiparticle-zero sound excitations which are undamped at long wavelengths emerge at intermediate and strong couplings in the spectral function and should be detectable through the radio frequency spectroscopy of nonreactive polar molecules at high densities.
Open Access
Correlations in charged fermion-boson mixture in dimensionalities D = 2 and D = 3
(Elsevier B.V., 2006) Asgari, R.; Tanatar, Bilal
We numerically study the correlation effects in a two-component charged fermion-boson mixture at zero temperature investigating the role played by the statistical effects and Coulomb correlations in a model with different fermion and boson mass ratios in two and three dimensions. The local-field factors describing the correlation effects and collective excitation modes are determined through the self-consistent scheme. We find that the effects of correlations and statistics are more pronounced in two-dimensional mixtures.
Open Access
Effect of disorder on the ground-state properties of graphene
(The American Physical Society, 2008) Asgari, R.; Vazifeh, M. M.; Ramezanali, M. R.; Davoudi, E.; Tanatar, Bilal
We calculate the ground-state energy of Dirac electrons in graphene in the presence of disorder. We take randomly distributed charged impurities at a fixed distance from the graphene sheet and surface fluctuations (ripples) as the main scattering mechanisms. A mode-coupling approach to the scattering rate and random-phase approximation for the ground-state energy incorporating the many-body interactions and the disorder effects yields good agreement with the experimental inverse compressibility.
Open Access
Effective electron-electron interactions and magnetic phase transition in a two-dimensional electron liquid
(Elsevier B.V., 2007) Asgari, R.; Esmailian, A.; Tanatar, Bilal
We investigate the spin-dependent effective electron-electron interactions in a uniform system of two-dimensional electrons to understand the spontaneous magnetization expected to occur at very low density. For this purpose, we adopt the Kukkonen-Overhauser form for the effective interactions which are built by accurately determined local-field factors describing the charge and spin fluctuations. The critical behavior of the effective interaction for parallel spin electrons allows us to quantitatively locate the transition to the ferromagnetic state at rs ≈ 27. When the finite width effects are approximately taken into account the transition occurs at rs ≈ 30 in agreement with recent quantum Monte Carlo calculations.
Open Access
Effective mass enhancement in two-dimensional electron systems: The role of interaction and disorder effects
(Elsevier, 2004) Asgari, R.; Davoudi, B.; Tanatar, Bilal
Recent experiments on two-dimensional (2D) electron systems have found a sharp increase in the effective mass of electrons with decreasing electron density. In an effort to understand this behavior we employ the many-body theory to calculate the quasiparticle effective mass in 2D electron systems. Because the low density regime is explored in the experiments we use the GWγ approximation where the vertex correction γ describes the correlation effects to calculate the self-energy from which the effective mass is obtained. We find that the quasiparticle effective mass shows a sharp increase with decreasing electron density. Disorder effects due to charged impurity scattering plays a crucial role in density dependence of effective mass.
Open Access
Effective mass suppression in a ferromagnetic two-dimensional electron liquid
(The American Physical Society, 2009) Asgari, R.; Gokmen, T.; Tanatar, Bilal; Padmanabhan, M.; Shayegan, M.
We present numerical calculations of the electron effective mass in an interacting ferromagnetic two-dimensional electron system. We consider quantum interaction effects associated with the charge-density fluctuation-induced many-body vertex corrections. Our theory, which is free of adjustable parameters, reveals that the effective mass is suppressed (relative to its band value) in the strong-coupling limit, in good agreement with recent experimental results. © 2009 The American Physical Society.
Open Access
Effects of disorder on the ground-state energy of a two-dimensional electron gas
(The American Physical Society, 2002) Asgari, R.; Tanatar, Bilal
We study the effects of disorder scattering on the ground-state energy of a two-dimensional electron system.Considering charged impurity scattering within the mode-coupling approximation to the memory functionformalism, we calculate the correlation effects using a self-consistent field approach. In a different model, wealso treat the disorder effects phenomenologically. The exchange, correlation, and ground-state energies andthe compressibility are calculated for both models. In terms of the compressibility both models have similarpredictions in the high-density region. The mode-coupling theory results at lower density are in better quali-tative agreement with the experimental findings
Open Access
Exchange-Correlation effects and the quasiparticle properties in a two-dimensional dipolar fermi liquid
(Springer, 2020) Seydi, I.; Abedinpour, S. H.; Asgari, R.; Tanatar, Bilal
We investigate the effects of exchange and correlation on the quasiparticle properties such as the self-energy, the many-body effective mass and the renormalization constant in a two-dimensional system of ultracold dipolar fermions with dipole moments aligned in the perpendicular direction to the plane. We use the G0W approximation along with the generalized random phase approximation, where the many-body effects have been incorporated in the effective interaction W through the Hubbard local-field factor. The many-body effective mass and the renormalization constant are reduced with the increase of coupling strength. We also study the effect of dipole-dipole interaction on the single-particle spectral function of the two dimensional dipolar Fermi liquid. We observe composite hole-zero sound excitation which is a bound state of quasiparticles with the collective mode (i.e. zero-sound) at intermediate and high coupling constants. These composite excitations are undamped at small wave vectors. Due to repulsion between quasiparticle and composite excitation resonances, we find a gap-like feature between quasiparticle and composite excitation dispersions at long wavelengths.
Open Access
Ground-state and dynamical properties of two-dimensional dipolar Fermi liquids
(Elsevier Inc., 2014-01) Abedinpour, S. H.; Asgari, R.; Tanatar, Bilal; Polini, M.
We study the ground-state properties of a two-dimensional spin-polarized fluid of dipolar fermions within the Euler-Lagrange Fermi-hypernetted-chain approximation. Our method is based on the solution of a scattering Schrödinger equation for the "pair amplitude" g(r), where g ( r) is the pair distribution function. A key ingredient in our theory is the effective pair potential, which includes a bosonic term from Jastrow-Feenberg correlations and a fermionic contribution from kinetic energy and exchange, which is tailored to reproduce the Hartree-Fock limit at weak coupling. Very good agreement with recent results based on quantum Monte Carlo simulations is achieved over a wide range of coupling constants up to the liquid-to-crystal quantum phase transition. Using the fluctuation-dissipation theorem and a static approximation for the effective inter-particle interactions, we calculate the dynamical density-density response function, and furthermore demonstrate that an undamped zero-sound mode exists for any value of the interaction strength, down to infinitesimally weak couplings.
Open Access
Hard-core Yukawa model for two-dimensional charge-stabilized colloids
(American Physical Society, 2001-10) Asgari, R.; Davoudi, B.; Tanatar, Bilal
The hypernetted chain and Percus-Yevick approximations are used to study the phase diagram of a simple hard-core Yukawa model of charge-stabilized colloidal particles in a two-dimensional system. We calculate the static structure factor and the pair distribution function over a wide range of parameters. Using static correlation functions, we present an estimate for the liquid-solid phase diagram for a wide range of parameters.
Open Access
Many-body effective mass and spin susceptibility in a quasi-two-dimensional electron liquid
(The American Physical Society, 2006) Asgari, R.; Tanatar, Bilal
We present numerical calculations of the effect of electron-electron interactions on the quasiparticle properties such as the effective mass and the Landé g -factor in a GaAs AlGaAs triangular quantum well from which the spin susceptibility is obtained. For this purpose, we consider quantum many-body effects associated with charge- and spin-density fluctuations induced many-body vertex corrections. The approach is based on the many-body local-field factors which are extracted from Fermi hypernetted-chain self-consistent calculation through the fluctuation-dissipation theorem. We find the spin susceptibility in good agreement with the recent experimental measurements and quantum Monte Carlo simulation data for such a system in the weak and intermediate coupling limits.
Open Access
Quasi-particle properties in a quasi-two-dimensional electron liquid
(Indian Academy of Sciences, 2008) Asgari, R.; Tanatar, Bilal
We consider the quasi-particle properties such as the effective mass and spin susceptibility of quasi-two-dimensional electron systems. The finite quantum well width effects are incorporated into the local-field factors that describe the charge and spin correlations. We employ the Fermi-hypernetted chain formalism in conjunction with fluctuation-dissipation theorem to obtain the local-field factors. Our results are in good agreement with recent experiments.
Open Access
Rotons and Bose condensation in Rydberg-dressed Bose gases
(American Physical Society, 2020) Seydi, I.; Abedinpour, S. H.; Zillich, R. E.; Asgari, R.; Tanatar, Bilal
We investigate the ground-state properties and excitations of Rydberg-dressed bosons in both three and two dimensions, using the hypernetted-chain Euler-Lagrange approximation, which accounts for correlations and thus goes beyond the mean-field approximation. The short-range behavior of the pair distribution function signals the instability of the homogeneous system with respect to the formation of droplet crystals at strong couplings and large soft-core radius. This tendency to spatial density modulation coexists with off-diagonal long-range order. The contribution of the correlation energy to the ground-state energy is significant at large coupling strengths and intermediate values of the soft-core radius while for a larger soft-core radius the ground-state energy is dominated by the mean-field (Hartree) energy. We have also performed path integral Monte Carlo simulations at selected system parameters to verify the performance of our hypernetted-chain Euler-Lagrange results in three dimensions. In the homogeneous phase, the two approaches are in very good agreement. Moreover, Monte Carlo simulations predict a first-order quantum phase transition from a homogeneous superfluid phase to the quantum droplet phase with face-centered cubic symmetry for Rydberg-dressed bosons in three dimensions.
Open Access
Rydberg-dressed Fermi liquid: correlations and signatures of droplet crystallization
(American Physical Society, 2021-04-07) Seydi, I.; Abedinpour, S. H.; Asgari, R.; Panholzer, M.; Tanatar, Bilal
We investigate the effects of many-body correlations on the ground-state properties of a single-component ultracold Rydberg-dressed Fermi liquid with purely repulsive interparticle interactions in both three and two spatial dimensions. We employed the Fermi-hypernetted-chain Euler-Lagrange approximation and observed that the contribution of the correlation energy on the ground-state energy becomes significant at intermediate values of the soft-core radius and large coupling strengths. For small and large soft-core radii, the correlation energy is negligible and the ground-state energy approaches the Hartree-Fock value. The positions of the main peaks in static structure factor and pair distribution function in the homogeneous fluid phase signal the formation of quantum droplet crystals with several particles confined inside each droplet.
Open Access
Static local-field factors in a two-dimensional electron liquid
(The American Physical Society, 2006) Asgari, R.; Subaşi, A. L.; Sabouri-Dodaran, A. A.; Tanatar, Bilal
We present a numerical calculation for the static spin-symmetric and spin-antisymmetric local-field factors as a function of density in a two-dimensional (2D) unpolarized electron liquid. We use a recent analytical expression for the spin-resolved pair distribution function of a 2D electron liquid based on quantum Monte Carlo simulation data and accurate correlation energy as input to construct the local-field factors from the fluctuation-dissipation theorem. We obtain good agreement with data from quantum Monte Carlo studies of the 2D electron liquid over an extensive range of density.