arXiv subjects

R. Asgari

Publications and source records attributed to R. Asgari.

At least 19 recordsLinked to original sources

arXiv2016

Electron mobility of a two-dimensional electron gas at the interface of SrTiO$_3$ and LaAlO$_3$

We calculate the mobility of a two-dimensional electron gas residing at the interface of LaAlO$_{3}$/SrTiO$_{3}$ following a three band Boltzmann approach at low temperature, where carrier-charged impurity scattering process is assumed to be dominant. We explain the anisotropic characteristic of the dielectric function, which is a consequence of elliptical bands close to Fermi surface. The screening effect, which weakens the long-range Coulomb interaction of the electron-impurity is considered within the random phase approximation. Working at carrier densities high enough to neglect the spin-orbit induced splitting of the bands, we find that the mobility varies inversely with the cubic power of the carrier density ($n_{2D}^{-3}$) in good agreement with the experimental results. We also investigate the role of variable dielectric constant of SrTiO$_{3}$, the multiband nature of the system and interband interactions in exploring this result.

cond-mat.mes-hall↗

arXiv2008

Quasiparticle properties of graphene in the presence of disorder

We calculate the quasiparticle properties of chiral two-dimensional Dirac electrons in graphene within the Landau Fermi Liquid scheme based on $GW$ approximation in the presence of disorder. Disorder effects due to charged impurity scattering plays a crucial role in density dependence of quasiparticle quantities. Mode-coupling approach to scattering rate and self-energy in $GW$ approximation for quasiparticle renormalized Fermi velocity and spin-antisymmetric Landau Fermi parameter incorporating the many-body interactions and the disorder effects show reduction of these quantities by 5-15 percent at available experimental charge carrier density region.

cond-mat.mes-hall↗

arXiv2008

Effect of disorder on the ground-state properties of graphene

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. Mode-coupling approach to scattering rate and random-phase approximation for ground-state energy incorporating the many-body interactions and the disorder effects yields good agreement with experimental inverse compressibility.

cond-mat.mes-hall↗

arXiv2008

Comparative study of screened inter-layer interactions in the Coulomb drag effect in bilayer electron systems

Coulomb drag experiments in which the inter-layer 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 inter-layer 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 inter-layer 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 inter-layer interactions incorporating static correlations.

cond-mat.mes-hall↗

arXiv2007

Ground-state properties of the one dimensional electron liquid

We present a theory of the pair distribution function $g(z)$ and many-body effective electron-electron interaction for one dimensional (1D) electron liquid. Our approach involves the solution of a zero-energy scattering Schrödinger equation for $\sqrt{g(z)}$ where we implemented the Fermi hypernetted-chain approximation including the elementary diagrams corrections. We present numerical results for $g(z)$ and the static structure factor $S(k)$ and obtain good agreement with data from diffusion Monte Carlo studies of the 1D system. We calculate the correlation energy and charge excitation spectrum over an extensive range of electron density. Furthermore, we obtain the static correlations in good qualitative agreement with those calculated for the Luttinger liquid model with long-range interactions.

cond-mat.str-el↗

arXiv2007

Ground state properties of a confined simple atom by C$_{60}$ fullerene

We numerically study the ground state properties of endohedrally confined hydrogen (H) or helium (He) atom by a molecule of C$_{60}$. Our study is based on Diffusion Monte Carlo method. We calculate the effects of centered and small off-centered H- or He-atom on the ground state properties of the systems and describe the variation of ground state energies due to the C$_{60}$ parameters and the confined atomic nuclei positions. Finally, we calculate the electron distributions in $x-z$ plane in a wide range of C$_{60}$ parameters.

cond-mat.other↗

arXiv2007

Analytic theory of pair distribution functions in symmetric electron-electron and electron-hole bilayers

We present a self-consistent analytic theory of the intra-layer and inter-layer pair correlation functions in electron-electron and electron-hole fluid bilayer systems. Our approach involves the solution of a zero-energy scattering Schroedinger equation with an effective potential which includes a Bose-like term from Jastrow-Feenberg correlations and a Fermi term from kinetic energy and exchange, tailored to yield the Hartree-Fock limit at high carrier density. The theory is also shown to satisfy the plasmon sum rule and the charge neutrality condition. We obtain good agreement with the available Quantum Diffusion Monte Carlo (DMC) data in symmetric bilayers over a wide range of carrier density and layer spacing, and stress the role of three-body correlation terms in yielding fully quantitative agreement at strong coupling. Signals of impending transitions to density-modulated states at strong coupling and low layer spacing appear in the calculated pair correlations through inter-layer in-phase oscillations for electron-hole bilayers and out-of-phase oscillations for electron-electron bilayers, in agreement with the DMC findings.

cond-mat.mes-hall↗

arXiv2005

Ground-state densities and pair correlation functions in parabolic quantum dots

We present an extensive comparative study of ground-state densities and pair distribution functions for electrons confined in two-dimensional parabolic quantum dots over a broad range of coupling strength and electron number. We first use spin-density-functional theory to determine spin densities that are compared with Diffusion Monte Carlo (DMC) data. This accurate knowledge of one-body properties is then used to construct and test a local approximation for the electron-pair correlations. We find very satisfactory agreement between this local scheme and the available DMC data, and provide a detailed picture of two-body correlations in a coupling-strength regime preceding the formation of Wigner-like electron ordering.

cond-mat.mes-hall↗

arXiv2004

Many-body effective mass enhancement in a two-dimensional electron liquid

Motivated by a large number of recent magnetotransport studies we have revisited the problem of the microscopic calculation of the quasiparticle effective mass in a paramagnetic two-dimensional (2D) electron liquid (EL). Our systematic study is based on a generalized $GW$ approximation which makes use of the many-body local fields and takes advantage of the results of the most recent QMC calculations of the static charge- and spin-response of the 2D EL. We report extensive calculations for the many-body effective mass enhancement over a broad range of electron densities. In this respect we critically examine the relative merits of the on-shell approximation, commonly used in weak-coupling situations, {\it versus} the actual self-consistent solution of the Dyson equation. We show that already for $r_s \simeq 3$ and higher, a solution of the Dyson equation proves here necessary in order to obtain a well behaved effective mass. Finally we also show that our theoretical results for a quasi-2D EL, free of any adjustable fitting parameters, are in good qualitative agreement with some recent measurements in a GaAs/AlGaAs heterostructure.

cond-mat.mes-hall↗

arXiv2004

Self-consistent Overhauser model for the pair distribution function of an electron gas at finite temperature

We present calculations of the spin-averaged pair distribution function $g(r)$ in a homogeneous gas of electrons moving in dimensionality D=3 or D=2 at finite temperature. The model involves the solution of a two-electron scattering problem via an effective potential which embodies many-body effects through a self-consistent Hartree approximation, leading to two-body wave functions to be averaged over a temperature-dependent distribution of relative momentum for electron pairs. We report illustrative numerical results for $g(r)$ in an intermediate-coupling regime and interpret them in terms of changes of short-range order with increasing temperature.

cond-mat.mes-hall↗

arXiv2004

Quasiparticle self-energy and many-body effective mass enhancement in a two-dimensional electron liquid

Motivated by a number of recent experimental studies we have revisited the problem of the microscopic calculation of the quasiparticle self-energy and many-body effective mass enhancement in a two-dimensional electron liquid. Our systematic study is based on the many-body local fields theory and takes advantage of the results of the most recent Diffusion Monte Carlo calculations of the static charge and spin response of the electron liquid. We report extensive calculations of both the real and imaginary parts of the quasiparticle self-energy. We also present results for the many-body effective mass enhancement and the renormalization constant over an extensive range of electron density. In this respect we critically examine the relative merits of the on-shell approximation versus the self-consistent solution of the Dyson equation. We show that in the strongly-correlated regime a solution of the Dyson equation proves necessary in order to obtain a well behaved effective mass. The inclusion of both charge- and spin-density fluctuations beyond the Random Phase Approximation is indeed crucial to get reasonable agreement with recent measurements.

cond-mat.mes-hall↗

arXiv2004

Analytic theory of correlation energy and spin polarization in the 2D electron gas

We present an analytic theory of the pair distribution function and the ground-state energy in a two-dimensional (2D) electron gas with an arbitrary degree of spin polarization. Our approach involves the solution of a zero-energy scattering Schrödinger equation with an effective potential which includes a Fermi term from exchange and kinetic energy and a Bose-like term from Jastrow-Feenberg correlations. The form of the latter is assessed from an analysis of data on a 2D gas of charged bosons. We obtain excellent agreement with data from quantum Monte Carlo studies of the 2D electron gas. In particular, our results for the correlation energy show a quantum phase transition occurring at coupling strength $r_s\approx 24$ from the paramagnetic to the fully spin-polarized fluid.

cond-mat.str-el↗

arXiv2004

Effective mass enhancement in two-dimensional electron systems: the role of interaction and disorder effects

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.

cond-mat.mes-hall↗

arXiv2003

Correlation energy of a two-dimensional electron gas from static and dynamic exchange-correlation kernels

We calculate the correlation energy of a two-dimensional homogeneous electron gas using several available approximations for the exchange-correlation kernel $f_{\rm xc}(q,ω)$ entering the linear dielectric response of the system. As in the previous work of Lein {\it et al.} [Phys. Rev. B {\bf 67}, 13431 (2000)] on the three-dimensional electron gas, we give attention to the relative roles of the wave number and frequency dependence of the kernel and analyze the correlation energy in terms of contributions from the $(q, iω)$ plane. We find that consistency of the kernel with the electron-pair distribution function is important and in this case the nonlocality of the kernel in time is of minor importance, as far as the correlation energy is concerned. We also show that, and explain why, the popular Adiabatic Local Density Approximation performs much better in the two-dimensional case than in the three-dimensional one.

cond-mat.mes-hall↗

arXiv2003

Analytic theory of ground-state properties of a three-dimensional electron gas at varying spin polarization

We present an analytic theory of the spin-resolved pair distribution functions $g_{σσ'}(r)$ and the ground-state energy of an electron gas with an arbitrary degree of spin polarization. We first use the Hohenberg-Kohn variational principle and the von Weizsäcker-Herring ideal kinetic energy functional to derive a zero-energy scattering Schrödinger equation for $\sqrt{g_{σσ'}(r)}$. The solution of this equation is implemented within a Fermi-hypernetted-chain approximation which embodies the Hartree-Fock limit and is shown to satisfy an important set of sum rules. We present numerical results for the ground-state energy at selected values of the spin polarization and for $g_{σσ'}(r)$ in both a paramagnetic and a fully spin-polarized electron gas, in comparison with the available data from Quantum Monte Carlo studies over a wide range of electron density.

cond-mat.str-el↗

arXiv2002

Pair densities at contact in the quantum electron gas

The value of the pair distribution function g(r) at contact (r = 0) in a quantum electron gas is determined by the scattering events between pairs of electrons with antiparallel spins. The theoretical results for g(0) as a function of the coupling strength r_s in the paramagnetic electron gas in dimensionality D=2 and 3, that have been obtained from the solution of the two-body scattering problem with a variety of effective scattering potentials embodying many-body effects, are compared with the results of many-body calculations in the ladder approximation and with quantum Monte Carlo data.

cond-mat.str-el↗

arXiv2002

Self-consistent scattering theory of the pair distribution function in charged Bose fluids

We use a density functional theoretical approach to calculate the pair distribution function and the effective interactions in homogeneous fluids of spinless charged bosons. The scheme involves the self-consistent solution of a two-particle scattering problem with an effective scattering potential which embodies many-body effects and is adjusted to the compressibility sum rule. Numerical results are presented over an extensive range of density in both three and two dimensions.

cond-mat.soft↗

arXiv2002

Self-consistent theory of pair distribution functions and effective interactions in quantum Coulomb liquids

We use a density-functional theoretical approach to set up a computationally simple self-consistent scheme to calculate the pair distribution functions and the effective interactions in quantum Coulomb liquids. We demonstrate the accuracy of the approach for different statistics and space dimensionalities by reporting results for a two-dimensional electron gas and for a three-dimensional boson plasma over physically relevant ranges of coupling strength, in comparison with Monte Carlo data.

cond-mat.str-el↗