Hamze Mousavi

Graphene as Gas Sensors

The triatomic and tetratomic gas molecule adsorption effects on the electrical conductivity of graphene are investigated by the tight-binding model, Greens function method, and coherent potential approximation. We find that the electrical conductivity of graphene sheet is sensitive to the adsorption of these gases.

Controlling the Bandgap of Boron Nitride Nanotubes with Carbon Doping

This study explores the effects of doping by carbon (C) atoms on electronic properties of (10,10) and (16,0) boron nitride (BN) nanotubes (NTs). We exploit the random tight-binding model with Green’s function technique and coherent potential approximation to show that the C dopant causes a decrease in the bandgap of the BN NTs, and their matching Van Hove singularities (VHS) in the density of states (DOS) are broadened. When the impurity concentration is large enough, the form of the DOS of the BN NTs becomes similar to that of metallic (10,10) and semiconducting (16,0) C NTs and their VHS get sharpened. This work might provide opportunities for creating new optoelectronic devices based on BN honeycomb nanosystems.

Flake electrical conductivity of few-layer graphene.

The Kubo formula for the electrical conductivity of per stratum of few-layer graphene, up to five, is analytically calculated in both simple and Bernal structures within the tight-binding Hamiltonian model and Greens function technique, compared with the single-layer one. The results show that, by increasing the layers of the graphene as well as the interlayer hopping of the nonhybridized p z orbitals, this conductivity decreases. Although the change in its magnitude varies less as the layer number increases to beyond two,distinguishably, at low temperatures, it exhibits a small deviation from linear behavior. Moreover, the simple bilayer graphene represents more conductivity with respect to the Bernal case.

Heat capacity of hexagonal boron nitride sheet in Holstein model

The effects of electron-phonon interaction on the electronic heat capacity of hexagonal boron nitride plane are investigated within the Holstein Hamiltonian model and Green’s function formalism. By using different electron-phonon coupling constants of boron and nitrogen sublattices, it is found that the specific heat has different behaviors in two temperature regions. In the low temperature region, the electronphonon interaction causes the enhancement of specific heat due to decreasing the band gap, while heat capacity reduces in the high temperature region because of decreasing the excitation spectrum.

Optical Conductivity of Graphene Sheet Including Electron-Phonon Interaction

Using an expression of optical conductivity, based on the linear response theory, the Greens function technique and within the Holstein Hamiltonian model, the effect of electron-phonon interaction on the optical conductivity of graphene plane is studied. It is found that the electron-phonon coupling increases the optical conductivity of graphene sheet in the low frequency region due to decreasing quasiparticle weight of electron excitation while the optical conductivity reduces in the high frequency region. The latter is due to role of electrical fields frequency.

Investigation of non-magnetic impurity doping effect on the MgB2 superconductor critical temperature

We have investigated the effect of finite non-magnetic impurity doping concentration on the critical temperature (Tc) of the MgB2 superconductor by using the coherent potential approximation. We found, by choosing the chemical potential μ = −0.47t and scattering strength δ = 4.5t, that Tc is reduced with impurity concentration similarly to the measured experimental results.

The Hall conductivity of graphene

Sensitivity of the Hall conductivity of graphene plane to gas molecule adsorption is investigated within the coherent potential approximation for the tight-binding model Hamiltonian. The results show that the Hall conductivity of system have a limit change when finite triatomic and tetratomic gas molecules adsorb and act as acceptors or donors.

Electronic specific heat of carbon nanotubes

The effects of electron–phonon interaction on the temperature dependence of the specific heat of (10, 0) zigzag semiconducting carbon nanotubes are studied. The Greens function formalism within the Holstein Hamiltonian model is used. It is found that the electronic specific heat capacity gives different behaviors in two temperature regions. In the low-temperature region, the electron–phonon interaction causes the specific heat to increase due to the band gap decreasing, whereas the heat capacity decreases in the high temperature region due to the excitation spectrum decreasing.

Plasmons in spatially separated rolled-up electron-hole double-layer systems

Using the two-component random phase approximation, we report the collective mode spectrum of a quasi-one-dimensional spatially separated electron-hole double-layer system characterized by rolled-up type-II band aligned quantum wells. We find two intra-subband collective excitations, which can be classified into optic and acoustic plasmon branches, and several inter-subband plasmon modes. At the long wavelength limit and up to a given wave vector, our model predicts and admits an undamped acoustic branch, which always lies in the gap between the intra-subband electron and hole continua, and an undamped optic branch residing within the gap between the inter-subband electron and hole continua, for all values of the electron-hole charge separations. This theoretical investigation suggests that the low-energy and Landau-undamped plasmon modes might exist based on quasi-one-dimensional, two-component spatially separated electron-hole plasmas, and their possibility could be experimentally examined.