Temperature Dependence of the Optical Response of Small Sodium Clusters

We present an analysis of the temperature dependence of the optical response of small sodium clusters in a temperature range bracketing the melting phase transition. When the temperature increases, the mean excitation energy undergoes a red shift and the plasmon is significantly broadened, in agreement with recent experimental data. We show that the single--particle levels acquire a prominent width and the HOMO--LUMO gap as well as the width of the occupied band are reduced due to large thermal cluster size and shape fluctuations. This results in a sharp increase of the static polarizability with temperature.Comment: 9 pages, Revtex, 3 uuencoded postscript figure

High-energy Landau levels in graphene beyond nearest-neighbor hopping processes: Corrections to the effective Dirac Hamiltonian

We study the Landau level spectrum of bulk graphene monolayers beyond the Dirac Hamiltonian with linear dispersion. We consider an effective Wannier-like tight-binding model obtained from ab initio calculations that includes long-range electronic hopping integral terms. We employ the Haydock-Heine-Kelly recursive method to numerically compute the Landau level spectrum of bulk graphene in the quantum Hall regime and demonstrate that this method is both accurate and computationally much faster than the standard numerical approaches used for this kind of study. The Landau level energies are also obtained analytically for an effective Hamiltonian that accounts for up to third-nearest-neighbor hopping processes. We find an excellent agreement between both approaches. We also study the effect of disorder on the electronic spectrum. Our analysis helps to elucidate the discrepancy between theory and experiment for the high-energy Landau level energies

Adiabatic Charge Pumping through Quantum Dots in the Coulomb Blockade Regime

We investigate the influence of the Coulomb interaction on the adiabatic pumping current through quantum dots. Using nonequilibrium Green's functions techniques, we derive a general expression for the current based on the instantaneous Green's function of the dot. We apply this formula to study the dependence of the charge pumped per cycle on the time-dependent pumping potentials. The possibility of charge quantization in the presence of a finite Coulomb repulsion energy is investigated in the light of recent experiments.Comment: 11 pages, 10 figure

A tight-binding model for MoS2_2 monolayers

We propose an accurate tight-binding parametrization for the band structure of MoS$_2$ monolayers near the main energy gap. We introduce a generic and straightforward derivation for the band energies equations that could be employed for other monolayer dichalcogenides. A parametrization that includes spin-orbit coupling is also provided. The proposed set of model parameters reproduce both the correct orbital compositions and location of valence and conductance band in comparison with ab initio calculations. The model gives a suitable starting point for realistic large-scale atomistic electronic transport calculations.Comment: 35 pages, 8 figure

New Aspects of Stochastic Phenomena Related to Nuclear Physics

Recent experimental results on systems where the underlying dynamics is dominated by a stochastic Hamiltonian are examined using the Random Matrix Theory (RMT). This theory is shown to be a powerful to01 in describing statistical features of quantum systems with few degrees of freedom, whose classical limit is chaotic, as well as for new facets of many-body systems at energies far above the ground state

On resumming periodic orbits in the spectra of integrable systems

Spectral determinants have proven to be valuable tools for resumming the periodic orbits in the Gutzwiller trace formula of chaotic systems. We investigate these tools in the context of integrable systems to which these techniques have not been previously applied. Our specific model is a stroboscopic map of an integrable Hamiltonian system with quadratic action dependence, for which each stage of the semiclassical approximation can be controlled. It is found that large errors occur in the semiclassical traces due to edge corrections which may be neglected if the eigenvalues are obtained by Fourier transformation over the long time dynamics. However, these errors cause serious harm to the spectral approximations of an integrable system obtained via the spectral determinants. The symmetry property of the spectral determinant does not generally alleviate the error, since it sometimes sheds a pair of eigenvalues from the unit circle. By taking into account the leading order asymptotics of the edge corrections, the spectral determinant method makes a significant recovery