arXiv subjects

Gilles Montambaux

Publications and source records attributed to Gilles Montambaux.

61 records · Page 4Linked to original sources

arXiv1996

Magnetization of Mesoscopic Disordered Networks

We study the magnetic response of mesoscopic metallic isolated networks. We calculate the average and typical magnetizations in the diffusive regime for non-interacting electrons or in the first order Hartree-Fock approximation. These quantities are related to the return probability for a diffusive particle on the corresponding network. By solution of the diffusion equation on various types of networks, including a ring with arms or an infinite square network, we deduce the corresponding magnetizations. In the case of an infinite network, the Hartree-Fock average magnetization stays finite in the thermodynamic limit.

cond-mat↗

arXiv1995

What is the Thouless Energy for Ballistic Systems?

The Thouless energy, $\Ec$ characterizes numerous quantities associated with sensitivity to boundary conditions in diffusive mesoscopic conductors. What happens to these quantities if the disorder strength is decreased and a transition to the ballistic regime takes place? In the present analysis we refute the intuitively plausible assumption that $\Ec$ loses its meaning as an inverse diffusion time through the system at hand, and generally disorder independent scales take over. Instead we find that a variety of (thermodynamic) observables are still characterized by the Thouless energy.

cond-mat↗

arXiv1995

Persistent Currents for Interacting Electrons: a Simple Hartree-Fock Picture

The average persistent current of diffusive electrons in the Hartree-Fock approximation is derived in a simple non-diagrammatic picture. The Fourier expansion directly reflects the winding number decomposition of the diffusive motion around the ring. One recovers the results of Ambegaokar and Eckern, and Schmid. Moreover one finds an expression for which is valid beyond the diffusive regime.

cond-mat↗

arXiv1994

Magnetization of Disordered Ballistic Quantum Billards

We study the magnetic response of mesoscopic quantum dots in the ballistic regime where the mean free path $l_e$ is larger that the size $L$ of the sample, yet smaller than $L (k_F L)^{d-1}$. In this regime, disorder plays an important role. Employing a semiclassical picture we calculate the contribution of long trajectories which are strongly affected by static disorder and which differ sharply from those of clean systems. In the case of a magnetic field, they give rise to a large linear paramagnetic susceptibility (which is disorder independent), whose magnitude is in agreement with recent experimental results. In the case of a Aharonov-Bohm flux, the susceptibility is disorder dependent and is proportional to the mean free path as in the diffusive regime. We also discuss the corresponding non--linear susceptibilities.

cond-mat↗

arXiv1994

Universal Spectral Correlations in Diffusive Quantum Systems

We have studied numerically several statistical properties of the spectra of disordered electronic systems under the influence of an Aharonov Bohm flux $φ$, which acts as a time--reversal symmetry breaking parameter. The distribution of curvatures of the single electron energy levels has a modified Lorentz form with different exponents in the GOE and GUE regime. It has Gaussian tails in the crossover regime. The typical curvature is found to vary as $ -E_c\ln (E_cφ^2/Δ)$ ($E_c$ is the Thouless energy and $Δ$ the mean level spacing) and to diverge at zero flux. We show that the harmonics of the variation with $φ$ of single level quantities (current or curvature) are correlated, in contradiction with the perturbative result. The single level current correlation function is found to have a logarithmic behavior at low flux, in contrast to the pure symmetry cases. The distribution of single level currents is non--Gaussian in the GOE--GUE transition regime. We find a universal relation between $g_d$, the typical slope of the levels, and $g_c$, the width of the curvature distribution, as was proposed by Akkermans and Montambaux. We conjecture the validity of our results for any chaotic quantum system.

cond-mat↗

arXiv1994

Magnetic Response of Disordered Ballistic Quantum Dots

The weak field average magnetic susceptibility of square shaped mesoscopic conductors is studied within a semiclassical framework. Long semiclassical trajectories are strongly affected by static disorder and differ sharply from those of clean systems. They give rise to a large linear paramagnetic susceptibility which is disorder independent and in agreement with recent experiments. The crossover field to a nonlinear susceptibility is discussed.

cond-mat↗

arXiv1993

Poisson versus GOE statistics in integrable and non-integrable quantum hamiltonian

We calculate the level statistics by finding the eigenvalue spectrum for a variety of one-dimensional many-body models, namely the Heisenberg chain, the t-J model and the Hubbard model. In each case the generic behaviour is GOE, however at points corresponding to models known to be exactly integrable Poisson statistics are found, in agreement with an argument we outline.

cond-mat↗