arXiv subjects

J. Burgdörfer

Publications and source records attributed to J. Burgdörfer.

47 records · Page 3Linked to original sources

arXiv2008

Probing Electron Correlation via Attosecond XUV Pulses in the Two-Photon Double Ionization of Helium

Recent experimental developments of high-intensity, short-pulse XUV light sources are enhancing our ability to study electron-electron correlations. We perform time-dependent calculations to investigate the so-called "sequential" regime (photon energy above 54.4 eV) in the two-photon double ionization of helium. We show that attosecond pulses allow to induce and probe angular and energy correlations of the emitted electrons. The final momentum distribution reveals regions dominated by the Wannier ridge break-up scenario and by post-collision interaction.

physics.atom-ph↗

arXiv2008

Graphene quantum dots: Beyond a Dirac billiard

We present realistic simulations of quantum confinement effects in ballistic graphene quantum dots with linear dimensions of 10 to 40 nm. We determine wavefunctions and energy level statistics in the presence of disorder resulting from edge roughness, charge impurities, or short-ranged scatterers. Marked deviations from a simple Dirac billiard for massless fermions are found. We find a remarkably stable dependence of the nearest-neighbor level spacing on edge roughness suggesting that the roughness of fabricated devices can be potentially characterized by the distribution of measured Coulomb blockade peaks.

cond-mat.mes-hall↗

arXiv2008

Nonsequential two-photon double ionization of helium

We present accurate time-dependent ab initio calculations on fully differential and total integrated (generalized) cross sections for the nonsequential two-photon double ionization of helium at photon energies from 40 to 54 eV. Our computational method is based on the solution of the time-dependent Schroedinger equation and subsequent projection of the wave function onto Coulomb waves. We compare our results with other recent calculations and discuss the emerging similarities and differences. We investigate the role of electronic correlation in the representation of the two-electron continuum states, which are used to extract the ionization yields from the fully correlated final wave function. In addition, we study the influence of the pulse length and shape on the cross sections in time-dependent calculations and address convergence issues.

physics.atom-ph↗

arXiv2007

Quantum path interference in the wavelength dependence of high-harmonic generation

We investigate the dependence of the intensity of radiation due to high-harmonic generation (HHG) as a function of the wavelength of the fundamental driver field. Superimposed on a smooth power-law dependence observed previously we find surprisingly strong and rapid fluctuations on a fine wavelength scale. We identify the origin of these fluctuations in terms of quantum path interferences with up to five returning orbits significantly contributing.

physics.atom-ph↗

arXiv2006

Nano-wires with surface disorder: Giant localization lengths and quantum-to-classical crossover

We investigate electronic quantum transport through nano-wires with one-sided surface roughness. A magnetic field perpendicular to the scattering region is shown to lead to exponentially diverging localization lengths in the quantum-to-classical crossover regime. This effect can be quantitatively accounted for by tunneling between the regular and the chaotic components of the underlying mixed classical phase space.

cond-mat.mes-hall↗

arXiv2006

Potential energy threshold for nano-hillock formation by impact of slow highly charged ions on a CaF$_2$(111) surface

We investigate the formation of nano-sized hillocks on the (111) surface of CaF$_2$ single crystals by impact of slow highly charged ions. Atomic force microscopy reveals a surprisingly sharp and well-defined threshold of potential energy carried into the collision of about 14 keV for hillock formation. Estimates of the energy density deposited suggest that the threshold is linked to a solid-liquid phase transition (``melting'') on the nanoscale. With increasing potential energy, both the basal diameter and the height of the hillocks increase. The present results reveal a remarkable similarity between the present predominantly potential-energy driven process and track formation by the thermal spike of swift ($\sim$ GeV) heavy ions.

cond-mat.other↗

arXiv2006

Transient localization in the kicked Rydberg atom

We investigate the long-time limit of quantum localization of the kicked Rydberg atom. The kicked Rydberg atom is shown to possess in addition to the quantum localization time $τ_L$ a second cross-over time $t_D$ where quantum dynamics diverges from classical dynamics towards increased instability. The quantum localization is shown to vanish as either the strength of the kicks at fixed principal quantum number or the quantum number at fixed kick strength increases. The survival probability as a function of frequency in the transient localization regime $τ_L<t<t_D$ is characterized by highly irregular, fractal-like fluctuations.

quant-ph↗

arXiv2006

Collisions of Slow Highly Charged Ions with Surfaces

Progress in the study of collisions of multiply charged ions with surfaces is reviewed with the help of a few recent examples. They range from fundamental quasi-one electron processes to highly complex ablation and material modification processes. Open questions and possible future directions will be discussed.

physics.atom-ph↗

arXiv2005

Ramsauer-Townsend Diffraction Oscillations in the Two-Dimensional Momentum Distribution of Laser-Ionized electrons

We analyze the two-dimensional momentum distribution of electrons ionized by few-cycle laser pulses in the transition regime from multiphoton absorption to tunneling by solving the time-dependent Schrödinger equation and by a classical-trajectory Monte Carlo simulation with tunneling (CTMC-T). We find a complex two-dimensional interference pattern that resembles ATI rings at higher energies and displays Ramsauer-Townsend diffraction oscillations in the angular distribution near threshold. CTMC-T calculations provide a semiclassical explanation for the dominance of selected partial waves. While the present calculation pertains to hydrogen, we find surprising qualitative agreement with recent experimental data for rare gases [1].

quant-ph↗

arXiv2003

Tunable Fano Resonances in Transport through Microwave Billiards

We present a tunable microwave scattering device that allows the controlled variation of Fano line shape parameters in transmission through quantum billiards. Transport in this device is nearly fully coherent. By comparison with quantum calculations, employing the modular recursive Green's-function method, the scattering wave function and the degree of residual decoherence can be determined. The parametric variation of Fano line shapes in terms of interacting resonances is analyzed.

cond-mat.mes-hall↗

arXiv2003

Ballistic quantum transport at high energies and high magnetic fields

We present an extension of the modular recursive Green's function method (MRGM) for ballistic quantum transport to include magnetic fields. Dividing the non-separable two-dimensional scattering problem into separable substructures allows us to calculate transport coefficients and scattering wavefunctions very efficiently. Previously unattainable energy and magnetic field regions can thereby be covered with high accuracy. The method is applied to magnetotransport through a circle and a stadium shaped quantum dot at strong magnetic fields and high energies. In the edge state regime we observe strong multi-frequency Aharonov-Bohm oscillations. By analyzing them in terms of a multi-channel interference model, we classify these fluctuations within the framework of Fano resonances and discuss their geometry independence. For high energies (mode numbers) we observe localization of the scattering wavefunction near classical trajectories.

cond-mat.mes-hall↗