Propagation Of Electron Wave Packets Research Articles

Local and Nonlocal Electron Dynamics of Au/Fe/MgO(001) Heterostructures Analyzed by Time-Resolved Two-Photon Photoemission Spectroscopy.

Employing femtosecond laser pulses in front and back side pumping of Au/Fe/MgO(001) combined with detection in two-photon photoelectron emission spectroscopy, we analyze local relaxation dynamics of excited electrons in buried Fe, injection into Au across the Fe-Au interface, and electron transport across the Au layer at 0.6 to 2.0eV above the Fermi energy. By analysis as a function of Au film thickness we obtain the electron lifetimes of bulk Au and Fe and distinguish the relaxation in the heterostructure's constituents. We also show that the excited electrons propagate through Au in a superdiffusive regime and conclude further that electron injection across the epitaxial interface proceeds ballistically by electron wave packet propagation.

Erratum: Photoionization of hydrogen atoms by coherent intense high-frequency short laser pulses: Direct propagation of electron wave packets on large spatial grids [Phys. Rev. A 88 , 023422 (2013)

Erratum: Photoionization of hydrogen atoms by coherent intense high-frequency short laser pulses: Direct propagation of electron wave packets on large spatial grids [Phys. Rev. A <b>88</b> , 023422 (2013)

Dispersionless propagation of electron wavepackets in single-walled carbon nanotubes

We investigate the propagation of electron wavepackets in single-walled carbon nanotubes via a Lindblad-based density-matrix approach that enables us to account for both dissipation and decoherence effects induced by various phonon modes. We show that, while in semiconducting nanotubes the wavepacket experiences the typical dispersion of conventional materials, in metallic nanotubes its shape remains essentially unaltered, even in the presence of the electron-phonon coupling, up to micron distances at room temperature.

Direct observation of electron propagation and dielectric screening on the atomic length scale.

The propagation and transport of electrons in crystals is a fundamental process pertaining to the functioning of most electronic devices. Microscopic theories describe this phenomenon as being based on the motion of Bloch wave packets. These wave packets are superpositions of individual Bloch states with the group velocity determined by the dispersion of the electronic band structure near the central wavevector in momentum space. This concept has been verified experimentally in artificial superlattices by the observation of Bloch oscillations--periodic oscillations of electrons in real and momentum space. Here we present a direct observation of electron wave packet motion in a real-space and real-time experiment, on length and time scales shorter than the Bloch oscillation amplitude and period. We show that attosecond metrology (1 as = 10(-18) seconds) now enables quantitative insight into weakly disturbed electron wave packet propagation on the atomic length scale without being hampered by scattering effects, which inevitably occur over macroscopic propagation length scales. We use sub-femtosecond (less than 10(-15) seconds) extreme-ultraviolet light pulses to launch photoelectron wave packets inside a tungsten crystal that is covered by magnesium films of varied, well-defined thicknesses of a few ångströms. Probing the moment of arrival of the wave packets at the surface with attosecond precision reveals free-electron-like, ballistic propagation behaviour inside the magnesium adlayer--constituting the semi-classical limit of Bloch wave packet motion. Real-time access to electron transport through atomic layers and interfaces promises unprecedented insight into phenomena that may enable the scaling of electronic and photonic circuits to atomic dimensions. In addition, this experiment allows us to determine the penetration depth of electrical fields at optical frequencies at solid interfaces on the atomic scale.

Photoionization of hydrogen atoms by coherent intense high-frequency short laser pulses: Direct propagation of electron wave packets on large spatial grids

The time-dependent Schr\"{o}dinger equation for the hydrogen atom and its interaction with coherent intense high-frequency short laser pulses is solved numerically exactly by propagating the single-electron wave packets. Thereby, the wavefunction is followed in space and time for times longer than the pulse duration. Results are explicitly shown for 3 and 10 fs pulses. Particular attention is paid to identifying the effect of dynamic interference of photoelectrons emitted with the same kinetic energy at different times during the rising and falling sides of the pulse predicted in [\emph{Ph.V. Demekhin and L.S. Cederbaum}, Phys. Rev. Lett. \textbf{108}, 253001 (2012)]. In order to be able to see the dynamic interference pattern in the computed electron spectra, the photoelectron wave packet has to be propagated over long distances. Clearly, complex absorption potentials often employed to compute spectra of emitted particles cannot be used to detect dynamic interference. For the considered high-frequency pulses of 3 and 10 fs durations, this requires enormously large spatial grids. The presently computed photoionization and above-threshold ionization spectra are found to exhibit pronounced dynamic interference patterns. Where available, the patterns are in very good agreement with previously published results on the photoionization spectra which have been computed using a completely different method, thus supporting the previously made assumption that the above-threshold ionization processes are very weak for the considered pulse intensities and high carrier frequency. The quiver motion in space and time of a free electron in strong laser pulses is also investigated numerically. Finally, a discussion is presented of how fast the atom is ionized by an intense pulse.

Communication: Phase space approach to laser-driven electronic wavepacket propagation

We propose a phase space method to propagate a quantum wavepacket driven by a strong external field. The method employs the periodic von Neumann basis with biorthogonal exchange recently introduced for the calculation of the energy eigenstates of time-independent quantum systems [A. Shimshovitz and D. J. Tannor, Phys. Rev. Lett. (in press) [e-print arXiv:1201.2299v1]]. While the individual elements in this basis set are time-independent, a small subset is chosen in a time-dependent manner to adapt to the evolution of the wavepacket in phase space. We demonstrate the accuracy and efficiency of the present propagation method by calculating the electronic wavepacket in a one-dimensional soft-core atom interacting with a superposition of an intense, few-cycle, near-infrared laser pulse and an attosecond extreme-ultraviolet laser pulse.

Electron wavepacket propagation in a chain of coupled quantum dots

We study the coherent dynamics of one- and two-electron transport in a linear array oftunnel-coupled quantum dots. We find that this system exhibits a rich variety of coherentphenomena, ranging from electron wavepacket propagation and interference totwo-particle bonding and entanglement. Our studies, apart from their relevanceto the exploration of quantum dynamics and transport in periodic structures,are also aimed at possible applications in future quantum computation schemes.

The electron wave packet propagation in ZnS/ZnSe based effective-mass quantum well structure: application of the Chebishev method and fast Hanckel transform

The evolution of a cylindrically symmetric 3D electron wave packet, normally incident on interface planes of a ZnS/ZnSe effective mass quantum well structure, is studied using the Chebishev propagation scheme. Due to the symmetry of the problem, the fast Hanckel transform and fast Fourier transform were employed in calculations of the kinetic energy part of the Hamiltonian. Numerical results show that the structure is highly transmissive, related to the lack of the built-in potential at the interfaces, but that the effective mass mismatch induces some changes in the wave packet not seen in the conventional resonant tunneling structures. Also given, in the Appendix, is an improved accuracy fast Hanckel transform algorithm.

Investigation of time-dependent resonant interband tunneling

We present a time-dependent calculation of InAs/AlSb/GaSb/AlSb/InAs and InAs/GaSb/InAs resonant interband tunneling structures. We follow the propagation of electron wave packets through the systems and determine the temporal behavior of the device operation by calculating various time scales. We compare these time scales with the lifetime of the corresponding quasi-bound state computed from both the static transmission curve and the exact solution of the quasi-bound state.

Time-dependent transport in two-dimensional quantum-wire structures.

We present a time-dependent calculation of electron transport in two-dimensional quantum-wire-based devices: the electron waveguide coupler, the quantum modulated transistor, and a quantum wire with a narrow double constriction. We follow the propagation of electron wave packets through the systems and determine the temporal behavior of the device operation by calculating various time scales