Quantum dot dephasing by edge states

We calculate the dephasing rate of an electron state in a pinched quantum dot, due to Coulomb interactions between the electron in the dot and electrons in a nearby voltage biased ballistic nanostructure. The dephasing is caused by nonequilibrium time fluctuations of the electron density in the nanostructure, which create random electric fields in the dot. As a result, the electron level in the dot fluctuates in time, and the coherent part of the resonant transmission through the dot is suppressed

Giant isotope effect in the incoherent tunneling specific heat of the molecular nanomagnet Fe8

Time-dependent specific heat experiments on the molecular nanomagnet Fe8 and the isotopic enriched analogue 57Fe8 are presented. The inclusion of the 57Fe nuclear spins leads to a huge enhancement of the specific heat below 1 K, ascribed to a strong increase in the spin-lattice relaxation rate Gamma arising from incoherent, nuclear-spin-mediated magnetic quantum tunneling in the ground-doublet. Since Gamma is found comparable to the expected tunneling rate, the latter process has to be inelastic. A model for the coupling of the tunneling levels to the lattice is presented. Under transverse field, a crossover from nuclear-spin-mediated to phonon-induced tunneling is observed.Comment: Replaced with version accepted for publication in Physical Review Letter

Diffuse emission in the presence of inhomogeneous spin-orbit interaction for the purpose of spin filtration

A lateral interface connecting two regions with different strengths of the Bychkov-Rashba spin-orbit interaction can be used as a spin polarizer of electrons in two dimensional semiconductor heterostructures. [Khodas \emph{et al.}, Phys. Rev. Lett. \textbf{92}, 086602 (2004)]. In this paper we consider the case when one of the two regions is ballistic, while the other one is diffusive. We generalize the technique developed for the solution of the problem of the diffuse emission to the case of the spin dependent scattering at the interface, and determine the distribution of electrons emitted from the diffusive region. It is shown that the diffuse emission is an effective way to get electrons propagating at small angles to the interface that are most appropriate for the spin filtration and a subsequent spin manipulation. Finally, a scheme is proposed of a spin filter device, see Fig. 9, that creates two almost fully spin-polarized beams of electrons.Comment: 11 pages, 9 figure

Cosmic-ray electron injection from the ionization of nuclei

We show that the secondary electrons ejected from the ionization of heavy ions can be injected into the acceleration process that occurs at supernova remnant shocks. This electron injection mechanism works since ions are ionized during the acceleration when they move already with relativistic speed, just like ejected electrons do. Using the abundances of heavy nuclei measured in cosmic rays at Earth, we estimate the electron/proton ratio at the source to be ~10^-4, big enough to account for the nonthermal synchrotron emission observed in young SNRs. We also show that the ionization process can limit the maximum energy that heavy ions can reach.Comment: 4 pages, 1 figure, accepted for publication in Physical Review Letter

Levinson theorem for Aharonov-Bohm scattering in two dimensions

We apply the recently generalized Levinson theorem for potentials with inverse square singularities [Sheka et al, Phys.Rev.A, v.68, 012707 (2003)] to Aharonov-Bohm systems in two-dimensions. By this theorem, the number of bound states in a given m-th partial wave is related to the phase shift and the magnetic flux. The results are applied to 2D soliton-magnon scattering.Comment: 5 pages (REVTeX

Acoustoelectric current and pumping in a ballistic quantum point contact

The acoustoelectric current induced by a surface acoustic wave (SAW) in a ballistic quantum point contact is considered using a quantum approach. We find that the current is of the "pumping" type and is not related to drag, i.e. to the momentum transfer from the wave to the electron gas. At gate voltages corresponding to the plateaus of the quantized conductance the current is small. It is peaked at the conductance step voltages. The peak current oscillates and decays with increasing SAW wavenumber for short wavelengths. These results contradict previous calculations, based on the classical Boltzmann equation.Comment: 4 pages, 1 figur

Effect of Interactions on the Admittance of Ballistic Wires

A self-consistent theory of the admittance of a perfect ballistic, locally charge neutral wire is proposed. Compared to a non-interacting theory, screening effects drastically change the frequency behavior of the conductance. In the single-channel case the frequency dependence of the admittance is monotonic, while for two or more channels collective interchannel excitations lead to resonant structures in the admittance. The imaginary part of the admittance is typically positive, but can become negative near resonances.Comment: Presentation considerably modified; the results are unchanged. 4 pages, 2 figures .eps-format include

Probing Micro-quasars with TeV Neutrinos

The jets associated with Galactic micro-quasars are believed to be ejected by accreting stellar mass black-holes or neutron stars. We show that if the energy content of the jets in the transient sources is dominated by electron-proton plasma, then a several hour outburst of 1--100 TeV neutrinos produced by photo- meson interactions should precede the radio flares associated with major ejection events. Several neutrinos may be detected during a single outburst by a 1km^2 detector, thereby providing a powerful probe of micro-quasars jet physics.Comment: Accepted to PRL. More detailed discussion of particle acceleratio

Induced scattering of short radio pulses

Effect of the induced Compton and Raman scattering on short, bright radio pulses is investigated. It is shown that when a single pulse propagates through the scattering medium, the effective optical depth is determined by the duration of the pulse but not by the scale of the medium. The induced scattering could hinder propagation of the radio pulse only if close enough to the source a dense enough plasma is presented. The induced scattering within the relativistically moving source places lower limits on the Lorentz factor of the source. The results are applied to the recently discovered short extragalactic radio pulse.Comment: submitted to Ap

A Mesoscopic Quantum Eraser

Motivated by a recent experiment by Buks et al. [Nature 391, 871 (1998)] we consider electron transport through an Aharonov-Bohm interferometer with a quantum dot in one of its arms. The quantum dot is coupled to a quantum system with a finite number of states acting as a which-path detector. The Aharonov-Bohm interference is calculated using a two-particle scattering approach for the joint transitions in detector and quantum dot. Tracing over the detector yields dephasing and a reduction of the interference amplitude. We show that the interference can be restored by a suitable measurement on the detector and propose a mesoscopic quantum eraser based on this principle.Comment: 7 pages, 2 figures, to appear in Europhys. Lett., uses EuroPhys.sty and EuroMacro.tex (included