Microbunching And Coherent Acceleration Of Electrons By Subcycle Laser Pulses

The pick up and acceleration of all plasma electrons irradiated by an intense, subcyclic laser pulse is demonstrated via analytical and numerical calculations. It is shown that the initial low emittance of the plasma electrons is conserved during the process of acceleration, leading to an extremely cold, bunched electron beam. Compression of the electron bunch along the longitudinal coordinate is naturally achieved due to the interaction of electrons and laser pulse. In this paper, we find the localized solutions to Maxwell's equations of a subcyclic laser pulse and use these to determine the acceleration of charged particles and we suggest future application for this acceleration mechanism as low energy particle injector and as electron source for coherent x-ray generation.Physic

Canonical-basis solution of the Hartree-Fock-Bogoliubov equation on three-dimensional Cartesian mesh

A method is presented to obtain the canonical-form solutions of the HFB equation for atomic nuclei with zero-range interactions like the Skyrme force. It is appropriate to describe pairing correlations in the continuum in coordinate-space representations. An improved gradient method is used for faster convergences under constraint of orthogonality between orbitals. To prevent high-lying orbitals to shrink into a spatial point, a repulsive momentum dependent force is introduced, which turns out to unveil the nature of high-lying canonical-basis orbitals. The asymptotic properties at large radius and the relation with quasiparticle states are discussed for the obtained canonical basis.Comment: 23 pages including 17 figures, REVTeX4, revised version, scheduled to appear in Phys. Rev. C, Vol.69, No.

Comment on ''Phase Diagram of La2−x_{2-x}Srx_xCuO4_4 Probed in the Infrared: Imprints of Charge Stripe Excitations''

Recently Lucarelli {\it et al.} have reported\cite{lucarelli} temperature-dependence of the in-plane optical reflectivity of La$_{2-x}$Sr$_x$CuO$_4$ over a wide doping range, focusing on the infrared peaks at 30 cm$^{-1}$ (for $x$=0.12), 250 cm$^{-1}$ and 510 cm$^{-1}$. They interpreted the first peak (30 cm$^{-1}$) as a signature of charge stripe ordering, while the latter two (250 cm$^{-1}$ and 510 cm$^{-1}$) are attributed to the polaronic charge excitations. However, careful readers would notice that the reported spectra are largely different from those so far measured on the same system. As we illustrate below, all these peaks are caused by an uncontrolled leakage of the c-axis reflectivity into the measured spectra.Comment: 1 page, 1 figure, accepted for publication in Phys. Rev. Lett 91 (2003

Possible Verification of Tilted Anisotropic Dirac Cone in \alpha-(BEDT-TTF)_2 I_3 Using Interlayer Magnetoresistance

It is proposed that the presence of a tilted and anisotropic Dirac cone can be verified using the interlayer magnetoresistance in the layered Dirac fermion system, which is realized in quasi-two-dimensional organic compound \alpha-(BEDT-TTF)_2 I_3. Theoretical formula is derived using the analytic Landau level wave functions and assuming local tunneling of electrons. It is shown that the resistivity takes the maximum in the direction of the tilt if anisotropy of the Fermi velocity of the Dirac cone is small. The procedure is described to determine the parameters of the tilt and anisotropy.Comment: 4 pages, 4 figures, corrected Fig.

In-plane optical conductivity of La2−x_{2-x}Srx_xCuO4_4: Reduced superconducting condensate and residual Drude-like response

Temperature dependences of the optical spectra of La$_{2-x}$Sr$_x$CuO$_4$ with $x$=0.12 and 0.15 were carefully examined for a polarization parallel to the CuO$_2$-plane over a wide frequency range down to 8 cm$^{-1}$. Selection of well-characterized crystals enabled us to measure purely in-plane polarized spectra without any additional peak. The weight of superconducting (SC) condensate estimated from the missing area in $\sigma_1(\omega$) well agrees with the estimate from the slope of $\sigma_2(\omega$) vs 1/$\omega$ plot, showing no evidence that the Ferrell-Glover-Tinkham sum-rule is violated in the optical spectrum. We demonstrate that the optically estimated SC condensate is much smaller than the value obtained from the $\mu$SR measurement of magnetic penetration depth. We also find an anomalous increase of conductivity in sub-millimeter region towards $\omega$=0 below $T_c$, which suggests the microscopic inhomogeneity in the superconducting state. Both observations are discussed in relation with the inhomogeneous electronic state that might be inherent to high-$T_c$ cuprates.Comment: 10 pages, 6 figure

The vortex depinning transition in untwinned YBaCuO using complex impedance measurements

We present surface impedance measurement of the vortex linear response in a large untwinned YBCO crystal. The depinning spectra obtained over a broad frequency range (100 Hz- 30 MHz) are those of a surface pinned vortex lattice with a free flux flow resistivity (two modes response). The critical current in the "Campbell" like regime and the flux flow resistivity in the dissipative regime are extracted. Those two parameters are affected by the first order transition, showing that this transition may be related to the electronic state of vortices.Comment: to be published in the proceedings of M2S RI

Electrodynamics of the vortex lattice in untwinned YBaCuO by complex impedance measurements

We report complex impedance measurements in an untwinned YBaCuO crystal. Our broad frequency range covers both the quasi static response and the resistive response of the vortex lattice. It allow us to characterize the irreversibility line without the need of any frequency dependent pinning parameters. We confirm the validity of the two modes model of vortex dynamic, and extract both the surface critical current and the flux flow resistivity around the first order transition $T_{m}$. This latter is identified by the abrupt loss of pinning and by an unexpected step of $\rho_{ff}(T)$ at $T_{m}$.Comment: accepted for publication in EPJ

Charge Ordering in alpha-(BEDT-TTF)2I3 by synchrotron x-ray diffraction

The spatial charge arrangement of a typical quasi-two-dimensional organic conductor alpha-(BEDT-TTF)2I3 is revealed by single crystal structure analysis using synchrotron radiation. The results show that the horizontal stripe type structure, which was suggested by mean field theory, is established. We also find the charge disproportion above the metal-insulator transition temperature and a significant change in transfer integrals caused by the phase transition. Our result elucidates the insulating phase of this material as a 2k_F charge density localization.Comment: 8 pages, 5 figures, 1 tabl

Laser-driven collimated tens-GeV monoenergetic protons from mass-limited target plus preformed channel

Proton acceleration by ultra-intense laser pulse irradiating a target with cross-section smaller than the laser spot size and connected to a parabolic density channel is investigated. The target splits the laser into two parallel propagating parts, which snowplow the back-side plasma electrons along their paths, creating two adjacent parallel wakes and an intense return current in the gap between them. The radiation-pressure pre-accelerated target protons trapped in the wake fields now undergo acceleration as well as collimation by the quasistatic wake electrostatic and magnetic fields. Particle-in-cell simulations show that stable long-distance acceleration can be realized, and a 30 fs monoenergetic ion beam of >10 GeV peak energy and <2 degrees divergence can be produced by a circularly polarized laser pulse at an intensity of about 10(22) W/cm(2). (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4775728]Physics, Fluids & PlasmasSCI(E)EI3ARTICLE1null2