73,590 research outputs found
Tunable subpicosecond electron bunch train generation using a transverse-to-longitudinal phase space exchange technique
We report on the experimental generation of a train of subpicosecond electron
bunches. The bunch train generation is accomplished using a beamline capable of
exchanging the coordinates between the horizontal and longitudinal degrees of
freedom. An initial beam consisting of a set of horizontally-separated beamlets
is converted into a train of bunches temporally separated with tunable bunch
duration and separation. The experiment reported in this Letter unambiguously
demonstrates the conversion process and its versatility.Comment: 4 pages, 5 figures, 1 table; accepted for publication in PR
The Suppression and Recovery of the Ferroelectric Phase in Multiferroic
We report the discovery of a complete suppression of ferroelectricity in
by 10 % iron substitution and its restoration in external magnetic
fields. The spontaneous polarization in arises below 12
K in external fields above 4 T. The magnetic/ferroelectric phase diagram is
constructed from the anomalies of the dielectric constant, polarization,
magnetization, and heat capacity. The observations are qualitatively described
by a mean field model with competing interactions and strong anisotropy. We
propose that the magnetic field induces a non-collinear inversion symmetry
breaking magnetic structure in
Line nodes in the superconducting gap function of noncentrosymmetric CePt_3Si
The superconducting gap structure of recently discovered heavy fermion
CePt_3Si without spatial inversion symmetry was investigated by thermal
transport measurements down to 40 mK. In zero field a residual T-linear term
was clearly resolved as T-> 0, with a magnitude in good agreement with the
value expected for a residual normal fluid with a nodal gap structure, together
with a T^2-dependence at high temperatures. With an applied magnetic fields,
the thermal conductivity grows rapidly, in dramatic contrast to fully gapped
superconductors, and exhibits one-parameter scaling with T/sqrt{H}. These
results place an important constraint on the order parameter symmetry, that is
CePt_3Si is most likely to have line nodes.Comment: 5pages, 3figures, accpted for publication in Phys. Rev. Let
Formation and Acceleration of Uniformly-Filled Ellipsoidal Electron Bunches Obtained via Space-Charge-Driven Expansion from a Cesium-Telluride Photocathode
We report the experimental generation, acceleration and characterization of a
uniformly-filled electron bunch obtained via space-charge-driven expansion
(often referred to as "blow-out regime") in an L-band (1.3-GHz) radiofrequency
photoinjector. The beam is photoemitted from a Cesium-Telluride semiconductor
photocathode using a short ( fs) ultraviolet laser pulse. The produced
electron bunches are characterized with conventional diagnostics and the
signatures of their ellipsoidal character is observed. We especially
demonstrate the production of ellipsoidal bunches with charges up to
nC corresponding to a -fold increase compared to previous experiments
with metallic photocathodes.Comment: 9, pages, 13 figure
Superdeformed Band in ^{36}Ar Described by Projected Shell Model
The projected shell model implements shell model configuration mixing in the
projected deformed basis. Our analysis on the recently observed superdeformed
band in Ar suggests that the neutron and proton 2-quasiparticle and the
4-quasiparticle bands cross the superdeformed ground band at the same angular
momentum. This constitutes a picture of band disturbance in which the first and
the second band-crossing, commonly seen at separate rotation frequencies in
heavy nuclei, occur simultaneously. We also attempt to understand the
assumptions of two previous theoretical calculations which interpreted this
band. Electromagnetic properties of the band are predicted.Comment: 4 pages and 2 figures, accepted by Phys. Rev. C as a Rapid
Communicatio
Experimental evidence for a two-gap structure of superconducting NbSe_2: a specific heat study in external magnetic fields
To resolve the discrepancies of the superconducting order parameter in
quasi-two-dimensional NbSe_2, comprehensive specific-heat measurements have
been carried out. By analyzing both the zero-field and mixed-state data with
magnetic fields perpendicular to and parallel to the c axis of the crystal and
using the two-gap model, we conclude that (1) more than one energy scale of the
order parameter is required for superconducting NbSe_2 due to the thermodynamic
consistency; (2)delta_L=1.26 meV and delta_S=0.73 meV are obtained; (3)
N_S(0)/N(0)=11%~20%; (4) The observation of the kink in gamma(H) curve suggests
that the two-gap scenario is more favorable than the anisotropic s-wave model
to describe the gap structure of NbSe_2; and (5)delta_S is more isotropic and
has a three-dimensional-like feature and is located either on the Se or the
bonding Nb Fermi sheets.Comment: 16 pages, 4 figure
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