2,889 research outputs found
All-optical nonequilibrium pathway to stabilizing magnetic Weyl semimetals in pyrochlore iridates
Nonequilibrium many-body dynamics is becoming one of the central topics of
modern condensed matter physics. Floquet topological states were suggested to
emerge in photodressed band structures in the presence of periodic laser
driving. Here we propose a viable nonequilibrium route without requiring
coherent Floquet states to reach the elusive magnetic Weyl semimetallic phase
in pyrochlore iridates by ultrafast modification of the effective
electron-electron interaction with short laser pulses. Combining \textit{ab
initio} calculations for a time-dependent self-consistent reduced Hubbard
controlled by laser intensity and nonequilibrium magnetism simulations for
quantum quenches, we find dynamically modified magnetic order giving rise to
transiently emerging Weyl cones that are probed by time- and angle-resolved
photoemission spectroscopy. Our work offers a unique and realistic pathway for
nonequilibrium materials engineering beyond Floquet physics to create and
sustain Weyl semimetals. This may lead to ultrafast, tens-of-femtoseconds
switching protocols for light-engineered Berry curvature in combination with
ultrafast magnetism.Comment: 27 pages including methods and supplementary information, 4 figures,
4 supplementary figure
Structure of 8B from elastic and inelastic 7Be+p scattering
Motivation: Detailed experimental knowledge of the level structure of light
weakly bound nuclei is necessary to guide the development of new theoretical
approaches that combine nuclear structure with reaction dynamics.
Purpose: The resonant structure of 8B is studied in this work.
Method: Excitation functions for elastic and inelastic 7Be+p scattering were
measured using a 7Be rare isotope beam. Excitation energies ranging between 1.6
and 3.4 MeV were investigated. An R-matrix analysis of the excitation functions
was performed.
Results: New low-lying resonances at 1.9, 2.5, and 3.3 MeV in 8B are reported
with spin-parity assignment 0+, 2+, and 1+, respectively. Comparison to the
Time Dependent Continuum Shell (TDCSM) model and ab initio no-core shell
model/resonating-group method (NCSM/RGM) calculations is performed. This work
is a more detailed analysis of the data first published as a Rapid
Communication. [J.P. Mitchell, et al, Phys. Rev. C 82, 011601(R) (2010)]
Conclusions: Identification of the 0+, 2+, 1+ states that were predicted by
some models at relatively low energy but never observed experimentally is an
important step toward understanding the structure of 8B. Their identification
was aided by having both elastic and inelastic scattering data. Direct
comparison of the cross sections and phase shifts predicted by the TDCSM and ab
initio No Core Shell Model coupled with the resonating group method is of
particular interest and provides a good test for these theoretical approaches.Comment: 15 pages, 19 figures, 3 tables, submitted to PR
Low-lying states in 8B
Excitation functions of elastic and inelastic 7Be+p scattering were measured
in the energy range between 1.6 and 2.8 MeV in the c.m. An R-matrix analysis of
the excitation functions provides strong evidence for new positive parity
states in 8B. A new 2+ state at an excitation energy of 2.55 MeV was observed
and a new 0+ state at 1.9 MeV is tentatively suggested. The R-matrix and Time
Dependent Continuum Shell Model were used in the analysis of the excitation
functions. The new results are compared to the calculations of contemporary
theoretical models.Comment: 6 pages, 5 figures, accepted as Rapid Communication in Phys. Rev.
Design and characterization of dielectric filled TM microwave cavities for ultrafast electron microscopy
Microwave cavities oscillating in the TM mode can be used as dynamic
electron-optical elements inside an electron microscope. By filling the cavity
with a dielectric material it becomes more compact and power efficient,
facilitating the implementation in an electron microscope. However, the
incorporation of the dielectric material makes the manufacturing process more
difficult. Presented here are the steps taken to characterize the dielectric
material, and to reproducibly fabricate dielectric filled cavities. Also
presented are two versions with improved capabilities. The first, called a
dual-mode cavity, is designed to support two modes simultaneously. The second
has been optimized for low power consumption. With this optimized cavity a
magnetic field strength of 2.84 0.07 mT was generated at an input power
of 14.2 0.2 W. Due to the low input powers and small dimensions, these
dielectric cavities are ideal as electron-optical elements for electron
microscopy setups
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