8,519 research outputs found
Macroscopic coherence effects in a mesoscopic system: Weak localization of thin silver films in an undergraduate lab
We present an undergraduate lab that investigates weak localization in thin
silver films. The films prepared in our lab have thickness, , between 60-200
\AA, a mesoscopic length scale. At low temperatures, the inelastic dephasing
length for electrons, , exceeds the thickness of the film (), and the films are then quasi-2D in nature. In this situation, theory
predicts specific corrections to the Drude conductivity due to coherent
interference between conducting electrons' wavefunctions, a macroscopically
observable effect known as weak localization. This correction can be destroyed
with the application of a magnetic field, and the resulting magnetoresistance
curve provides information about electron transport in the film. This lab is
suitable for Junior or Senior level students in an advanced undergraduate lab
course.Comment: 16 pages, 9 figures. Replaces earlier version of paper rejected by
Am. J. Phys. because of too much content on vacuum systems. New version deals
with the undergraduate experiment on weak localization onl
The JKind Model Checker
JKind is an open-source industrial model checker developed by Rockwell
Collins and the University of Minnesota. JKind uses multiple parallel engines
to prove or falsify safety properties of infinite state models. It is portable,
easy to install, performance competitive with other state-of-the-art model
checkers, and has features designed to improve the results presented to users:
inductive validity cores for proofs and counterexample smoothing for test-case
generation. It serves as the back-end for various industrial applications.Comment: CAV 201
Medium corrections in the formation of light charged particles in heavy ion reactions
Within a microscopic statistical description of heavy ion collisions, we
investigate the effect of the medium on the formation of light clusters. The
dominant medium effects are self-energy corrections and Pauli blocking that
produce the Mott effect for composite particles and enhanced reaction rates in
the collision integrals. Microscopic description of composites in the medium
follows the Dyson equation approach combined with the cluster mean-field
expansion. The resulting effective few-body problem is solved within a properly
modified Alt-Grassberger-Sandhas formalism. The results are incorporated in a
Boltzmann-Uehling-Uhlenbeck simulation for heavy ion collisions. The number and
spectra of light charged particles emerging from a heavy ion collision changes
in a significant manner in effect of the medium modification of production and
absorption processes.Comment: 16 pages, 6 figure
Investigations of solutions of Einstein's field equations close to lambda-Taub-NUT
We present investigations of a class of solutions of Einstein's field
equations close to the family of lambda-Taub-NUT spacetimes. The studies are
done using a numerical code introduced by the author elsewhere. One of the main
technical complication is due to the S3-topology of the Cauchy surfaces.
Complementing these numerical results with heuristic arguments, we are able to
yield some first insights into the strong cosmic censorship issue and the
conjectures by Belinskii, Khalatnikov, and Lifschitz in this class of
spacetimes. In particular, the current investigations suggest that strong
cosmic censorship holds in this class. We further identify open issues in our
current approach and point to future research projects.Comment: 24 pages, 12 figures, uses psfrag and hyperref; replaced with
published version, only minor corrections of typos and reference
Observation of vortices and hidden pseudogap from scanning tunneling spectroscopic studies of electron-doped cuprate superconductor
We present the first demonstration of vortices in an electron-type cuprate
superconductor, the highest (= 43 K) electron-type cuprate
. Our spatially resolved quasiparticle tunneling spectra
reveal a hidden low-energy pseudogap inside the vortex core and unconventional
spectral evolution with temperature and magnetic field. These results cannot be
easily explained by the scenario of pure superconductivity in the ground state
of high- superconductivity.Comment: 6 pages, 4 figures. Two new graphs have been added into Figure 2.
Accepted for publication in Europhysics Letters. Corresponding author:
Nai-Chang Yeh (E-mail: [email protected]
Dynamics of photoinduced Charge Density Wave-metal phase transition in K0.3MoO3
We present first systematic studies of the photoinduced phase transition from
the ground charge density wave (CDW) state to the normal metallic (M) state in
the prototype quasi-1D CDW system K0.3MoO3. Ultrafast non-thermal CDW melting
is achieved at the absorbed energy density that corresponds to the electronic
energy difference between the metallic and CDW states. The results imply that
on the sub-picosecond timescale when melting and subsequent initial recovery of
the electronic order takes place the lattice remains unperturbed.Comment: Phys. Rev. Lett., accepted for publicatio
Black-body radiation induced photodissociation and population redistribution of weakly bound states in H
Molecular hydrogen ions in weakly bound states close to the first
dissociation threshold are attractive quantum sensors for measuring the
proton-to-electron mass ratio and hyperfine-induced ortho-para mixing. The
experimental accuracy of previous spectroscopic studies relying on fast ion
beams could be improved by using state-of-the-art ion trap setups. With the
electric dipole moment vanishing in H and preventing fast spontaneous
emission, radiative lifetimes of the order of weeks are found. We include the
effect of black-body radiation that can lead to photodissociation and
rovibronic state redistribution to obtain effective lifetimes for trapped ion
experiments. Rate coefficients for bound-bound and bound-continuum processes
were calculated using adiabatic nuclear wave functions and nonadiabatic
energies, including relativistic and radiative corrections. Effective lifetimes
for the weakly bound states were obtained by solving a rate equation model and
lifetimes in the range of 4 to 523~ms and 215~ms were found at room
temperature and liquid nitrogen temperature, respectively. Black-body induced
photodissociation was identified as the lifetime-limiting effect, which
guarantees the purity of state-selectively generated molecular ion ensembles.
The role of hyperfine-induced -mixing, which allows pure rovibrational
transitions, was found to be negligible.Comment: 13 pages, 5 figure
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