20,414 research outputs found
Dirichlet's and Thomson's principles for non-selfadjoint elliptic operators with application to non-reversible metastable diffusion processes
We present two variational formulae for the capacity in the context of
non-selfadjoint elliptic operators. The minimizers of these variational
problems are expressed as solutions of boundary-value elliptic equations. We
use these principles to provide a sharp estimate for the transition times
between two different wells for non-reversible diffusion processes. This
estimate permits to describe the metastable behavior of the system
Electronic properties of correlated metals in the vicinity of a charge order transition: optical spectroscopy of -(BEDT-TTF)Hg(SCN) ( = NH, Rb, Tl)
The infrared spectra of the quasi-two-dimensional organic conductors
-(BEDT-TTF)Hg(SCN) ( = NH, Rb, Tl) were measured in
the range from 50 to 7000 \cm down to low temperatures in order to explore the
influence of electronic correlations in quarter-filled metals. The
interpretation of electronic spectra was confirmed by measurements of pressure
dependant reflectance of -(BEDT-TTF)KHg(SCN) at T=300 K. The
signatures of charge order fluctuations become more pronounced when going from
the NH salt to Rb and further to Tl compounds. On reducing the temperature,
the metallic character of the optical response in the NH and Rb salts
increases, and the effective mass diminishes. For the Tl compound, clear
signatures of charge order are found albeit the metallic properties still
dominate. From the temperature dependence of the electronic scattering rate the
crossover temperature is estimated below which the coherent charge-carriers
response sets in. The observations are in excellent agreement with recent
theoretical predictions for a quarter-filled metallic system close to charge
order
Topological phase transitions in ultra-cold Fermi superfluids: the evolution from BCS to BEC under artificial spin-orbit fields
We discuss topological phase transitions in ultra-cold Fermi superfluids
induced by interactions and artificial spin orbit fields. We construct the
phase diagram for population imbalanced systems at zero and finite
temperatures, and analyze spectroscopic and thermodynamic properties to
characterize various phase transitions. For balanced systems, the evolution
from BCS to BEC superfluids in the presence of spin-orbit effects is only a
crossover as the system remains fully gapped, even though a triplet component
of the order parameter emerges. However, for imbalanced populations, spin-orbit
fields induce a triplet component in the order parameter that produces nodes in
the quasiparticle excitation spectrum leading to bulk topological phase
transitions of the Lifshitz type. Additionally a fully gapped phase exists,
where a crossover from indirect to direct gap occurs, but a topological
transition to a gapped phase possessing Majorana fermions edge states does not
occur.Comment: With no change in text, the labels in the figures are modifie
Non-thermal origin of nonlinear transport across magnetically induced superconductor-metal-insulator transition
We have studied the effect of perpendicular magnetic fields and temperatures
on the nonlinear electronic transport in amorphous Ta superconducting thin
films. The films exhibit a magnetic field induced metallic behavior intervening
the superconductor-insulator transition in the zero temperature limit. We show
that the nonlinear transport in the superconducting and metallic phase is of
non-thermal origin and accompanies an extraordinarily long voltage response
time.Comment: 5 pages, 4 figure
Refactoring, reengineering and evolution: paths to Geant4 uncertainty quantification and performance improvement
Ongoing investigations for the improvement of Geant4 accuracy and
computational performance resulting by refactoring and reengineering parts of
the code are discussed. Issues in refactoring that are specific to the domain
of physics simulation are identified and their impact is elucidated.
Preliminary quantitative results are reported.Comment: To be published in the Proc. CHEP (Computing in High Energy Physics)
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