2,514 research outputs found
Identifying a forward scattering superconductor through pump-probe spectroscopy
Electron-boson scattering that is peaked in the forward direction has been
suggested as an essential ingredient for enhanced superconductivity observed in
FeSe monolayers. Here, we study the superconducting state of a system dominated
by forward scattering in the time-domain and contrast its behavior against the
standard isotropic BCS case for both s- and d-wave symmetries. An analysis of
the electron's dynamics in the pump-driven non-equilibrium state reveals that
the superconducting order in the forward-focused case is robust and persistent
against the pump-induced perturbations. The superconducting order parameter
also exhibits a non-uniform melting in momentum space. We show that this
behavior is in sharp contrast to the isotropic interaction case and propose
that time-resolved approaches are a potentially powerful tool to differentiate
the nature of the dominant coupling in correlated materials.Comment: Updated the introduction and the methods section, 6 Pages, 5 figure
Theory of light-enhanced phonon-mediated superconductivity
We investigate the dynamics of a phonon-mediated superconductor driven out of
equilibrium. The electronic hopping amplitude is ramped down in time, resulting
in an increased electronic density of states. The dynamics of the coupled
electron-phonon model is investigated by solving Migdal-Eliashberg equations
for the double-time Keldysh Green's functions. The increase of the density of
states near the Fermi level leads to an enhancement of superconductivity when
the system thermalizes to the new state at the same temperature. We provide a
time- and momentum-resolved view on this thermalization process, and show that
it involves fast processes associated with single-particle scattering and much
slower dynamics associated with the superconducting order parameter. The
importance of electron-phonon coupling for the rapid enhancement and the
efficient thermalization of superconductivity is demonstrated, and the results
are compared to a BCS time-dependent mean-field approximation.Comment: 12 pages, 8 figure
General principles for the non-equilibrium relaxation of populations in quantum materials
We examine the problem of how excited populations of electrons relax after
they have been excited by a pump. We include three of the most important
relaxation processes: (i) impurity scattering; (ii) Coulomb scattering; and
(iii) electron-phonon scattering. The relaxation of an excited population of
electrons is one of the most fundamental processes measured in pump/probe
experiments, but its interpretation remains under debate. We show how several
common assumptions about non-equilibrium relaxation that are pervasive in the
field may not hold under quite general conditions. The analysis shows that
non-equilibrium relaxation is more complex than previously thought, but it
yields to recently developed theoretical methods in non-equilibrium theory. In
this work, we show how one can use many-body theory to properly interpret and
analyze these complex systems. We focus much of the discussion on implications
of these results for experiment.Comment: 13 pages, 10 figure
Crystallinity versus mass-loss rate in Asymptotic Giant Branch stars
Infrared Space Observatory (ISO) observations have shown that O-rich
Asymptotic Giant Branch (AGB) stars exhibit crystalline silicate features in
their spectra only if their mass-loss rate is higher than a certain threshold
value. Usually, this is interpreted as evidence that crystalline silicates are
not present in the dust shells of low mass-loss rate objects. In this study,
radiative transfer calculations have been performed to search for an
alternative explanation to the lack of crystalline silicate features in the
spectrum of low mass-loss rate AGB stars. It is shown that due to a temperature
difference between amorphous and crystalline silicates it is possible to
include up to 40% of crystalline silicate material in the circumstellar dust
shell, without the spectra showing the characteristic spectral features. Since
this implies that low mass-loss rate AGB stars might also form crystalline
silicates and deposit them into the Interstellar Medium (ISM), the described
observational selection effect may put the process of dust formation around AGB
stars and the composition of the predominantly amorphous dust in the
Interstellar Medium in a different light. Our model calculations result in a
diagnostic tool to determine the crystallinity of an AGB star with a known
mass-loss rate.Comment: accepted by A&A, 10 pages, 11 figure
Tunneling spectroscopy for probing orbital anisotropy in iron pnictides
Using realistic multi-orbital tight-binding Hamiltonians and the T-matrix
formalism, we explore the effects of a non-magnetic impurity on the local
density of states in Fe-based compounds. We show that scanning tunneling
spectroscopy (STS) has very specific anisotropic signatures that track the
evolution of orbital splitting (OS) and antiferromagnetic gaps. Both
anisotropies exhibit two patterns that split in energy with decreasing
temperature, but for OS these two patterns map onto each other under 90 degree
rotation. STS experiments that observe these signatures should expose the
underlying magnetic and orbital order as a function of temperature across
various phase transitions.Comment: 12 pages, 9 figures, replacement with minor changes suggested by
referee
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