506 research outputs found
Zero-temperature equation of state of mass-imbalanced resonant Fermi gases
We calculate the zero-temperature equation of state of mass-imbalanced
resonant Fermi gases in an ab initio fashion, by implementing the recent
proposal of imaginary-valued mass difference to bypass the sign problem in
lattice Monte Carlo calculations. The fully non-perturbative results thus
obtained are analytically continued to real mass imbalance to yield the
physical equation of state, providing predictions for upcoming experiments with
mass-imbalanced atomic Fermi gases. In addition, we present an exact relation
for the rate of change of the equation of state at small mass imbalances,
showing that it is fully determined by the energy of the mass-balanced system.Comment: 5 pages, 2 figures, 2 table
Inhomogeneous phases in one-dimensional mass- and spin-imbalanced Fermi gases
We compute the phase diagram of strongly interacting fermions in one
dimension at finite temperature, with mass and spin imbalance. By including the
possibility of the existence of a spatially inhomogeneous ground state, we find
regions where spatially varying superfluid phases are favored over homogeneous
phases. We obtain estimates for critical values of the temperature, mass and
spin imbalance, above which these phases disappear. Finally, we show that an
intriguing relation exists between the general structure of the phase diagram
and the binding energies of the underlying two-body bound-state problem.Comment: 5 pages, 3 figure
Phase structure of mass- and spin-imbalanced unitary Fermi gases
We study the phase diagram of mass- and spin-imbalanced unitary Fermi gases,
in search for the emergence of spatially inhomogeneous phases. To account for
fluctuation effects beyond the mean-field approximation, we employ
renormalization group techniques. We thus obtain estimates for critical values
of the temperature, mass and spin imbalance, above which the system is in the
normal phase. In the unpolarized, equal-mass limit, our result for the critical
temperature is in accordance with state-of-the-art Monte Carlo calculations. In
addition, we estimate the location of regions in the phase diagram where
inhomogeneous phases are likely to exist. We show that an intriguing relation
exists between the general structure of the many-body phase diagram and the
binding energies of the underlying two-body bound-state problem, which further
supports our findings. Our results suggest that inhomogeneous condensates form
for mass ratios of the spin-down and spin-up fermions greater than three. The
extent of the inhomogeneous phase in parameter space increases with increasing
mass imbalance.Comment: 17 pages, 7 figure
Fermi gases with imaginary mass imbalance and the sign problem in Monte Carlo calculations
Fermi gases in strongly coupled regimes, such as the unitary limit, are
inherently challenging for many-body methods. Although much progress has been
made with purely analytic methods, quantitative results require ab initio
numerical approaches, such as Monte Carlo (MC) calculations. However,
mass-imbalanced and spin-imbalanced gases are not accessible to MC calculations
due to the infamous sign problem. It was recently pointed out that the sign
problem, for finite spin imbalance, can be circumvented by resorting to
imaginary polarizations and analytic continuation. Large parts of the phase
diagram spanned by temperature and polarization then become accessible to MC
calculations. We propose to apply a similar strategy to the mass-imbalanced
case, which opens up the possibility to study the associated phase diagram with
MC calculations. In particular, our analysis suggests that a detection of a
(tri-)critical point in this phase diagram is possible. We also discuss
calculations in the zero-temperature limit with our approach.Comment: 5 pages, 3 figure
Phases of spin- and mass-imbalanced ultracold Fermi gases in harmonic traps
We analyze the phase structure of mass- and spin-imbalanced unitary Fermi
gases in harmonic traps. To this end, we employ Density Functional Theory in
the local density approximation. Depending on the values of the control
parameters measuring mass and spin imbalance, we observe that three regions
exist in the trap, namely: a superfluid region at the center, surrounded by a
mixed region of resonantly interacting spin-up and spin-down fermions, and
finally a fully polarized phase surrounding the previous two regions. We also
find regimes in the phase diagram where the existence of a superfluid region at
the center of the trap is not energetically favored. We point out the
limitations of our approach at the present stage, and call for more detailed
(ab initio) studies of the equation of state of uniform, mass-imbalanced
unitary Fermi gases.Comment: 10 pages, 7 figure
Recent advances in the simulation of particle-laden flows
A substantial number of algorithms exists for the simulation of moving
particles suspended in fluids. However, finding the best method to address a
particular physical problem is often highly non-trivial and depends on the
properties of the particles and the involved fluid(s) together. In this report
we provide a short overview on a number of existing simulation methods and
provide two state of the art examples in more detail. In both cases, the
particles are described using a Discrete Element Method (DEM). The DEM solver
is usually coupled to a fluid-solver, which can be classified as grid-based or
mesh-free (one example for each is given). Fluid solvers feature different
resolutions relative to the particle size and separation. First, a
multicomponent lattice Boltzmann algorithm (mesh-based and with rather fine
resolution) is presented to study the behavior of particle stabilized fluid
interfaces and second, a Smoothed Particle Hydrodynamics implementation
(mesh-free, meso-scale resolution, similar to the particle size) is introduced
to highlight a new player in the field, which is expected to be particularly
suited for flows including free surfaces.Comment: 16 pages, 4 figure
Zero-Temperature Equation of State of Mass-Imbalanced Resonant Fermi Gases
We calculate the zero-temperature equation of state of mass-imbalanced resonant Fermi gases in an ab initio fashion, by implementing the recent proposal of imaginary-valued mass difference to bypass the sign problem in lattice Monte Carlo calculations. The fully non-perturbative results thus obtained are analytically continued to real mass imbalance to yield the physical equation of state, providing predictions for upcoming experiments with mass-imbalanced atomic Fermi gases. In addition, we present an exact relation for the rate of change of the equation of state at small mass imbalances, showing that it is fully determined by the energy of the mass-balanced system
Lava channel formation during the 2001 eruption on Mount Etna: evidence for mechanical erosion
We report the direct observation of a peculiar lava channel that was formed
near the base of a parasitic cone during the 2001 eruption on Mount Etna.
Erosive processes by flowing lava are commonly attributed to thermal erosion.
However, field evidence strongly suggests that models of thermal erosion cannot
explain the formation of this channel. Here, we put forward the idea that the
essential erosion mechanism was abrasive wear. By applying a simple model from
tribology we demonstrate that the available data agree favorably with our
hypothesis. Consequently, we propose that erosional processes resembling the
wear phenomena in glacial erosion are possible in a volcanic environment.Comment: accepted for publication in Physical Review Letter
Thermal equation of state of polarized fermions in one dimension via complex chemical potentials
We present a nonperturbative computation of the equation of state of polarized, attractively interacting, nonrelativistic fermions in one spatial dimension at finite temperature. We show results for the density, spin magnetization, magnetic susceptibility, and Tan's contact. We compare with the second-order virial expansion, a next-to-leading-order lattice perturbation theory calculation, and interpret our results in terms of pairing correlations. Our lattice Monte Carlo calculations implement an imaginary chemical potential difference to avoid the sign problem. The thermodynamic results on the imaginary side are analytically continued to obtain results on the real axis. We focus on an intermediate- to strong-coupling regime, and cover a wide range of temperatures and spin imbalances
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