2,105 research outputs found
SU(N) Fermions in a One-Dimensional Harmonic Trap
We conduct a theoretical study of SU(N) fermions confined by a
one-dimensional harmonic potential. Firstly, we introduce a new numerical
approach for solving the trapped interacting few-body problem, by which one may
obtain accurate energy spectra across the full range of interaction strengths.
In the strong-coupling limit, we map the SU(N) Hamiltonian to a spin-chain
model. We then show that an existing, extremely accurate ansatz - derived for a
Heisenberg SU(2) spin chain - is extendable to these N-component systems.
Lastly, we consider balanced SU(N) Fermi gases that have an equal number of
particles in each spin state for N=2, 3, 4. In the weak- and strong-coupling
regimes, we find that the ground-state energies rapidly converge to their
expected values in the thermodynamic limit with increasing atom number. This
suggests that the many-body energetics of N-component fermions may be
accurately inferred from the corresponding few-body systems of N
distinguishable particles.Comment: 15 pages, 6 figure
Frustrated orbital Feshbach resonances in a Fermi gas
The orbital Feshbach resonance (OFR) is a novel scheme for magnetically
tuning the interactions in closed-shell fermionic atoms. Remarkably, unlike the
Feshbach resonances in alkali atoms, the open and closed channels of the OFR
are only very weakly detuned in energy. This leads to a unique effect whereby a
medium in the closed channel can Pauli block, or frustrate, the two-body
scattering processes. Here, we theoretically investigate the impact of
frustration in the few- and many-body limits of the experimentally accessible
three-dimensional Yb system. We find that by adding a closed-channel
atom to the two-body problem, the binding energy of the ground state is
significantly suppressed, and by introducing a closed-channel Fermi sea to the
many-body problem, we can drive the system towards weaker fermion pairing.
These results are potentially relevant to superconductivity in solid-state
multiband materials, as well as to the current and continuing exploration of
unconventional Fermi-gas superfluids near the OFR.Comment: 14 pages, 6 figure
Pairing in spin polarized two-species fermionic mixtures with mass asymmetry
We discuss on the pairing mechanism of fermions with mismatch in their fermi
momenta due to a mass asymmetry. Using a variational ansatz for the ground
state we also discuss the BCS -BEC crossover of this system. It is shown that
the breached pairing solution with a single fermi surface is stable in the BEC
regime. We also include the temperatures effect on the fermion pairing within
an approximation that is valid for temperatures much below the critical
temperature.Comment: 8 pages and 6 figures, few typos corrected, version to appear in EPJ
Asymmetric Fermi superfluid with different atomic species in a harmonic trap
We study the dilute fermion gas with pairing between two species and unequal
concentrations in a harmonic trap using the mean field theory and the local
density approximation. We found that the system can exhibit a superfluid shell
structure sandwiched by the normal fermions. This superfluid shell structure
occurs if the mass ratio is larger then certain critical value which increases
from the weak-coupling BCS region to the strong-coupling BEC side. In the
strong coupling BEC regime, the radii of superfluid phase are less sensitive to
the mass ratios and are similar to the case of pairing with equal masses.
However, the lighter leftover fermions are easier to mix with the superfluid
core than the heavier ones. A partially polarized superfluid can be found if
the majority fermions are lighter, whereas phase separation is still found if
they are heavier.Comment: 12 pages, 7 figure
p-wave phase shift and scattering length of Li
We have calculated the p-wave phase shifts and scattering length of Li.
For this we solve the partial wave Schr\"odinger equation and analyze the
validity of adopting the semiclassical solution to evaluate the constant
factors in the solution. Unlike in the wave case, the semiclassical
solution does not provide unique value of the constants. We suggest an
approximate analytic solution, which provides reliable results in special
cases. Further more, we also use the variable phase method to evaluate the
phase shifts. The p-wave scattering lengths of Cs and Cs are
calculated to validate the schemes followed. Based on our calculations, the
value of the wave scattering length of Li is .Comment: 10 figure
Control of CydB and GltA1 Expression by the SenX3 RegX3 Two Component Regulatory System of Mycobacterium tuberculosis
Two component regulatory systems are used widely by bacteria to coordinate changes in global gene expression profiles in response to environmental signals. The SenX3-RegX3 two component system of Mycobacterium tuberculosis has previously been shown to play a role in virulence and phosphate-responsive control of gene expression. We demonstrate that expression of SenX3-RegX3 is controlled in response to growth conditions, although the absolute changes are small. Global gene expression profiling of a RegX3 deletion strain and wild-type strain in different culture conditions (static, microaerobic, anaerobic), as well as in an over-expressing strain identified a number of genes with changed expression patterns. Among those were genes previously identified as differentially regulated in aerobic culture, including ald (encoding alanine dehydrogenase) cyd,encoding a subunit of the cytochrome D ubiquinol oxidase, and gltA1, encoding a citrate synthase. Promoter activity in the upstream regions of both cydB and gltA1 was altered in the RegX3 deletion strain. DNA-binding assays confirmed that RegX3 binds to the promoter regions of ald, cydB and gltA1 in a phosphorylation-dependent manner. Taken together these data suggest a direct role for the SenX-RegX3 system in modulating expression of aerobic respiration, in addition to its role during phosphate limitation
Denial of long-term issues with agriculture on tropical peatlands will have devastating consequences
The BCS Functional for General Pair Interactions
The Bardeen-Cooper-Schrieffer (BCS) functional has recently received renewed
attention as a description of fermionic gases interacting with local pairwise
interactions. We present here a rigorous analysis of the BCS functional for
general pair interaction potentials. For both zero and positive temperature, we
show that the existence of a non-trivial solution of the nonlinear BCS gap
equation is equivalent to the existence of a negative eigenvalue of a certain
linear operator. From this we conclude the existence of a critical temperature
below which the BCS pairing wave function does not vanish identically. For
attractive potentials, we prove that the critical temperature is non-zero and
exponentially small in the strength of the potential.Comment: Revised Version. To appear in Commun. Math. Phys
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