966 research outputs found
Topological superfluid phases of an atomic Fermi gas with in- and out-of-plane Zeeman fields and equal Rashba-Dresselhaus spin-orbit coupling
We analyze the effects of in- and out-of-plane Zeeman fields on the BCS-BEC
evolution of a Fermi gas with equal Rashba-Dresselhaus (ERD) spin-orbit
coupling (SOC). We show that the ground state of the system involves novel
gapless superfluid phases that can be distinguished with respect to the
topology of the momentum-space regions with zero excitation energy. For the
BCS-like uniform superfluid phases with zero center-of-mass momentum, the zeros
may correspond to one or two doubly-degenerate spheres, two or four spheres,
two or four concave spheroids, or one or two doubly-degenerate circles,
depending on the combination of Zeeman fields and SOC. Such changes in the
topology signal a quantum phase transition between distinct superfluid phases,
and leave their signatures on some thermodynamic quantities. We also analyze
the possibility of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like nonuniform
superfluid phases with finite center-of-mass momentum and obtain an even richer
phase diagram.Comment: 9 pages with 5 figures; FFLO analysis include
Stability of spin-orbit coupled Fermi gases with population imbalance
We use the self-consistent mean-field theory to analyze the effects of
Rashba-type spin-orbit coupling (SOC) on the ground-state phase diagram of
population-imbalanced Fermi gases throughout the BCS-BEC evolution. We find
that the SOC and population imbalance are counteracting, and that this
competition tends to stabilize the uniform superfluid phase against the phase
separation. However, we also show that the SOC stabilizes (destabilizes) the
uniform superfluid phase against the normal phase for low (high) population
imbalances. In addition, we find topological quantum phase transitions
associated with the appearance of momentum space regions with zero
quasiparticle energies, and study their signatures in the momentum
distribution.Comment: 4+ pages with 3 figures; to appear in PR
Quantum phases of atomic Fermi gases with anisotropic spin-orbit coupling
We consider a general anisotropic spin-orbit coupling (SOC) and analyze the
phase diagrams of both balanced and imbalanced Fermi gases for the entire
BCS--Bose-Einstein condensate (BEC) evolution. In the first part, we use the
self-consistent mean-field theory at zero temperature, and show that the
topological structure of the ground-state phase diagrams is quite robust
against the effects of anisotropy. In the second part, we go beyond the
mean-field description, and investigate the effects of Gaussian fluctuations
near the critical temperature. This allows us to derive the time-dependent
Ginzburg-Landau theory, from which we extract the effective mass of the Cooper
pairs and their critical condensation temperature in the molecular BEC limit.Comment: 10 pages with 7 figures; to appear in PR
Mimicking Nonequilibrium Steady States with Stochastic Pumps
We establish a correspondence between two very general paradigms for systems
that persist away from thermal equilibrium. In the first paradigm, a
nonequilibrium steady state (NESS) is maintained by applying fixed
thermodynamic forces that break detailed balance. In the second paradigm, known
as a stochastic pump (SP), a time-periodic state is maintained by the periodic
variation of a system's external parameters. In both cases, currents are
generated and entropy is produced. Restricting ourselves to discrete-state
systems, we establish a mapping between these scenarios. Given a NESS
characterized by a particular set of stationary probabilities, currents and
entropy production rates, we show how to construct a SP with exactly the same
(time-averaged) values. The mapping works in the opposite direction as well.
These results establish an equivalence between the two paradigms, by showing
that stochastic pumps are able to mimic the behavior of nonequilibrium steady
states, and vice-versa.Comment: 21 pages, 4 figure
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