570 research outputs found
Effects of spin-orbit coupling on the Berezinskii-Kosterlitz-Thouless transition and the vortex-antivortex structure in two-dimensional Fermi gases
We investigate the Berezinskii-Kosterlitz-Thouless (BKT) transition in a
two-dimensional (2D) Fermi gas with spin-orbit coupling (SOC), as a function of
the two-body binding energy and a perpendicular Zeeman field. By including a
generic form of the SOC, as a function of Rashba and Dresselhaus terms, we
study the evolution between the experimentally relevant equal
Rashba-Dresselhaus (ERD) case and the Rashba-only (RO) case. We show that in
the ERD case, at fixed non-zero Zeeman field, the BKT transition temperature
is increased by the effect of SOC for all values of the binding
energy. We also find a significant increase in the value of the Clogston limit
compared to the case without SOC. Furthermore, we demonstrate that the
superfluid density tensor becomes anisotropic (except in the RO case), leading
to an anisotropic phase-fluctuation action that describes elliptic vortices and
antivortices, which become circular in the RO limit. This deformation
constitutes an important experimental signature for superfluidity in a 2D Fermi
gas with ERD SOC. Finally, we show that the anisotropic sound velocities
exhibit anomalies at low temperatures, in the vicinity of quantum phase
transitions between topologically distinct uniform superfluid phases.Comment: 5 pages, 3 figure
Quantum phase transitions and Berezinskii-Kosterlitz-Thouless temperature in a two-dimensional spin-orbit-coupled Fermi gas
We study the effect of spin-orbit coupling on both the zero-temperature and
non-zero temperature behavior of a two-dimensional (2D) Fermi gas. We include a
generic combination of Rashba and Dresselhaus terms into the system
Hamiltonian, which allows us to study both the experimentally relevant
equal-Rashba-Dresselhaus (ERD) limit and the Rashba-only (RO) limit. At zero
temperature, we derive the phase diagram as a function of the two-body binding
energy and Zeeman field. In the ERD case, this phase diagram reveals several
topologically distinct uniform superfluid phases, classified according to the
nodal structure of the quasiparticle excitation energies. Furthermore, we use a
momentum dependent SU(2)-rotation to transform the system into a generalized
helicity basis, revealing that spin-orbit coupling induces a triplet pairing
component of the order parameter. At non-zero temperature, we study the
Berezinskii-Kosterlitz-Thouless (BKT) phase transition by including phase
fluctuations of the order parameter up to second order. We show that the
superfluid density becomes anisotropic due to the presence of spin-orbit
coupling (except in the RO case). This leads both to elliptic vortices and
antivortices, and to anisotropic sound velocities. The latter prove to be
sensitive to quantum phase transitions between topologically distinct phases.
We show further that at a fixed non-zero Zeeman field, the BKT critical
temperature is increased by the presence of ERD spin-orbit coupling.
Subsequently, we demonstrate that the Clogston limit becomes infinite:
remains non-zero at all finite values of the Zeeman field. We
conclude by extending the quantum phase transition lines to non-zero
temperature, using the nodal structure of the quasiparticle spectrum, thus
connecting the BKT critical temperature with the zero-temperature results.Comment: 17 pages, 7 figure
Perspective on Quantum Bubbles in Microgravity
Progress in understanding quantum systems has been driven by the exploration
of the geometry, topology, and dimensionality of ultracold atomic systems. The
NASA Cold Atom Laboratory (CAL) aboard the International Space Station has
enabled the study of ultracold atomic bubbles, a terrestrially-inaccessible
topology. Proof-of-principle bubble experiments have been performed on CAL with
an rf-dressing technique; an alternate technique (dual-species
interaction-driven bubbles) has also been proposed. Both techniques can drive
discovery in the next decade of fundamental physics research in microgravity.Comment: 17 pages, 2 figure
- …