38 research outputs found
Instability of Rotationally Tuned Dipolar Bose-Einstein Condensates
The possibility of effectively inverting the sign of the dipole-dipole
interaction, by fast rotation of the dipole polarization, is examined within a
harmonically trapped dipolar Bose-Einstein condensate. Our analysis is based on
the stationary states in the Thomas-Fermi limit, in the corotating frame, as
well as direct numerical simulations in the Thomas-Fermi regime, explicitly
accounting for the rotating polarization. The condensate is found to be
inherently unstable due to the dynamical instability of collective modes. This
ultimately prevents the realization of robust and long-lived rotationally tuned
states. Our findings have major implications for experimentally accessing this
regime.Comment: 9 pages with 5 figure
Coupled pair approach for strongly-interacting trapped fermionic atoms
We present a coupled pair approach for studying few-body physics in
harmonically trapped ultracold gases. The method is applied to a two-component
Fermi system of particles. A stochastically variational gaussian expansion
method is applied, focusing on optimization of the two-body correlations
present in the strongly interacting, or unitary, limit. The groundstate energy
of the four-, six- and eight-body problem with equal spin populations is
calculated with high accuracy and minimal computational effort. We also
calculate the structural properties of these systems and discuss their
implication for the many-body ultracold gas and other few-body calculations.Comment: 7 pages, 4 figure
Universality in rotating strongly interacting gases
We analytically determine the properties of two interacting particles in a
harmonic trap subject to a rotation or a uniform synthetic magnetic field,
where the spherical symmetry of the relative Hamiltonian is preserved.
Thermodynamic quantities such as the entropy and energy are calculated via the
second order quantum cluster expansion. We find that in the strongly
interacting regime the energy is universal, however the entropy changes as a
function of the rotation or synthetic magnetic field strength.Comment: 4 pages, 2 figure
Universality and itinerant ferromagnetism in rotating strongly interacting Fermi gases
We analytically determine the properties of three interacting fermions in a
harmonic trap subject to an external rotation. Thermodynamic quantities such as
the entropy and energy are calculated from the third order quantum virial
expansion. By parameterizing the solutions in the rotating frame we find that
the energy and entropy are universal for all rotations in the strongly
interacting regime. Additionally, we find that rotation suppresses the onset of
itinerant ferromagnetism in strongly interacting repulsive three-body systems.Comment: 5 pages with 3 figure
Anisotropic and long-range vortex interactions in two-dimensional dipolar Bose gases
We perform a theoretical study into how dipole-dipole interactions modify the
properties of superfluid vortices within the context of a two-dimensional
atomic Bose gas of co-oriented dipoles. The reduced density at a vortex acts
like a giant anti-dipole, changing the density profile and generating an
effective dipolar potential centred at the vortex core whose most slowly
decaying terms go as and . These effects modify
the vortex-vortex interaction which, in particular, becomes anisotropic for
dipoles polarized in the plane. Striking modifications to vortex-vortex
dynamics are demonstrated, i.e. anisotropic co-rotation dynamics and the
suppression of vortex annihilation.Comment: PRL accepted, 6 pages, 5 figure
Virial expansion for the optical response of doped two-dimensional semiconductors
We present a quantum virial expansion for the optical response of a doped
two-dimensional semiconductor. As we show, this constitutes a perturbatively
exact theory in the high-temperature or low-doping regime, where the electrons'
thermal wavelength is smaller than their interparticle spacing. The virial
expansion predicts new features of the photoluminescence, such as a non-trivial
shape of the attractive branch related to universal low-energy exciton-electron
scattering and an associated shift of the attractive peak from the trion
energy. Our results are in excellent agreement with recent experiments on doped
monolayer MoSe2 [Zipfel et al., Phys. Rev. B 105, 075311 (2022)] and they imply
that the trion binding energy is likely to have been overestimated in previous
measurements. Our theory furthermore allows us to formally unify two distinct
theoretical pictures that have been applied to this system, with the
conventional trion picture results emerging as a high-temperature and
weak-interaction limit of Fermi polaron theory.Comment: 7 pages, 2 figure
Crossover from exciton polarons to trions in doped two-dimensional semiconductors at finite temperature
We study systematically the role of temperature in the optical response of
doped two-dimensional semiconductors. By making use of a finite-temperature
Fermi-polaron theory, we reveal a crossover from a quantum-degenerate regime
with well-defined polaron quasiparticles to an incoherent regime at high
temperature or low doping where the lowest energy "attractive" polaron
quasiparticle is destroyed, becoming subsumed into a broad trion-hole
continuum. We demonstrate that the crossover is accompanied by significant
qualitative changes in both absorption and photoluminescence. In particular,
with increasing temperature (or decreasing doping), the emission profile of the
attractive branch evolves from a symmetric Lorentzian to an asymmetric peak
with an exponential tail involving trions and recoil electrons at finite
momentum. We discuss the effect of temperature on the coupling to light for
structures embedded into a microcavity, and we show that there can exist
well-defined polariton quasiparticles even when the exciton-polaron
quasiparticle has been destroyed, where the transition from weak to strong
light-matter coupling can be explained in terms of the polaron linewidths and
spectral weights.Comment: 19 pages, 9 figure