6,090 research outputs found
Surface-enhanced pair transfer in quadrupole states of neutron-rich Sn isotopes
We investigate the neutron pair transfer modes associated with the low-lying
quadrupole states in neutron-rich Sn isotopes by means of the quasiparticle
random phase approximation based on the Skyrme-Hartree-Fock-Bogoliubov mean
field model. The transition strength of the quadrupole pair-addition mode
feeding the state is enhanced in the Sn isotopes with . The
transition density of the pair-addition mode has a large spatial extension in
the exterior of nucleus, reaching far to fm. The quadrupole
pair-addition mode reflects sensitively a possible increase of the effective
pairing interaction strength in the surface and exterior regions of
neutron-rich nuclei.Comment: 14 page
On Koopman-von Neumann Waves II
In this paper we continue the study, started in [1], of the operatorial
formulation of classical mechanics given by Koopman and von Neumann (KvN) in
the Thirties. In particular we show that the introduction of the KvN Hilbert
space of complex and square integrable "wave functions" requires an enlargement
of the set of the observables of ordinary classical mechanics. The possible
role and the meaning of these extra observables is briefly indicated in this
work. We also analyze the similarities and differences between non selective
measurements and two-slit experiments in classical and quantum mechanics.Comment: 18+1 pages, 1 figure, misprints fixe
Toward an AdS/cold atoms correspondence: a geometric realization of the Schroedinger symmetry
We discuss a realization of the nonrelativistic conformal group (the
Schroedinger group) as the symmetry of a spacetime. We write down a toy model
in which this geometry is a solution to field equations. We discuss various
issues related to nonrelativistic holography. In particular, we argue that free
fermions and fermions at unitarity correspond to the same bulk theory with
different choices for the near-boundary asymptotics corresponding to the source
and the expectation value of one operator. We describe an extended version of
nonrelativistic general coordinate invariance which is realized
holographically.Comment: 14 pages; v2: typos fixed, published versio
Rotationally-invariant slave-bosons for Strongly Correlated Superconductors
We extend the rotationally invariant formulation of the slave-boson method to
superconducting states. This generalization, building on the recent work by
Lechermann et al. [Phys. Rev. B {\bf 76}, 155102 (2007)], allows to study
superconductivity in strongly correlated systems. We apply the formalism to a
specific case of strongly correlated superconductivity, as that found in a
multi-orbital Hubbard model for alkali-doped fullerides, where the
superconducting pairing has phonic origin, yet it has been shown to be favored
by strong correlation owing to the symmetry of the interaction. The method
allows to treat on the same footing the strong correlation effects and the
interorbital interactions driving superconductivity, and to capture the physics
of strongly correlated superconductivity, in which the proximity to a Mott
transition favors the superconducting phenomenon.Comment: 18 pages, 7 figure
Reply to "Comment on 'Topological stability of the half-vortices in spinor exciton-polariton condensates'"
In a recent work [H. Flayac, I.A. Shelykh, D.D. Solnyshkov and G. Malpuech,
Phys. Rev. B 81, 045318 (2010)], we have analyzed the effect of the TE-TM
splitting on the stability of the exciton-polariton vortex states. We
considered classical vortex solutions having cylindrical symmetry and we found
that the so-called half-vortex states [Yu. G. Rubo, Phys. Rev. Lett. 99, 106401
(2007)] are not solutions of the stationary Gross-Pitaevskii equation. In their
Comment [M. Toledo Solano, Yu.G. Rubo, Phys. Rev. B 82, 127301 (2010)], M.
Toledo Solano and Yuri G. Rubo claim that this conclusion is misleading and
pretend to demonstrate the existence of static half-vortices in an
exciton-polariton condensate in the presence of TE-TM splitting. In this reply
we explain why this assertion is not demonstrated satisfactorily.Comment: 3 Pages, no figur
BCS - BEC crossover at T=0: A Dynamical Mean Field Theory Approach
We study the T=0 crossover from the BCS superconductivity to Bose-Einstein
condensation in the attractive Hubbard Model within dynamical mean field
theory(DMFT) in order to examine the validity of Hartree-Fock-Bogoliubov (HFB)
mean field theory, usually used to describe this crossover, and to explore
physics beyond it. Quantum fluctuations are incorporated using iterated
perturbation theory as the DMFT impurity solver. We find that these
fluctuations lead to large quantitative effects in the intermediate coupling
regime leading to a reduction of both the superconducting order parameter and
the energy gap relative to the HFB results. A qualitative change is found in
the single-electron spectral function, which now shows incoherent spectral
weight for energies larger than three times the gap, in addition to the usual
Bogoliubov quasiparticle peaks.Comment: 11 pages,12 figures, Published versio
Electron-hole pair condensation at the semimetal-semiconductor transition: a BCS-BEC crossover scenario
We act on the suggestion that an excitonic insulator state might
separate---at very low temperatures---a semimetal from a semiconductor and ask
for the nature of these transitions. Based on the analysis of electron-hole
pairing in the extended Falicov-Kimball model, we show that tuning the Coulomb
attraction between both species, a continuous crossover between a BCS-like
transition of Cooper-type pairs and a Bose-Einstein condensation of preformed
tightly-bound excitons might be achieved in a solid-state system. The precursor
of this crossover in the normal state might cause the transport anomalies
observed in several strongly correlated mixed-valence compounds.Comment: 5 pages, 5 figures, substantially revised versio
Vortex structures and zero energy states in the BCS-to-BEC evolution of p-wave resonant Fermi gases
Multiply quantized vortices in the BCS-to-BEC evolution of p-wave resonant
Fermi gases are investigated theoretically. The vortex structure and the
low-energy quasiparticle states are discussed, based on the self-consistent
calculations of the Bogoliubov-de Gennes and gap equations. We reveal the
direct relation between the macroscopic structure of vortices, such as particle
densities, and the low-lying quasiparticle state. In addition, the net angular
momentum for multiply quantized vortices with a vorticity is found to
be expressed by a simple equation, which reflects the chirality of the Cooper
pairing. Hence, the observation of the particle density depletion and the
measurement of the angular momentum will provide the information on the
core-bound state and -wave superfluidity. Moreover, the details on the zero
energy Majorana state are discussed in the vicinity of the BCS-to-BEC
evolution. It is demonstrated numerically that the zero energy Majorana state
appears in the weak coupling BCS limit only when the vortex winding number is
odd. There exist the branches of the core bound states for a vortex
state with vorticity , whereas only one of them can be the zero energy.
This zero energy state vanishes at the BCS-BEC topological phase transition,
because of interference between the core-bound and edge-bound states.Comment: 15 pages, 9 figures, published versio
p-Wave superfluid and phase separation in atomic Bose-Fermi mixture
We consider a system of repulsively interacting Bose-Fermi mixtures of spin
polarized uniform atomic gases at zero temperature. We examine possible
realization of p-wave superfluidity of fermions due to an effective attractive
interaction via density fluctuations of Bose-Einstein condensate within
mean-field approximation. We find the ground state of the system by direct
energy comparison of p-wave superfluid and phase-separated states, and suggest
an occurrence of the p-wave superfluid for a strong boson-fermion interaction
regime. We study some signatures in the p-wave superfluid phase, such as
anisotropic energy gap and quasi-particle energy in the axial state, that have
not been observed in spin unpolarized superfluid of atomic fermions. We also
show that a Cooper pair is a tightly bound state like a diatomic molecule in
the strong boson-fermion coupling regime and suggest an observable indication
of the p-wave superfluid in the real experiment.Comment: 7 pages, 6 figur
Density-matrix functionals for pairing in mesoscopic superconductors
A functional theory based on single-particle occupation numbers is developed
for pairing. This functional, that generalizes the BCS approach, directly
incorporates corrections due to particle number conservation. The functional is
benchmarked with the pairing Hamiltonian and reproduces perfectly the energy
for any particle number and coupling.Comment: 4 pages, 4 figures, revised versio
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