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Martin Fliesser

Publications and source records attributed to Martin Fliesser.

5 recordsLinked to original sources
arXiv2001

Conserving and gapless model of the weakly interacting Bose gas

The dielectric formalism is used to set up an approximate description of a spatially homogeneous weakly interacting Bose gas in the collision-less regime, which is both conserving and gap-less, and has coinciding poles of the single-particle Green's function and the density autocorrelation function in the Bose-condensed regime. The approximation takes into account the direct and the exchange interaction in a consistent way. The fulfillment of the generalized Ward identities related to the conservation of particle-number and the breaking of the gauge-symmetry is demonstrated. The dynamics at long wavelengths is considered in detail below and above the phase-transition, numerically and in certain limits also in analytical approximations. The explicit form of the density autocorrelation function and the Green's function is exhibited and discussed.

cond-mat.stat-mech↗
arXiv1998

Classical quasiparticle dynamics and chaos in trapped Bose condensates

In the short wavelength limit the Bogoliubov quasiparticles of trapped Bose-Einstein condensates can be described as classical particles and antiparticles with dynamics in a mixed phase-space. For anisotropic parabolic traps we determine the location of the resonances and study the influence of the sharpness of the condensate surface on the appearance of chaos as the energy of the quasiparticles is lowered from values much larger than to values comparable with the chemical potential.

cond-mat.stat-mech↗
arXiv1997

Classical quasi-particle dynamics in trapped Bose condensates

The dynamics of quasi-particles in repulsive Bose condensates in a harmonic trap is studied in the classical limit. In isotropic traps the classical motion is integrable and separable in spherical coordinates. In anisotropic traps the classical dynamics is found, in general, to be nonintegrable. For quasi-particle energies E much smaller than thechemical potential, besides the conserved quasi-particle energy, we identify two additional nearly conserved phase-space functions. These render the dynamics inside the condensate (collective dynamics) integrable asymptotically for E/chemical potential very small. However, there coexists at the same energy a dynamics confined to the surface of the condensate, which is governed by a classical Hartree-Fock Hamiltonian. We find that also this dynamics becomes integrable for E/chemical potential very small, because of the appearance of an adiabatic invariant. For E/chemical potential of order 1 a large portion of the phase-space supports chaotic motion, both, for the Bogoliubov Hamiltonian and its Hartree-Fock approximant. To exemplify this we exhibit Poincaré surface of sections for harmonic traps with the cylindrical symmetry and anisotropy found in TOP traps. For E/chemical potential very large the dynamics is again governed by the Hartree-Fock Hamiltonian. In the case with cylindrical symmetry it becomes quasi-integrable because the remaining small chaotic components in phase space are tightly confined by tori.

cond-mat↗
arXiv1997

Hydrodynamic excitations of Bose condensates in anisotropic traps

The collective excitations of Bose condensates in anisotropic axially symmetric harmonic traps are investigated in the hydrodynamic and Thomas-Fermi limit. We identify an additional conserved quantity, besides the axial angular momentum and the total energy, and separate the wave equation in elliptic coordinates. The solution is reduced to the algebraic problem of diagonalizing finite dimensional matrices. The classical quasi-particle dynamics in the local density approximation for energies of the order of the chemical potential is shown to be chaotic.

cond-mat↗