4 research outputs found
Boson gas in a periodic array of tubes
We report the thermodynamic properties of an ideal boson gas confined in an
infinite periodic array of channels modeled by two, mutually perpendicular,
Kronig-Penney delta-potentials. The particle's motion is hindered in the x-y
directions, allowing tunneling of particles through the walls, while no
confinement along the z direction is considered. It is shown that there exists
a finite Bose- Einstein condensation (BEC) critical temperature Tc that
decreases monotonically from the 3D ideal boson gas (IBG) value as the
strength of confinement is increased while keeping the channel's cross
section, constant. In contrast, Tc is a non-monotonic function of
the cross-section area for fixed . In addition to the BEC cusp, the
specific heat exhibits a set of maxima and minima. The minimum located at the
highest temperature is a clear signal of the confinement effect which occurs
when the boson wavelength is twice the cross-section side size. This
confinement is amplified when the wall strength is increased until a
dimensional crossover from 3D to 1D is produced. Some of these features in the
specific heat obtained from this simple model can be related, qualitatively, to
at least two different experimental situations: He adsorbed within the
interstitial channels of a bundle of carbon nanotubes and
superconductor-multistrand-wires NbSn.Comment: 9 pages, 10 figures, submitte
SO(5) Invariance and Effective Field Theory for High-Tc Superconductors
We set up the effective field theories which describe the SO(5)-invariant
picture of the high-Tc cuprates in various regimes. We use these to get
quantitative conclusions concerning the size of SO(5)-breaking effects. We
consider two applications in detail: (i) the thermodynamic free energy, which
describe the phase diagram and critical behaviour, and (ii) the Lagrangian
governing the interactions of the pseudo-Goldstone bosons with each other and
with the electron quasiparticles deep within the ordered phases. We use these
effective theories to obtain predictions for the critical behaviour near the
possible bicritical point and the pseudo-Goldstone boson dispersion relations,
as well as some preliminary results concerning their contribution to response
functions. We systematically identify which predictions are independent of the
microscopic details of the underlying electron dynamics, and which depend on
more model-dependent assumptions.Comment: 40 pages, plain TeX, companion article for the letter
cond-mat/961107
Bose-Einstein condensation in multilayers
The critical BEC temperature of a non interacting boson gas in a
layered structure like those of cuprate superconductors is shown to have a
minimum , at a characteristic separation between planes . It is
shown that for , increases monotonically back up to the ideal
Bose gas suggesting that a reduction in the separation between planes,
as happens when one increases the pressure in a cuprate, leads to an increase
in the critical temperature. For finite plane separation and penetrability the
specific heat as a function of temperature shows two novel crests connected by
a ridge in addition to the well-known BEC peak at associated with the
3D behavior of the gas. For completely impenetrable planes the model reduces to
many disconnected infinite slabs for which just one hump survives becoming a
peak only when the slab widths are infinite.Comment: Four pages, four figure