23,527 research outputs found
Little-Parks oscillations near a persistent current loop
We investigate the Little-Parks oscillations caused by a persistent current
loop set on the top edge of a mesoscopic superconducting thin-walled cylinder
with a finite height. For a short cylinder the Little-Parks oscillations are
approximately the same ones as the standard effect, as there is only one
magnetic flux piercing the cylinder. For a tall cylinder the inhomogeneity of
the magnetic field makes different magnetic fluxes pierce the cylinder at
distinct heights and we show here that this produces two distinct Little-Parks
oscillatory regimes according to the persistent current loop. We show that
these two regimes, and also the transition between them, are observable in
current measurements done in the superconducting cylinder. The two regimes stem
from different behavior along the height, as seen in the order parameter,
numerically obtained from the Ginzburg-Landau theory through the finite element
methodComment: 13 pages, 12 figure
Magnetocaloric effect in integrable spin-s chains
We study the magnetocaloric effect for the integrable antiferromagnetic
high-spin chain. We present an exact computation of the Gr\"uneisen parameter,
which is closely related to the magnetocaloric effect, for the quantum spin-s
chain on the thermodynamical limit by means of Bethe ansatz techniques and the
quantum transfer matrix approach. We have also calculated the entropy S and the
isentropes in the (H,T) plane. We have been able to identify the quantum
critical points H_c^{(s)}=2/(s+1/2) looking at the isentropes and/or the
characteristic behaviour of the Gr\"uneisen parameter.Comment: 6 pages, 3 figure
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