1,310 research outputs found
Fractional Periodicity of Persistent Currents: A Signature of Broken Internal Symmetry
We show from the symmetries of the many body Hamiltonian, cast into the form
of the Heisenberg (spin) Hamiltonian, that the fractional periodicities of
persistent currents are due to the breakdown of internal symmetry and the spin
Hamiltonian holds the explanation to this transition. Numerical
diagonalizations are performed to show this explicitely. Persistent currents
therefore, provide an easy way to experimentally verify broken internal
symmetry in electronic systems.Comment: minor correction
S-Matrix Formulation of Mesoscopic Systems and Evanescent Modes
The Landauer-Butikker formalism is an important formalism to study mesoscopic
systems. Its validity for linear transport is well established theoretically as
well as experimentally. Akkermans et al [Phys. Rev. Lett. {\bf 66}, 76 (1991)]
had shown that the formalism can be extended to study thermodynamic properties
like persistent currents. It was earlier verified for simple one dimensional
systems. We study this formula very carefully and conclude that it requires
reinterpretation in quasi one dimension. This is essentially because of the
presence of evanescent modes in quasi one dimension.Comment: non
Freeze Out Process with In-Medium Nucleon Mass
We investigate the kinetic freeze out scenario of a nucleon gas through a
finite layer. The in-medium mass modification of nucleons and it's impact on
the freeze out process is studied. A considerable modification of the
thermodynamical parameters temperature, flow-velocity, energy density and
particle density has been found in comparison with evaluations which use a
constant vacuum nucleon mass.Comment: 6 pages, 4 figures, Proceeding of the Conference "Quark Matter 2005",
4th - 9th August 2005, Budapest/Hungar
Long hold times in a two-junction electron trap
The hold time of a single-electron trap is shown to increase
significantly due to suppression of environmentally assisted tunneling events.
Using two rf-tight radiation shields instead of a single one, we demonstrate
increase of by a factor exceeding , up to about 10 hours, for a
trap with only two superconductor (S) -- normal-metal (N) tunnel junctions and
an on-chip resistor (R-SNS structure). In the normal state, the improved
shielding made it possible to observe 100 s, which is in reasonable
agreement with the quantum-leakage-limited level expected for the two-electron
cotunneling process.Comment: 4 pages, 3 figure
Heat Capacity of Mesoscopic Superconducting Disks
We study the heat capacity of isolated giant vortex states, which are good
angular momentum () states, in a mesoscopic superconducting disk using the
Ginzburg-Landau (GL) theory. At small magnetic fields the =0 state
qualitatively behaves like the bulk sample characterized by a discontinuity in
heat capacity at . As the field is increased the discontinuity slowly
turns into a continuous change which is a finite size effect. The higher
states show a continuous change in heat capacity at at all fields. We
also show that for these higher states, the behavior of the peak position
with change in field is related to the paramagnetic Meissner effect
(irreversible) and can lead to an unambiguous observation of positive
magnetization in mesoscopic superconductors.Comment: Final versio
Density Functional Theory of Multicomponent Quantum Dots
Quantum dots with conduction electrons or holes originating from several
bands are considered. We assume the particles are confined in a harmonic
potential and assume the electrons (or holes) belonging to different bands to
be different types of fermions with isotropic effective masses. The density
functional method with the local density approximation is used. The increased
number of internal (Kohn-Sham) states leads to a generalisation of Hund's first
rule at high densities. At low densitites the formation of Wigner molecules is
favored by the increased internal freedom.Comment: 11 pages, 5 figure
Flow of 3He-B through Narrow Channels
The critical current Jc of superfluid 3He-B through 0.8-μm-diam channels has been measured. For small currents the pressure difference ΔP=0 along the flow channels within the resolution, implying small or zero dissipation. ΔP grows rapidly with increasing current above Jc; a clear transition to dissipative flow is thus observed. The temperature dependence of Jc indicates that the superfluid density and the critical temperature are reduced inside the narrow flow channels.Peer reviewe
- …