6,188 research outputs found
Properties of nano-graphite ribbons with zigzag edges -- Difference between odd and even legs --
Persistent currents and transport properties are investigated for the
nano-graphite ribbons with zigzag shaped edges with paying attention to system
length dependence. It is found that both the persistent current in the
isolated ring and the conductance of the system connected to the perfect leads
show the remarkable dependences. In addition, the dependences for the
systems with odd legs and those with even legs are different from each other.
On the persistent current, the amplitude for the cases with odd legs shows
power-low behavior as with being the number of legs, whereas the
maximum of it decreases exponentially for the cases with even legs. The
conductance per one spin normalized by behaves as follows. In the even
legs cases, it decays as , whereas it reaches to unity for in the odd legs cases. Thus, the material is shown to have a remarkable
property that there is the qualitative difference between the systems with odd
legs and those with even legs even in the absence of the electron-electron
interaction.Comment: 4 pagaes, 8 figures, LT25 conference proceeding, accepted for
publication in Journal of Physics: Conference Serie
Comment on ``Effective Mass and g-Factor of Four Flux Quanta Composite Fermions"
In a recent Letter, Yeh et al.[Phys. Rev. Lett. 82, 592 (1999)] have shown
beautiful experimental results which indicate that the composite fermions with
four flux quanta (CF) behave as fermions with mass and spin just like those
with two flux quanta. They observed the collapse of the fractional quantum Hall
gaps when the following condition is satisfied with some integer ,
, where and
are the g-factor and the cyclotron frequency of the CF,
respectively. However, in their picture the gap at the Fermi energy remains
always finite even if the above condition is satisfied, thus the reason of the
collapse was left as a mystery. In this comment it is shown that part of the
mystery is resolved by considering the electron-hole symmetry properly.Comment: 2 pages, RevTeX. Minor chang
On transport in quantum Hall systems with constrictions
Motivated by recent experimental findings, we study transport in a simple
phenomenological model of a quantum Hall edge system with a gate-voltage
controlled constriction lowering the local filling factor. The current
backscattered from the constriction is seen to arise from the matching of the
properties of the edge-current excitations in the constriction () and
bulk () regions. We develop a hydrodynamic theory for bosonic edge
modes inspired by this model, finding that a competition between two tunneling
process, related by a quasiparticle-quasihole symmetry, determines the fate of
the low-bias transmission conductance. In this way, we find satisfactory
explanations for many recent puzzling experimental results.Comment: 4 pages, 4 figure
Density Matrix Renormalization Group and the Nuclear Shell Model
We describe the use of the Density Matrix Renormalization Group method as a
means of approximately solving large-scale nuclear shell-model problems. We
focus on an angular-momentum-conserving variant of the method and report test
results for the nucleus . The calculation is able to reproduce both
the ground state energy and the energy of the first excited state, by
diagonalizing matrices much smaller than those of the full shell model.Comment: 7 pages, 3 figures; To appears in Phys. Rev.
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