3,106 research outputs found
Phase of Aharonov-Bohm oscillations in conductance of mesoscopic systems
Motivated by a recent experiment we analyze in detail the phase of
Aharonov-Bohm oscillations across a 1D ring with a stub coupled to one of its
arms, in the presence of a magnetic flux. We demonstrate that there are two
kinds of conductance extremas. One class of them are fixed at particular flux
values and can only change abruptly from a maxima to a minima as incident
energy is varied. We show a different mechanism for such abrupt phase change in
conductance oscillation. We demonstrate that these extremas can exhibit
phase locking". However, the second kind of extremas can shift continuously
as the incident energy is varied.Comment: Figure available on reques
Quantum Waveguide Transport in Serial Stub and Loop Structures
We have studied the quantum transmission properties of serial stub and loop
structures. Throughout we have considered free electron networks and the
scattering arises solely due to the geometric nature of the problem. The band
formation in these geometric structures is analyzed and compared with the
conventional periodic potential scatterers. Some essential differences are
pointed out. We show that a single defect in an otherwise periodic structure
modifies band properties non trivially. By a proper choice of a single defect
one can produce positive energy bound states in continuum in the sense of von
Neumann and Wigner. We also discuss some magnetic properties of loop structures
in the presence of Aharonov-Bohm flux.Comment: Revtex 3.2 version, 27 pages, figures available on request, To appear
in Phys. Rev.
Novel interference effects and a new Quantum phase in mesoscopic systems
Mesoscopic systems have provided an opportunity to study quantum effects
beyond the atomic realm. In these systems quantum coherence prevails over the
entire sample. We discuss several novel effects related to persistent currents
in open systems which do not have analogues in closed systems. Some phenomena
arising simultaneously due to two non-classical effects namely, Aharonov-Bohm
effect and quantum tunneling are presented. Simple analysis of sharp phase
jumps observed in double-slit Aharonov-Bohm experiments is given. Some
consequences of parity violation are elaborated. Finally, we briefly describe
the dephasing of Aharonov-Bohm oscillations in Aharonov-Bohm ring geometry due
to spin-flip scattering in one of the arms. Several experimental manifestations
of these phenomena and their applications are given.Comment: A revie
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
Particle Spectrum of the Supersymmetric Standard Model from the Massless Excitations of a Four Dimensional Superstring
A superstring action is quantised with Neveu Schwarz(NS) and Ramond(R)
boundary conditions. The zero mass states of the NS sector are classified as
the vector gluons, W-mesons, -mesons and scalars containing Higgs. The
fifteen zero mass fermions are obtained from the Ramond sector. A space time
supersymmetric Hamiltonian of the Standard Model is presented without any
conventional SUSY particles
Supersymmetry in the Standard Model
We prove that the bosons and massless fermions of one generation of the
standard model are supersymmetric partners of each other. Except for one
additional auxilliary vector boson, there are no other SUSY particles.Comment: RevTex, 6 pages, uuencoded tar compressed fil
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