333 research outputs found
Scattering of a Dirac electron on a mass barrier
The interaction of a wave packet (and in particular the wave front) with a
mass barrier is investigated in one dimension. We discuss the main features of
the wave packet that are inherent to two-dimensional wave packets, such as
compression during reflection, penetration in the case when the energy is lower
than the height of the barrier, waving tails, precursors, and the retardation
of the reflected and penetrated wave packets. These features depend on the
wave-packet envelope function which we demonstrate by considering the case of a
rectangular wave packet with sharp front and trailing edges and a smooth
Gaussian wave packet. The method of Fourier integral for obtaining the
nonstationary solutions is used.Comment: 12 pages, 9 figure
Scattering of Dirac electrons by circular mass barriers: valley filter and resonant scattering
The scattering of two-dimensional (2D) massless Dirac electrons is
investigated in the presence of a random array of circular mass barriers. The
inverse momentum relaxation time and the Hall factor are calculated and used to
obtain parallel and perpendicular resistivity components within linear
transport theory. We found a non zero perpendicular resistivity component which
has opposite sign for electrons in the different K and K' valleys. This
property can be used for valley filter purposes. The total cross-section for
scattering on penetrable barriers exhibit resonances due to the presence of
quasi-bound states in the barriers that show up as sharp gaps in the
cross-section while for Schr\"{o}dinger electrons they appear as peaks.Comment: 10 pages, 11 figure
Magnetic edge states of impenetrable stripe
The electron motion in a strong perpendicular magnetic field close to the
impenetrable stripe is considered by making use of the singular integral
equation technique. The energy spectrum is calculated and compared with the
energy spectrum of the round antidot.Comment: REVTeX4 format, 9 pages with 9 figures (*.eps
Electronic Band Structure In A Periodic Magnetic Field
We analyze the energy band structure of a two-dimensional electron gas in a
periodic magnetic field of a longitudinal antiferromagnet by considering a
simple exactly solvable model. Two types of states appear: with a finite and
infinitesimal longitudinal mobility. Both types of states are present at a
generic Fermi surface. The system exhibits a transition to an insulating regime
with respect to the longitudinal current, if the electron density is
sufficiently low.Comment: 8 pages, 5 figures; to appear in Phys. Rev. B '9
Resistance effects due to magnetic guiding orbits
The Hall and magnetoresistance of a two dimensional electron gas subjected to
a magnetic field barrier parallel to the current direction is studied as
function of the applied perpendicular magnetic field. The recent experimental
results of Nogaret {\em et al.} [Phys. Rev. Lett. {\bf 84}, 2231 (2000)] for
the magneto- and Hall resistance are explained using a semi-classical theory
based on the Landauer-B\"{u}ttiker formula. The observed positive
magnetoresistance peak is explained as due to a competition between a decrease
of the number of conducting channels as a result of the growing magnetic field,
from the fringe field of the ferromagnetic stripe as it becomes magnetized, and
the disappearance of snake orbits and the subsequent appearance of cycloidlike
orbits.Comment: 7 pages, 7 figure
Electron scattering on circular symmetric magnetic profiles in a two-dimensional electron gas
The quasi-bound and scattered states in a 2DEG subjected to a circular
symmetric steplike magnetic profile with zero average magnetic field are
studied. We calculate the effect of a random distribution of such identical
profiles on the transport properties of a 2DEG. We show that a nonzero Hall
resistance can be obtained, although , and that in some cases it
can even change sign as function of the Fermi energy or the magnetic field
strength. The Hall and magnetoresistance show pronounced resonances apart from
the Landau states of the inner core, corresponding to the so-called quasi-bound
snake orbit states.Comment: 7 pages, 8 figure
Resonant peak splitting for ballistic conductance in magnetic superlattices
We investigate theoretically the resonant splitting of ballistic conductance
peaks in magnetic superlattices. It is found that, for magnetic superlattices
with periodically arranged identical magnetic-barriers, there exists a
general -fold resonant peak splitting rule for ballistic conductance,
which is the analogy of the -fold resonant splitting for transmission in
-barrier electric superlattices (R. Tsu and L. Esaki, Appl. Phys. Lett. {\bf
22}, 562 (1973)).Comment: 9 pages, 3 figures, latex forma
The two electron artificial molecule
Exact results for the classical and quantum system of two vertically coupled
two-dimensional single electron quantum dots are obtained as a function of the
interatomic distance (d) and with perpendicular magnetic field. The classical
system exhibits a second order structural transition as a function of d which
is smeared out and shifted to lower d values in the quantum case. The
spin-singlet - spin-triplet oscillations are shifted to larger magnetic fields
with increasing d and are quenched for a sufficiently large interatomic
distance.Comment: 4 pages, 4 ps figure
Pade approximants for the ground-state energy of closed-shell quantum dots
Analytic approximations to the ground-state energy of closed-shell quantum
dots (number of electrons from 2 to 210) are presented in the form of two-point
Pade approximants. These Pade approximants are constructed from the small- and
large-density limits of the energy. We estimated that the maximum error,
reached for intermediate densities, is less than 3%. Within the present
approximation the ground-state is found to be unpolarized.Comment: 4 pages, RevTeX, 3 ps figure
Magnetic Quantum Dot: A Magnetic Transmission Barrier and Resonator
We study the ballistic edge-channel transport in quantum wires with a
magnetic quantum dot, which is formed by two different magnetic fields B^* and
B_0 inside and outside the dot, respectively. We find that the electron states
located near the dot and the scattering of edge channels by the dot strongly
depend on whether B^* is parallel or antiparallel to B_0. For parallel fields,
two-terminal conductance as a function of channel energy is quantized except
for resonances, while, for antiparallel fields, it is not quantized and all
channels can be completely reflected in some energy ranges. All these features
are attributed to the characteristic magnetic confinements caused by nonuniform
fields.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
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