65 research outputs found
Spin wave theory for 2D disordered hard-core bosons
A spin-wave (SW) approach for hard-core bosons is presented to treat the
problem of two dimensional boson localization in a random potential. After a
short review of the method to compute 1/S-corrected observables, the case of
random on-site energy is discussed. Whereas the mean-field solution does not
display a Bose glass (BG) phase, 1/S corrections do capture BG physics. In
particular, the localization of SW excitations is discussed through the inverse
participation ratio.Comment: TIDS15 conferenc
Classical diffusive dynamics for the quasiperiodic kicked rotor
We study the classical dynamics of a quasiperiodic kicked rotor, whose
quantum counterpart is known to be an equivalent of the 3D Anderson model.
Using this correspondence allowed for a recent experimental observation of the
Anderson transition with atomic matter waves. In such a context, it is
particularly important to assert the chaotic character of the classical
dynamics of this system. We show here that it is a 3D anisotropic diffusion.
Our simple analytical predictions for the associated diffusion tensor are found
in good agreement with the results of numerical simulations.Comment: 8 pages, 7 figures, submitted to Jour. Mod. Opt
Scanning Gate Microscopy of Quantum Contacts Under Parallel Magnetic Field: Beating Patterns Between Spin-Split Transmission Peaks or Channel Openings
We study the conductance of an electron interferometer created in a two
dimensional electron gas between a nanostructured contact and the depletion
region induced by the charged tip of a scanning gate microscope. Using
non-interacting models, we study the beating pattern of interference fringes
exhibited by the images giving as a function of the tip position when a
parallel magnetic field is applied. The analytical solution of a simplified
model allows us to distinguish between two cases: (i) If the field is applied
everywhere, the beating of Fabry-P\'erot oscillations of opposite spins gives
rise to interference rings which can be observed at low temperatures when the
contact is open between spin-split transmission resonances. (ii) If the field
acts only upon the contact, the interference rings cannot be observed at low
temperatures, but only at temperatures of the order of the Zeeman energy. For a
contact made of two sites in series, a model often used for describing an
inversion-symmetric double-dot setup, a pseudo-spin degeneracy is broken by the
inter-dot coupling and a similar beating effect can be observed without
magnetic field at temperatures of the order of the interdot coupling.
Eventually, numerical studies of a quantum point contact with quantized
conductance plateaus confirm that a parallel magnetic field applied everywhere
or only upon the contact gives rises to similar beating effects between
spin-split channel openings.Comment: 11 pages, 17 figure
Coherent back and forward scattering peaks in the quantum kicked rotor
We propose and analyze an experimental scheme using the quantum kicked rotor
to observe the newly-predicted coherent forward scattering peak together with
its long-known twin brother, the coherent backscattering peak. Contrary to
coherent backscattering, which arises already under weak-localization
conditions, coherent forward scattering is only triggered by Anderson or strong
localization. So far, coherent forward scattering has not been observed in
conservative systems with elastic scattering by spatial disorder. We propose to
turn to the quantum kicked rotor, which has a long and succesful history as an
accurate experimental platform to observe dynamical localization, i.e.,
Anderson localization in momentum space. We analyze the coherent forward
scattering effect for the quantum kicked rotor by extensive numerical
simulations, both in the orthogonal and unitary class of disordered quantum
systems, and show that an experimental realization involving phase-space
rotation techniques is within reach of state-of-the-art cold-atom experiments.Comment: 26 pages, 11 figure
Thermal Enhancement of Interference Effects in Quantum Point Contacts
We study an electron interferometer formed with a quantum point contact and a
scanning probe tip in a two-dimensional electron gas. The images giving the
conductance as a function of the tip position exhibit fringes spaced by half
the Fermi wavelength. For a contact opened at the edges of a quantized
conductance plateau, the fringes are enhanced as the temperature T increases
and can persist beyond the thermal length l_T. This unusual effect is explained
assuming a simplified model: The fringes are mainly given by a contribution
which vanishes when T -> 0 and has a decay characterized by a T-independent
scale
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