988 research outputs found
Non-interacting electrons and the metal-insulator transition in 2D with correlated impurities
While standard scaling arguments show that a system of non-interacting
electrons in two dimensions and in the presence of uncorrelated disorder is
insulating, in this work we discuss the case where inter-impurity correlations
are included. We find that for point-like impurities and an infinite
inter-impurity correlation length a mobility edge exists in 2D even if the
individual impurity potentials are random. In the uncorrelated system we
recover the scaling results, while in the intermediate regime for length scales
comparable to the correlation length, the system behaves like a metal but with
increasing fluctuations, before strong localization eventually takes over for
length scales much larger than the correlation length. In the intermediate
regime, the relevant length scale is not given by the elastic scattering length
but by the inter-impurity correlation length, with important consequences for
high mobility systems.Comment: 4 page
Seeing Anderson Localization
Anderson localization was discovered 50 years ago to describe the propagation
of electrons in the presence of disorder. The main prediction back then, was
the existence of disorder induced localized states, which do not conduct
electricity. Many years later it turns out, that the concept of Anderson
localization is much more general and applies to almost any type of propagation
in time or space, when more than one parameter is relevant (like phase and
amplitude). Here we propose a new optical scheme to literally see Anderson
localization by varying the optical wavelength or angle of incidence to tune
between localized and delocalized states. The occurrence of Anderson
localization in the propagation of light, in particular, has become the focus
of tremendous interest due to the emergence of new optical technologies and
media, such as low dimensional and disordered optical lattices. While several
experiments have reported the measurement of Anderson localization of light,
many of the observations remain controversial because the effects of absorption
and localization have a similar signature, i.e., exponential decrease of the
transmission with the system size. In this work, we discuss a system, where we
can clearly differentiate between absorption and localization effects because
this system is equivalent to a perfect filter, only in the absence of any
absorption. Indeed, only one wavelength is perfectly transmitted and all others
are fully localized. These results were obtained by developing a new
theoretical framework for the average optical transmission through disordered
media.Comment: 5 pages, 4 figure
Comment on ``Periodic wave functions and number of extended states in random dimer systems'
There are no periodic wave-functions in the RDM but close to the critical
energies there exist periodic envelopes. These envelopes are given by the
non-disordered properties of the system.Comment: RevTex file, 1 page, Comment X. Huang, X. Wu and C. Gong, Phys. Rev.
B 55, 11018 (1997
The strengthening of reentrant pinning by collective interactions in the peak effect
Since it was first observed about 40 years ago [1], the peak effect has been
the subject of numerous research mainly impelled by the desire to determine its
exact mechanisms. Despite these efforts, a consensus on this question has yet
to be reached. Experimentally, the peak effect indicates a transition from a
depinned vortex phase to a reentrant pinning phase at high magnetic field. To
study the effects of intrinsic pinning on the peak effect, we consider
FeNiZr superconducting metallic glasses in which the vortex
pinning force varies depending on the Fe content and in which a huge peak
effect is seen as a function of magnetic field. The results are mapped out as a
phase diagram in which it is readily seen that the peak effect becomes broader
with decreasing pinning force. Typically, pinning can be understood by
increased pinning centers, but here, we show that reentrant pinning is due to
the strengthening of interactions (while decreasing pinning strength). Our
results demonstrate the strengthening of the peak effect by collective effects.Comment: 4 pages, 4 figure
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