35,447 research outputs found
Anderson localization on the Falicov-Kimball model with Coulomb disorder
The role of Coulomb disorder is analysed in the Anderson-Falicov-Kimball
model. Phase diagrams of correlated and disordered electron systems are
calculated within dynamical mean-field theory applied to the Bethe lattice, in
which metal-insulator transitions led by structural and Coulomb disorders and
correlation can be identified. Metallic, Mott insulator, and Anderson insulator
phases, as well as the crossover between them are studied in this perspective.
We show that Coulomb disorder has a relevant role in the phase-transition
behavior as the system is led towards the insulator regime
Three path interference using nuclear magnetic resonance: a test of the consistency of Born's rule
The Born rule is at the foundation of quantum mechanics and transforms our
classical way of understanding probabilities by predicting that interference
occurs between pairs of independent paths of a single object. One consequence
of the Born rule is that three way (or three paths) quantum interference does
not exist. In order to test the consistency of the Born rule, we examine
detection probabilities in three path intereference using an ensemble of
spin-1/2 quantum registers in liquid state nuclear magnetic resonance (LSNMR).
As a measure of the consistency, we evaluate the ratio of three way
interference to two way interference. Our experiment bounded the ratio to the
order of , and hence it is consistent with Born's rule.Comment: 11 pages, 4 figures; Improved presentation of figures 1 and 4,
changes made in section 2 to better describe the experiment, minor changes
throughout, and added several reference
Differential interferometric phases at high spectral resolution as a sensitive physical diagnostic of circumstellar disks
Context. The circumstellar disks ejected by many rapidly rotating B stars
(so-called Be stars) offer the rare opportunity of studying the structure and
dynamics of gaseous disks at high spectral as well as angular resolution. Aims.
This paper explores a newly identified effect in spectro-interferometric phase
that can be used for probing the inner regions of gaseous edge-on disks on a
scale of a few stellar radii. Methods. The origin of this effect (dubbed
central quasi-emission phase signature, CQE-PS) lies in the velocity-dependent
line absorption of photospheric radiation by the circumstellar disk. At high
spectral and marginal interferometric resolution, photocenter displacements
between star and isovelocity regions in the Keplerian disk reveal themselves
through small interferometric phase shifts. To investigate the diagnostic
potential of this effect, a series of models are presented, based on detailed
radiative transfer calculations in a viscous decretion disk. Results. Amplitude
and detailed shape of the CQE-PS depend sensitively on disk density and size
and on the radial distribution of the material with characteristic shapes in
differential phase diagrams. In addition, useful lower limits to the angular
size of the central stars can be derived even when the system is almost
unresolved. Conclusions. The full power of this diagnostic tool can be expected
if it can be applied to observations over a full life-cycle of a disk from
first ejection through final dispersal, over a full cycle of disk oscillations,
or over a full orbital period in a binary system
Spin-polarized current and shot noise in the presence of spin flip in a quantum dot via nonequilibrium Green's functions
Using non-equilibrium Green functions we calculate the spin-polarized current
and shot noise in a ferromagnet--quantum-dot--ferromagnet (FM-QD-FM) system.
Both parallel (P) and antiparallel (AP) magnetic configurations are considered.
Coulomb interaction and coherent spin-flip (similar to a transverse magnetic
field) are taken into account within the dot. We find that the interplay
between Coulomb interaction and spin accumulation in the dot can result in a
bias-dependent current polarization . In particular, can be
suppressed in the P alignment and enhanced in the AP case depending on the bias
voltage. The coherent spin-flip can also result in a switch of the current
polarization from the emitter to the collector lead. Interestingly, for a
particular set of parameters it is possible to have a polarized current in the
collector and an unpolarized current in the emitter lead. We also found a
suppression of the Fano factor to values well below 0.5.Comment: Published version. 13 pages, 7 figure
Anomalous Lattice Response at the Mott Transition in a Quasi-2D Organic Conductor
Discontinuous changes of the lattice parameters at the Mott metal-insulator
transition are detected by high-resolution dilatometry on deuterated crystals
of the layered organic conductor -(BEDT-TTF)Cu[N(CN)]Br.
The uniaxial expansivities uncover a striking and unexpected anisotropy,
notably a zero-effect along the in-plane c-axis along which the electronic
interactions are relatively strong. A huge thermal expansion anomaly is
observed near the end-point of the first-order transition line enabling to
explore the critical behavior with very high sensitivity. The analysis yields
critical fluctuations with an exponent 0.8 0.15
at odds with the novel criticality recently proposed for these materials
[Kagawa \textit{et al.}, Nature \textbf{436}, 534 (2005)]. Our data suggest an
intricate role of the lattice degrees of freedom in the Mott transition for the
present materials.Comment: 4 pages, 4 figure
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