37 research outputs found
Intrinsic instability of electronic interfaces with strong Rashba coupling
We consider a model for the two-dimensional electron gas formed at the
interface of oxide heterostructures, which includes a Rashba spin-orbit
coupling proportional to the electric field perpendicular to the interface.
Based on the standard mechanism of polarity catastrophe, we assume that the
electric field is proportional to the electron density. Under these simple and
general assumptions, we show that a phase separation instability occurs for
realistic values of the spin-orbit coupling and of the band parameters. This
could provide an intrinsic mechanism for the recently observed inhomogeneous
phases at the LaAlO_3/SrTiO_3 or LaTiO_3/SrTiO_3 interfaces.Comment: 5 pages, 4 figure
Floquet prethermalization and Rabi oscillations in optically excited Hubbard clusters
We study the properties of Floquet prethermal states in two-dimensional Mott-insulating Hubbard clusters under continuous optical excitation. With exact-diagonalization simulations, we show that Floquet prethermal states emerge not only off resonance, but also for resonant excitation, provided a small field amplitude. In the resonant case, the long-lived quasi-stationary Floquet states are characterized by Rabi oscillations of observables such as double occupation and kinetic energy. At stronger fields, thermalization to infinite temperature is observed. We provide explanations to these results by means of time-dependent perturbation theory. The main findings are substantiated by a finite-size analysis
Phase diagrams of voltage-gated oxide interfaces with strong Rashba coupling
We propose a model for the two-dimensional electron gas formed at the
interface of oxide heterostructures that includes a Rashba spin-orbit coupling
proportional to an electric field oriented perpendicularly to the interface.
Taking into account the electron density dependence of this electric field
confining the electron gas at the interface, we report the occurrence of a
phase separation instability (signaled by a negative compressibility) for
realistic values of the spin-orbit coupling and of the electronic
band-structure parameters at zero temperature. We extend the analysis to finite
temperatures and in the presence of an in-plane magnetic field, thereby
obtaining two phase diagrams which exhibit a phase separation dome. By varying
the gating potential the phase separation dome may shrink and vanish at zero
temperature into a quantum critical point where the charge fluctuates
dynamically. Similarly the phase separation may be spoiled by a planar magnetic
field even at zero temperature leading to a line of quantum critical points.Comment: 17 pages, 17 figure
Multilayer perceptron neural networks model for meteosat second generation SEVIRI daytime cloud masking
A multilayer perceptron neural network cloud mask for Meteosat Second Generation SEVIRI (Spinning Enhanced Visible and Infrared Imager) images is introduced and evaluated. The model is trained for cloud detection on MSG SEVIRI daytime data. It consists of a multi-layer perceptron with one hidden sigmoid layer, trained with the error back-propagation algorithm. The model is fed by six bands of MSG data (0.6, 0.8, 1.6, 3.9, 6.2 and 10.8 μm) with 10 hidden nodes. The multiple-layer perceptrons lead to a cloud detection accuracy of 88.96%, when trained to map two predefined values that classify cloud and clear sky. The network was further evaluated using sixty MSG images taken at different dates. The network detected not only bright thick clouds but also thin or less bright clouds. The analysis demonstrated the feasibility of using machine learning models of cloud detection in MSG SEVIRI imagery
SULLA SUPERFICIE DI DISCONTINUITÀ' ALLA PROFONDITÀ' DI 950 K M CIRCA
Si portano nuovi elementi in favore dell'esistenza di una superficiedi discontinuità nel mantello terrestre, capace di riflettere unapiccola percentuale dell'energia sismica incidente. Detta superficiedovrebbe trovarsi ad una profondità di 950 km circa