Enhancement of Local Pairing Correlations in Periodically Driven Mott Insulators

We investigate a model for a Mott insulator in presence of a time-periodic modulated interaction and a coupling to a thermal reservoir. The combination of drive and dissipation leads to non-equilibrium steady states with a large number of doublon excitations, well above the maximum thermal-equilibrium value. We interpret this effect as an enhancement of local pairing correlations, providing analytical arguments based on a Floquet Hamiltonian. Remarkably, this Hamiltonian shows a tendency to develop long-range staggered superconducting correlations. This suggests the possibility of realizing the elusive eta-pairing phase in driven-dissipative Mott Insulators.Comment: 6+5 page

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

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

Transient dynamics of unconventional superconductors: d-wave symmetry and strong correlations

This thesis is about unconventional superconductors out of equilibrium. More precisely, it summarizes our theoretical efforts in addressing a few questions related to the real-time evolution in models displaying unconventional superconductivity. Apart from the purely theoretical interest, the motivation for these studies comes from the recent achievement in the field of ultrafast time-resolved spectroscopy on correlated materials, such as the high-temperature copper-oxide superconductors. The task of describing such systems in nonequilibrium is a very difficult one. In this thesis we attack the problem from two different points of view: \u2022 the anisotropic unconventional d-wave symmetry, \u2022 the strong electron-electron correlations. The thesis is organized as follows: The first part introduces the basic concepts which lay at the foundation of the work presented in the other two parts. In Chapter 1, the concept of unconventional superconductivity is briefly introduced. This mainly includes the high-temperature copper-oxide superconductors and their phenomenology: d-wave symmetry of the super- conducting gap and strong electron-electron interaction. Chapter 2 is devoted to a review of the recent experimental advances in the field of ultrafast spectroscopy of high temperature superconductors and correlated materials, with a particular focus on time- and angle- resolved photoemission spectroscopy. Finally, Chapter 3 is a short review of some works in the field of cold-atom Fermi gases. In the second part we address the physics of the d-wave superconductor after a sudden excitation. First, in Chapter 4 we introduce in some detail a model of mean-field superconductor with a d-wave symmetry. The principal feature of this model is the anisotropy of the gap and the nodal lines along which the gap vanishes. The results concerning the dynamics of the gap after a \u201cquantum quench\u201d are exposed in Chapter 5 where we compare our model to the s-wave superconductor. This comparison allows to identify the consequences of the unconventional symmetry. In Chapter 6 we discuss the spectral features of the transient nonequilibrium state of the d-wave superconductor. This is particularly important to move a first step towards photoemission experiments. In the third part we concentrate on the attractive Hubbard model as a prototype of strongly correlated superconductor. In Chapter 8 we discuss the superconducting state at equilibrium with the use of dynamical mean-field theory. In Chapter 9 we discuss the extension of this technique to systems out of equilibrium. In particular it is described the implementation in the superconducting phase. At the end of the thesis two appendices give some details of the calculations

Aerodynamics of an airfoil with plasma actuators of different kinds and geometries

LAUREA MAGISTRALELo scopo di questo lavoro di tesi, di carattere sperimentale, è lo studio delle prestazioni degli attuatori al plasma, sia di tipo corona che DBD (Dielectric Barrier Discharge), nell'ambito del controllo della separazione su profili aerodinamici ad alti angoli di incidenza. In particolare viene ottimizzata la geometria degli elettrodi a punte triangolari. I parametri geometrici delle punte sono ottimizzati in termini di efficacia nell'aumento di portanza e nella posticipazione dello stallo. Viene inoltre analizzato anche il consumo energetico. Per far ciò sono state effettuate prove di pesate aerodinamiche in galleria del vento su un profilo NACA0015 a quattro diversi numeri di Reynolds (85000, 170000, 255000 e 340000). I risultati ottenuti indicano una superiorità della geometria a punte triangolari rispetto alle configurazioni tradizionali, seppur con un maggior dispendio energetico. Inoltre, è stato presentato un nuovo attuatore corona a tre elettrodi, basato sul principio dell'aumento della densità ionica. Da alcune misure preliminari della velocità indotta è stato possibile stimare come questo attuatore abbia grandi potenzialità future. Infatti, le misure effettuate mostrano velocità e portate superiori sia rispetto agli attuatori tradizionali che agli attuatori a punte.The aim of this thesis work is to study the performances of plasma actuators, both corona and DBD (Dielectric Barrier Discharge) types, as flow control devices on an airfoil at high angles of attack. In particular, serrated-edge electrodes are investigated. A study on a NACA0015 airfoil is performed with the aim of improving its aerodynamic performances, with particular focus on lift coefficient increase and stall delay. The energy consumption of plasma actuators is also evaluated. To do this, lift and drag measurements have been done in a wind tunnel at four different Reynolds numbers (85000, 170000, 255000 and 340000). The results prove that the serrated-edge geometry, when properly designed, overcomes the performances of the straight actuators, although it has a higher energy consumption. Furthermore, a new three-electrodes corona actuator is presented, based on the increase of the ion density. Some preliminary measurements of the induced velocity point out the future potentialities of this actuator. In fact, the new configuration seems to provide higher velocities and higher mass flow rates respect to serrated-edge and traditional geometries

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

Mott memristors based on field-induced carrier avalanche multiplication

We present a theory of Mott memristors whose working principle is the nonlinear carrier avalanche multiplica-tion in Mott insulators subject to strong electric fields. The internal state of the memristor, which determines its resistance, is encoded in the density of doublon and hole excitations in the Mott insulator. In the current-voltage characteristic, insulating and conducting states are separated by a negative-differential-resistance region, leading to hysteretic behavior. Under oscillating voltage, the response of a voltage-controlled, nonpolar memristive system is obtained, with retarded current and pinched hysteresis loop. As a first step towards neuromorphic applications, we demonstrate self-sustained spiking oscillations in a circuit with a parallel capacitor. Being based on electronic excitations only, this memristor is up to several orders of magnitude faster than previous proposals relying on Joule heating or ionic drift

SETBP1 induces transcription of a network of development genes by acting as an epigenetic hub

SETBP1 variants occur as somatic mutations in several hematological malignancies such as atypical chronic myeloid leukemia and as de novo germline mutations in the Schinzel-Giedion syndrome. Here we show that SETBP1 binds to gDNA in AT-rich promoter regions, causing activation of gene expression through recruitment of a HCF1/KMT2A/PHF8 epigenetic complex. Deletion of two AT-hooks abrogates the binding of SETBP1 to gDNA and impairs target gene upregulation. Genes controlled by SETBP1 such as MECOM are significantly upregulated in leukemias containing SETBP1 mutations. Gene ontology analysis of deregulated SETBP1 target genes indicates that they are also key controllers of visceral organ development and brain morphogenesis. In line with these findings, in utero brain electroporation of mutated SETBP1 causes impairment of mouse neurogenesis with a profound delay in neuronal migration. In summary, this work unveils a SETBP1 function that directly affects gene transcription and clarifies the mechanism operating in myeloid malignancies and in the Schinzel- Giedion syndrome caused by SETBP1 mutations.Peer reviewe