Signatures of Dissipation Driven Quantum Phase Transition in Rabi Model.

By using the worldline Monte Carlo technique, matrix product state, and a variational approach à la Feynman, we investigate the equilibrium properties and relaxation features of the dissipative quantum Rabi model, where a two level system is coupled to a linear harmonic oscillator embedded in a viscous fluid. We show that, in the Ohmic regime, a Beretzinski-Kosterlitz-Thouless quantum phase transition occurs by varying the coupling strength between the two level system and the oscillator. This is a nonperturbative result, occurring even for extremely low dissipation magnitude. By using state-of-the-art theoretical methods, we unveil the features of the relaxation towards the thermodynamic equilibrium, pointing out the signatures of quantum phase transition both in the time and frequency domains. We prove that, for low and moderate values of the dissipation, the quantum phase transition occurs in the deep strong coupling regime. We propose to realize this model by coupling a flux qubit and a damped LC oscillator.

Thermoelectric efficiency of molecular junctions.

Focus of the review is on experimental set-ups and theoretical proposals aimed to enhance thermoelectric performances of molecular junctions. In addition to charge conductance, the thermoelectric parameter commonly measured in these systems is the thermopower, which is typically rather low. We review recent experimental outcomes relative to several junction configurations used to optimize the thermopower. On the other hand, theoretical calculations provide estimations of all the thermoelectric parameters in the linear and non-linear regime, in particular of the thermoelectric figure of merit and efficiency, completing our knowledge of molecular thermoelectricity. For this reason, the review will mainly focus on theoretical studies analyzing the role of not only electronic, but also of the vibrational degrees of freedom. Theoretical results about thermoelectric phenomena in the coherent regime are reviewed focusing on interference effects which play a significant role in enhancing the figure of merit. Moreover, we review theoretical studies including the effects of molecular many-body interactions, such as electron-vibration couplings, which typically tend to reduce the efficiency. Since a fine tuning of many parameters and coupling strengths is required to optimize the thermoelectric conversion in molecular junctions, new theoretically proposed set-ups are discussed in the conclusions.

Electronic properties and Schottky barriers at ZnO-metal interfaces from first principles.

First principles calculations were performed to study the interface electronic structure and the Schottky barrier heights (SBHs) of ZnO-metal interfaces. Different kinds of metals were considered with different chemistries on the polar (0 0 0 1) and (0 0 0 1¯) ZnO surfaces. The projection of the density of states on the atomic orbitals of the interface atoms reveals that two kinds of interface electronic states appear: states due to the chemical bonding which appear at well defined energies and conventional metal-induced gap states associated with a smooth density of states in the bulk ZnO band gap region. The relative weight and distribution of the two classes of states depend on both the ZnO substrate termination and on the metal species. SBHs are found to be very sensitive to the specific interface chemical bonding. In particular, it is possible to note the occurrence of either Schottky barriers or Ohmic contacts. Our results have been compared with experiments and with available phenomenological theories, which estimate the SBH from few characteristic material parameters. Finally, the electronic and structural contributions to the SBH have been singled out and related to the different charge transfers occurring at the different interfaces.

Ubiquitous long-range antiferromagnetic coupling across the interface between superconducting and ferromagnetic oxides.

The so-called proximity effect is the manifestation, across an interface, of the systematic competition between magnetic order and superconductivity. This phenomenon has been well documented and understood for conventional superconductors coupled with metallic ferromagnets; however it is still less known for oxide materials, where much higher critical temperatures are offered by copper oxide-based superconductors. Here we show that, even in the absence of direct Cu-O-Mn covalent bonding, the interfacial CuO2 planes of superconducting La(1.85)Sr(0.15)CuO(4) thin films develop weak ferromagnetism associated to the charge transfer of spin-polarised electrons from the La(0.66)Sr(0.33)MnO(3) ferromagnet. Theoretical modelling confirms that this effect is general to all cuprate/manganite heterostructures and the presence of direct bonding only affects the strength of the coupling. The Dzyaloshinskii-Moriya interaction, also at the origin of the weak ferromagnetism of bulk cuprates, propagates the magnetisation from the interface CuO2 planes into the superconductor, eventually depressing its critical temperature.

Noise-assisted charge pump in elastically deformable molecular junctions.

We study a charge pump realized with an elastically deformable quantum dot whose center of mass follows a nonlinear stochastic dynamics. The interplay of noise, nonlinear effects, dissipation and interaction with an external time-dependent driving on the pumped charge is fully analyzed. The results show that the quantum pumping mechanism not only is not destroyed by the force fluctuations, but it becomes stronger when the forcing signal frequency is tuned close to the resonance of the vibrational mode. The robustness of the quantum pump with temperature is also investigated and an exponential decay of the pumped charge is found when the coupling to the vibrational mode is present. Implications of our results for nanoelectromechanical systems are also discussed.

Low-temperature magnetic and transport anisotropy in manganite thin films.

The stability of striped magnetic phases in films of La(1-x)A(x)MnO(3) perovskites is investigated. A variational analysis is developed for different film thicknesses at fixed hole density (x = 0.3) and the competition among magnetic phases as a function of the transfer integral and the temperature is analyzed. The stabilization of an in-plane striped magnetic phase is observed with reducing the film thickness at low temperatures below the metal-insulator transition temperature. Within the adopted variational scheme, treating perturbatively the residual electron-phonon interaction, the dependence of the in-plane resistivity on temperature for different thicknesses is calculated. At low temperatures, due to the striped magnetic phase, the resistivity shows an important in-plane anisotropy. The obtained results are found to be consistent with experiments.

[Avatars in face transplants]. / Les avatars de la transplantation à la face.

Avatar carries a pejorative connotation often related to an unfortunate hazard. In face transplants, incarnations were numerous. The analysis of their evolution through time and increasing sophistication of procedures turn out to be informative regarding the wide disrepairs in the craniofacial area. The authors report the principal constraints of face transplant and the evolution in minds to deal with it.

Rashba quantum wire: exact solution and ballistic transport.

The effect of Rashba spin-orbit interaction in quantum wires with hard-wall boundaries is discussed. The exact wavefunction and eigenvalue equation are worked out, pointing out the mixing between the spin and spatial parts. The spectral properties are also studied within perturbation theory with respect to the strength of the spin-orbit interaction and diagonalization procedure. A comparison is made with the results of a simple model, the two-band model, that takes account only of the first two sub-bands of the wire. Finally, the transport properties within the ballistic regime are analytically calculated for the two-band model and through a tight-binding Green function for the entire system. Single and double interfaces separating regions with different strengths of spin-orbit interaction are analysed by injecting carriers into the first and the second sub-band. It is shown that in the case of a single interface the spin polarization in the Rashba region is different from zero, and in the case of two interfaces the spin polarization shows oscillations due to spin-selective bound states.

Validity of the Franck-Condon principle in the optical spectroscopy: optical conductivity of the Fröhlich polaron.

The optical absorption of the Fröhlich polaron model is obtained by an approximation-free diagrammatic Monte Carlo method and compared with two new approximate approaches that treat lattice relaxation effects in different ways. We show that: (i) a strong coupling expansion, based on the Franck-Condon principle, well describes the optical conductivity for large coupling strengths (alpha > 10); (ii) a memory function formalism with phonon broadened levels reproduces the optical response for weak coupling strengths (alpha < 6) taking the dynamic lattice relaxation into account. In the coupling regime 6 < alpha < 10, the optical conductivity is a rapidly changing superposition of both Franck-Condon and dynamic contributions.

[Folliculitis and abscessed nodular perifolliculitis of the upper limb caused by Trichophyton mentagrophytes, presumably corticoid-related]. / Foliculitis y perifoliculitis nodular abscedada de miembro superior por Trichophyton mentagrophytes, presumiblemente cortisónica.

The authors present a follicolitis and perifolliculitis case with abscess and profound nodules, unfolded on a patient who had been subjected to an abusive local an general treatment with corticoids. That process had progressed with similar characteristics to Majocchi's tricophytic granuloma, although this case appeared over the application of that therapeutic. The allergological study could prove a depression of the cellular immunity, but at the same time it demonstrated an abnormal reaction, as an anaphylactoid one, at trychophytin and penicillin.

[Variable pseudoerythroplasic telangiectasis balanitis]. / Balanitis pseudoeritroplástica telangiectásica variable

This is a special case of balanitis, that authors separate from entities clinically established such as Erthroplasie of Queyrat, Balanitis of Zoon, Liquenoide Balantis with Plasmocytes and the Balantis of Sulsberger and Garbe's illness. The V. P. T. B. is clinically characterized by the presence of telangiectasies, ertroplasiform aspect, without any infiltration, non purpure, the V. P. T. B. goes through a first period truly esythematous and a second one in which these is also desquamation. That cycle is completed in a month. At the histopathologic level, the most important characteristics are: epidermis with its Malpighian layer in a normal state, the basal layers showing hidropic degeneration. The repper dermis shows a lichenoid picture that, in certain places affects the basal layer. The infiltrate is composed of: lymphocytes, monocytes and plasmocytes. Numerous telangiectasies are also observed.