Interactions and superconductivity in heavily doped MoS2

We analyze the microscopic origin and the physical properties of the superconducting phase recently observed in MoS$_2$. We show how the combination of the valley structure of the conduction band, the density dependence of the screening of the long range Coulomb interactions, the short range electronic repulsion, and the relative weakness of the electron-phonon interactions, makes possible the existence of a phase where the superconducting order parameter has opposite signs in different valleys, resembling the superconductivity found in the pnictides and cuprates

Assessment of thermal instabilities and oscillations in multifinger heterojunction bipolar transistors through a harmonic-balance-based CAD-oriented dynamic stability analysis technique

We present a novel analysis of thermal instabilities and oscillations in multifinger heterojunction bipolar transistors (HBTs), based on a harmonic-balance computer-aided-design (CAD)-oriented approach to the dynamic stability assessment. The stability analysis is carried out in time-periodic dynamic conditions by calculating the Floquet multipliers of the limit cycle representing the HBT working point. Such a computation is performed directly in the frequency domain, on the basis of the Jacobian of the harmonic-balance problem yielding the limit cycle. The corresponding stability assessment is rigorous, and the efficient calculation method makes it readily implementable in CAD tools, thus allowing for circuit and device optimization. Results on three- and four-finger layouts are presented, including closed-form oscillation criteria for two-finger device

Spin-Hall Conductivity in Electron-Phonon Coupled Systems

We derive the ac spin-Hall conductivity $\sigma_{\rm sH}(\omega)$ of two-dimensional spin-orbit coupled systems interacting with dispersionless phonons of frequency $\omega_0$. For the linear Rashba model we show that the electron-phonon contribution to the spin-vertex corrections breaks the universality of $\sigma_{\rm sH}(\omega)$ at low-frequencies and provides a non-trivial renormalization of the interband resonance. On the contrary, in a generalized Rashba model for which the spin-vertex contributions are absent, the coupling to the phonons enters only through the self-energy, leaving the low frequency behavior of $\sigma_{\rm sH}(\omega)$ unaffected by the electron-phonon interaction.Comment: 4 pages, 3 figures, version as printe

Dynamic, self consistent electro-thermal simulation of power microwave devices including the effect of surface metallizations

We present an efficient simulation technique to account for the thermal spreading effects of surface metallizations in the self-consistent dynamic electro-thermal analysis of power microwave devices. Electro-thermal self-consistency is achieved by solving the coupled nonlinear system made of a temperature dependent device electrical model, and of an approximate description of the device thermal behavior through a thermal impedance matrix. The numerical solution is pursued in the frequency domain by the Harmonic Balance technique. The approach is applied to the thermal stability analysis of power AlGaAs/GaAs HBTs and the results show that metallizations have a significant impact on the occurrence of the device thermal collapse

Modeling of type-II quantum dot intermediate band solar cells accounting for thermal and optical intersubband transitions

Novel solar cell concepts relying on the use of nanostructures requires ad hoc device modeling tools able to cope with carrier transport and charge transfer mechanisms involving the host bulk material and the quantum confined states. In this work we apply such approach to study the implication of intersubband competitive processes in type-II GaSb/GaAs quantum dots on their application to intermediate band solar cells

Electron-phonon effects on spin-orbit split bands of two dimensional systems

The electronic self-energy is studied for a two dimensional electron gas coupled to a spin-orbit Rashba field and interacting with dispersionless phonons. For the case of a momentum independent electron-phonon coupling (Holstein model) we solve numerically the self-consistent non-crossing approximation for the self-energy and calculate the electron mass enhancement $m^*/m$ and the spectral properties. We find that, even for nominal weak electron-phonon interaction, for strong spin-orbit couplings the electrons behave as effectively strongly coupled to the phonons. We interpret this result by a topological change of the Fermi surface occurring at sufficiently strong spin-orbit coupling, which induces a square-root divergence in the electronic density of states at low energies. We provide results for $m^*/m$ and for the density of states of the interacting electrons for several values of the electron filling and of the spin-orbit interaction.Comment: 9 pages, 6 figures. Version as printe

Impact of carrier dynamics on the photovoltaic performance of quantum dot solar cells

The study presents a theoretical investigation of the impact of individual electron and hole dynamics on the photovoltaic characteristics of InAs/GaAs quantum dot solar cells. The analysis is carried out by exploiting a model which includes a detailed description of quantum dots (QD) kinetics within a drift-diffusion formalism. Steady-state and transient simulations show that hole thermal spreading across the closely spaced QD valence band states allows to extract the maximum achievable photocurrent from the QDs; on the other hand, slow hole dynamics turns QDs into efficient traps, impairing the short circuit current despite the extended light harvesting provided by the QDs