Electronic thermal conductivity of disordered metals

We calculate the thermal conductivity of interacting electrons in disordered metals. In our analysis we point out that the interaction affects thermal transport through two distinct mechanims, associated with quantum interference corrections and energy exchange of the quasi particles with the electromagnetic environment, respectively. The latter is seen to lead to a violation of the Wiedemann-Franz law. Our theory predicts a strong enhancement of the Lorenz ratio $\kappa /\sigma T$ over the value which is predicted by the Wiedemann-Franz law, when the electrons encounter a large environmental impedance.Comment: 4 page

Gli hedge fund – Rendimento, rischio e valutazione della performance

Gli hedge fund hanno origine negli Stati Uniti negli anni cinquanta e mirano a realizzare performance positive indipendentemente dai trend dei mercati finanziari. La possibilità di conseguire rendimenti elevati, anche in periodi sfavorevoli deriva dall’elevato grado di libertà lasciato ai gestori nell’uso della leva finanziaria e di strumenti derivati con finalità sia speculative che di copertura. Dopo aver trattato il tema del profilo rendimento-rischio tipico degli hedge fund, il focus del lavoro è centrato sulle metodologie più innovative di misurazione e valutazione delle performance, ponendo particolare attenzione all’efficienza degli indici di categoria più diffusi nel mercato. A supporto dell’analisi teorica, è stata realizzata una verifica empirica su un campione significativo di fondi e indici di settore. Il lavoro si sofferma infine sul tema dell’ottimizzazione dal punto di vista economico e finanziario di portafogli di strumenti alternativi, alla luce dell’evoluzione della letteratura e della prassi invalsa in materia

Management Styles of Italian Equity Mutual Funds

working paper n.1

Phonon-Mediated Coupling of InGaAs/GaAs Quantum-Dot Excitons to Photonic Crystal Cavities

We demonstrate that the emission characteristics of site-controlled InGaAs/GaAs single quantum dots embedded in photonic crystal slab cavities correspond to single confined excitons coupled to cavity modes, unlike previous reports of similar systems based on self-assembled quantum dots. By using polarization-resolved photoluminescence spectroscopy at different temperatures and a theoretical model, we show that the exciton-cavity interaction range is limited to the phonon sidebands. Photon-correlation and pump-power dependence experiments under nonresonant excitation conditions further establish that the cavity is fed only by a single exciton

Perfect energy-feeding into strongly coupled systems and interferometric control of polariton absorption

The ability to drive a system with an external input is a fundamental aspect of light-matter interaction. The key concept in many photonic applications is the 'critical coupling' condition(1,2): at criticality, all the energy fed to the system is dissipated within the system itself. Although this idea was crucial to enhance the efficiency of many devices, it was never considered in the context of systems operating in a non-perturbative regime. In this so-called strong-coupling regime, the matter and light degrees of freedom are mixed into dressed states, leading to new eigenstates called polaritons(3-10). Here we demonstrate that the strong-coupling regime and the critical coupling condition can coexist; in such a strong critical coupling situation, all the incoming energy is converted into polaritons. A general semiclassical theory reveals that such a situation corresponds to a special curve in the phase diagram of the coupled light-matter oscillators. In the case of a system with two radiating ports, the phenomenology shown is that of coherent perfect absorption (CPA; refs 11,12), which is then naturally understood in the framework of critical coupling. Most importantly, we experimentally verify polaritonic CPA in a semiconductor-based intersubband-polariton photonic crystal resonator. This result opens new avenues in polariton physics, making it possible to control the pumping efficiency of a system independent of the energy exchange rate between the electromagnetic field and the material transition