Many-Body physics at and out-of equilibrium

Research activity of the group of Andrea Marini, at the Institute of Material Science of the National Research Council, Italy

PNGF9 Progress of Non-Equilibrium Green’s functions – 9th edition

By in NEWS, Talks Tag ,

Villingen (Switzerland), 2026, 23-27 August

The 9th installment of the Progress of Non-Equilibrium Green’s functions (PNGF9) conference will take place at the Paul Scherrer Institute (PSI) in Switzerland.

The conference aims to bring together researchers directly involved in development and application of non-equilibrium Green’s functions (NGF) methods, as well as young researchers, who address recent developments, current challenges and future perspectives. PNGF9 will bridge theory developments, algorithmic and computational advances, ab-initio approaches, and modeling experiments at large-scale research facilities.

 

 

Frontiers in Ultrafast Phenomena in Quantum Materials

By in NEWS, Talks Tag , , , , , ,

Frascati (Italia), 2026, 21-24 April

The time–resolved angle–resolved photoemitton spectra of WSe, a paradigmatic metal dichalcogenide, is dominated by a peak that, initially observed withing the gap at the  valley, scatters, on an ultra–fast time scale of  fs to the S valley.
In his talk on April 24 at INFN Frascati National Laboratories, Andrea Marini questioned the commonly used interpretation of the experimental observations in terms of a massive bound electron–hole exciton scattering with phonon and behaving as a quasi–particle. By using a combined theoretical and experimental investigation he demonstrated that the observed dynamics can be interpreted as the photo–induced transition from a direct to and indirect excitonic insulating phase. The peaks that appear in the experimental spectrum correspond to single–particle levels renormalized by the excitonic spontaneous polarization.

book-of-abstracts Frascati 2026Download

Abstract

FAIR Data management of theoretical spectroscopy and green’s function methods

By in NEWS, Talks Tag , , , , , , , ,

Lausanne (Switzerland), 2026, 20-23 April

Electrons and phonons are basic concepts, considered as the most elemental and well defined example of fermions and bosons. So it may appear that their formal properties are clear and well established. In reality, despite books and reviews the theory of electron-phonon interaction(EPI) is still very much debated. The reason is mostly historical. Indeed the state-of-the art theoretical and numerical approach to the EPI has been built on top of two popular methods: model Hamiltonians and Density Functional Perturbation Theory (DFPT). These popular approaches have instilled two basic assumptions that are widely used in the literature and even coded in public Ab–Initio codes.

The first assumption is that the elemental EPI Hamiltonian is well approximated by using a statically screened interaction. 

The second assumption is clearly written in a recent Review of Modern Physics of F. Giustino where he writes that “the MBPT phonon self-energy is in agreement with the expression derived starting from time-dependent density-functional perturbation theory”.

In his talk, at CECAM (Centre Européen de Calcul Atomique et Moléculaire), on April 22-22, Andrea Marini disassembled the EPI Hamiltonian to demonstrate its stringent limitations. He also introduced a time-dependent formulation of DFPT showing how it can be exactly rewritten as the problem of a classical pendulum immersed in a quantistic liquid (semi-classical swing). He discussed the countless implications of such a problem linked the very basic foundations of MBPT.
Then he moved to present a formal an accurate derivation 3 of the dynamical screening of the EPI. In particular, he demonstrated that it is possible to derive an effective vertex correction function that can be easily defined using simple ingredients and used to amend calculations based on the statically screened approximation.

Program

FULL-BOOKLET_CECAM 2026_AprilDownload