Since 2016 Davide Sangalli is researcher at the Istituto di Struttura della materia (ISM -CNR), Division of Ultrafast Processes in Materials (FLASHit), Area della Ricerca di Roma 1, Monterotondo Scalo, Italy. He is presently CNR-PI for the PRIN project BIOX (Predicting and controlling the fate of bio-molecules driven by
extreme-ultraviolet radiation, prot. 20173B72NB). He is guest researcher at the Condensed Matter group of the Universtà degli Studi di Milano where he started a collaboration based on an agreement signed between the university and the ISM – CNR in 2019. He is also working within the MaX (Materials design at the eXascale H2020-EINFRA-2015-1, Grant Agreement No. 676598) and NFFA (Nanoscience Foundries and Fine Analysis – Europe H2020-INFRAIA-2014-2015, Grant Agreement No. 654360) projects. Davide Sangalli is one of the main developers of the yambo code also taking care of the administration of the yambo github repository.
Main research interests:
Many-Body physics from first principles: correlation effects in semiconductors and nanostructures.
Nonequilibrum physics and ultrafast phenomena: carrier dynamics, exciton dynamics, coherent dynamics, quantum kinetics, magnetization dynamics, transient spectroscopy.
Emergent physics in condensed matter. Berry-Phase, Kerr effect and Anomalous Hall effects in 3D materials; Kerr effect and valley physics in 2D materials; Gauge invariance out of equilibrium, Aharonov Bohm effect and excitonic insulator phase in 1D carbon nanotubes.
Development and exploitation of advanced first principles computational methods beyond density functional theory, mostly many-body perturbation theory, to study electronic and optical spectroscopies. Scientific software development and high-performance computing.
Exciton signature in pump and probe and exciton dynamics
One of the main research topics is the description and detection of excitons in pump and probe experiments on semi-conductors and insultors. While at equilibrium excitons can be detected in absorption experiments and angle resolver photo-emission (ARPES) is dominated by quasi-particles peaks, out of equilibrium excitons can be probed in time resolved (TR)-ARPES excitons. A laser pulse with energy resonant with the excitonic peak generates a coherent states which can be interpreted as a Bose-Einstein condensate (BEC) of excitons which leaves a clear fingerprint in TR-ARPES. This is shown in the image on the right, where the photo-emission from bulk lithium floride is represented after the action of a luser pulse resonant with the absorption of the 1s exciton. The exciton photoemission signal (upper panle) is a replica of the valence bend signal (lower panel) weighted by the excitonic wave–function. The distance from the conduction band minima corresponds to the binding energy of the exciton. Data from PRM 3, 124601 (2020)
An open research field is the description of how such coherent excitonic state can evolve into non coherent excitonic population and later evolve under the action of exciton-phonon, exciton-exciton and exciton-photon processes.
Davide Sangalli moved at the ISM in Montelibretti within the FIRB projec FLASH-IT, whose aim is the first principles description of out-of-equilibrium dynamics of electrons in the ultra-short (atto/femto-second) time domain. The work is done in close collaboration with the experimental group of the Politecnico di Milano.
Here on the top left a representation of the electrons and holes occupations on the band structure of bulk silicon at different time snapshots after the action of an ultra-short laser pulse. Data from EPL 110, 47004 (2015). On the top right a representation of the electron-phonon lifetimes (values in meV) responsible for the dynamics shown on the left. Finally a link to a short video of the carriers dynamics in silicon due to electron-phonon and electron-electron lifetimes ELEL+ELPH_2ps
On the right the transient reflectivity signal of bulk silicon, computed at the Bethe-Salpeter, level due o the non-equilibrium carriers distribution at 200 fs from the maximum of the laser pulse. Data from Phys. Rev. B 93, 195205 (2016). The results of the simulations are directly compared with the signal collected in Milano.
At the end of the page an invited talk at the MaX conference held in Trieste, January 2018, where these results are presented.
ab initio study of Fe doped ZrO2 and development of the magneto optical Kerr effect (First post-doc fellow, 2011 – 2013):
After the PhD he worked at the Laboratorio MDM (IMM – CNR) within the OSEA project (Cariplo fundings) carrying on first principles simulations of dilute magnetic semiconductor, iron doped zirconia in particular. He also had an active role in the experimental characterization, with XPS measurements of iron doped films, directly comparing the results with the first principles simulated electronic structures. In the same time he kept his interest in the description of absorption spectra, studying fundamental aspects of the magneto-optical Kerr effect (MOKE). The MOKE has been implemented in the yambo code with the possibility to include local fields and excitonic effects, thus extending the BSE implementation to the spinorial formalism. The same implementation has been provided a key tool for the description of the optical properties of the MoS2 system.
Master thesis and PhD (2007 – 2011)
Since his master thesis (2007) Davide Sangalli worked on the development of first principles codes, extending the TDDFT implementation in the Abinit code to the description of spin-polarized systmes. He the started his PhD in Rome, CNISM grant (2007-2010), working on the effects of many body correlation in the absorption spectra (visible/UV range) of correlated materials. During the PhD he also described, from first-principles, the Aharonov-Bohm effect in carbon nanotubes, having implemented the effect of a magnetic field in the self-consistent module of the yambo code and, finally, he worked, in close collaboration with an experimental group of the Università degli studi di Milano, to the description of linear chains of carbon embedded in a pure-carbon systems.
Available lectures / seminars:
- Pump and Probe Experiments from First Principles, Max Conference, 1st February 2018
- Real-time Many-Body simulation: propagating the density matrix, Computational School on Electronic Excitations in Novel Materials Using the Yambo Code, 29th January 2020