Crystal elementary excitations, such as phonons, excitons and plasmons, and their momentum dispersions, are a fundamental topic in condensed matter physics. All these quasiparticles can be referred to as charged excitations, as they constitute the poles of the density-density response function $\chi$. Momentum-dependent electron energy-loss spectroscopy (q-EELS) has recently proven to be a pivotal tool for investigating charge excitations in suspended low-dimensional (2D) materials using a transmission electron microscope. In this seminar, I will discuss recent advances in the interpretation of low-momentum q-EELS measurements, along with advances in the calculation of electron-energy losses with manybody perturbation theory, required as electron interaction is enhanced in freestanding 2D materials. Such theoretical schemes are then applied to the study of the fine-structure exciton branch of monolayer hBN, then to the phonon dispersions and linewidths of graphene optical branches with excitonic effects near the Brillouin zone center ($\Gamma$) and corners (K), a regime relevant for transport graphene properties.
22/06/2026
Materials Science Seminar
22/06/2026 14:30 in Grassano Room Physics Department
TITLE:Many-Body Effects on Quasiparticles: from Excitons to Phonons in 2D Materials
Alberto Guandalini, Physics Dept. University of Rome “La Sapienza”