Plasmons and EELS
Lowloss spectroscopies, like those measurable with ElectronEnergy Loss (EELS) or by nonresonant Inelastic Xray Scattering (NIXS) are modern techniques to investigate the properties of matters, through the measurement of the inverse dielectric function $\varepsilon^{1}(\mathbf{q},\omega) $. The inverse dielectric function is the main result of a linear response calculation that can be carried out using Time Dependent Density Functional Theory (TDDFT) or in the manybody framework, via the BetheSalpeter Equation (BSE). In particular the latter, permits one to explicitely consider the excitonic effects, that can have a very important effects on semiconductors, insulators and in general in lowdimensional systems (see the research line on excitons).
One of the main features measurable by EELS or IXS are plasmons, collective excitations that can be understood in terms of classical electronic charge fluctuations. The Drude theory, for instance, gives already a very good estimate of the plasmon energy of a metal, in spite of being a completely classical approach (interestingly Sommerfeld later rederived the plasma oscillation formula using the correct FermiDirac distribution and quantum theory, to find exactly the same Drude formula). Plasmons, and in general the loss function, are related to the imaginary part of the inverse dielectric function. Goal of the group is to develop methods, approximations and numerical implementations in ab initio codes to analyse and predict scattering spectroscopy.
Links with highquality experiment are today possible, thanks to the high spatial and energy resolution of STEM electron microscope, or to the high momentumenergy resolution of the new generation synchrotron sources (ESRF, SOLEIL, etc.)
People Involved
Supporting Materials
Selected Bibliography

Lowenergy electronic excitations and bandgap renormalization in CuO (2017)

Interpretation of monoclinic hafnia valence electron energyloss spectra by timedependent density functional theory (2016)

Evidence for anisotropic dielectric properties of monoclinic hafnia using valence electron energyloss spectroscopy in highresolution transmission electron microscopy and ab initio timedependent densityfunctional theory (2014)

Highenergy collective electronic excitations in layered transitionmetal dichalcogenides (2014)

Exciton dispersion from first principles (2013)