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Marco Grioni was born in Milan (Italy) where he graduated in 1982. He has occupied research positions at Minneapolis (USA), Nijmegen (The Netherlands), Orsay (France) and Neuchâtel, where he became Privat Docent in Solid State Physics in 1994. Since 1996 he is at EPFL, where he teaches physics to undergraduate and graduate students. He is acting director of the Laboratory of Electron Spectroscopy of IPN, and an adjunct professor from 2005.

His research interests concern the electronic properties of novel materials,namely high-temperature superconductors, low-dimensional metals, and heavy fermion compounds, which he investigates by high-resolution photoemission (ARPES), ultrafast time-resolved ARPES, and photon-in photon-out synchrotron-based spectroscopies. Author of approx. 220 scientific articles, he is actively involved in the development of new instruments. From 2003 to 2006 he was the chairman of the users organization of the European Synchrotron Radiation Facility (ESRF Grenoble). Between 2010 and 2017 he served as chairman of the scientific advisory committee of the french national synchrotron light source SOLEIL

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Angle-resolved photoemission spectroscopy

Angle-resolved photoemission spectroscopy (ARPES) is an experimental technique used in condensed matter physics to probe the allowed energies and momenta of the electrons in a material, usually a cr

Electronic band structure

In solid-state physics, the electronic band structure (or simply band structure) of a solid describes the range of energy levels that electrons may have within it, as well as the ranges of energy th

Electronic structure

In physics, electronic structure is the state of motion of electrons in an electrostatic field created by stationary nuclei. The term encompasses both the wave functions of the electrons and the ene

Hidden bulk and surface effects in the spin polarization of the nodal-line semimetal ZrSiTe

Helmuth Berger, Alberto Crepaldi, Mauro Fanciulli, Gianmarco Gatti, Daniel Gosalbez Martinez, Marco Grioni, Arnaud Magrez, Oleg Yazyev

Local inversion symmetry breaking in centrosymmetric materials can lead to large spin polarization of the electronic band structure in separate sectors of the unit cell. Here, the authors reveal such hidden spin polarisation in ZrSiTe using spin and angle resolved photoemission spectroscopy in combination with ab initio band structure calculations and investigate the resultant spin polarised bulk and surface properties In non-magnetic materials the combination of inversion symmetry breaking (ISB) and spin-orbit coupling (SOC) determines the spin polarization of the band structure. However, a local spin polarization can also arise in centrosymmetric crystals containing ISB subunits. This is namely the case for the nodal-line semimetal ZrSiTe where, by combining spin- and angle-resolved photoelectron spectroscopy with ab initio band structure calculations, we reveal a complex spin polarization. In the bulk, the valence and conduction bands exhibit opposite spin orientations in two spatially separated two-dimensional ZrTe sectors within the unit cell, yielding no net polarization. We also observe spin-polarized surface states that are well separated in energy and momentum from the bulk bands. A layer-by-layer analysis of the spin polarization allows us to unveil the complex evolution of the signal in the bulk states near the surface, thus bringing the intertwined nature of surface and bulk effects to the fore.

NATURE RESEARCH2021

Evidence of Large Polarons in Photoemission Band Mapping of the Perovskite Semiconductor CsPbBr3

Thomas Roland Barillot, Majed Chergui, Nicola Colonna, Alberto Crepaldi, Gianmarco Gatti, Marco Grioni, Nicola Marzari, Serhii Polishchuk, Matthias Wolf

Lead-halide perovskite (LHP) semiconductors are emergent optoelectronic materials with outstanding transport properties which are not yet fully understood. We find signatures of large polaron formation in the electronic structure of the inorganic LHP CsPbBr3 by means of angle-resolved photoelectron spectroscopy. The experimental valence band dispersion shows a hole effective mass of 0.26 +/- 0.02 m(e), 50% heavier than the bare mass m(0) = 0.17 m(e) predicted by density functional theory. Calculations of the electron-phonon coupling indicate that phonon dressing of the carriers mainly occurs via distortions of the Pb-Br bond with a Frohlich coupling parameter alpha = 1.81. A good agreement with our experimental data is obtained within the Feynman polaron model, validating a viable theoretical method to predict the carrier effective mass of LHPs ab initio.

AMER PHYSICAL SOC2020

Insight into the electronic structure of semiconducting epsilon-GaSe and epsilon-InSe

Helmuth Berger, Alberto Crepaldi, Marco Grioni, Daniela Pacilè

Metal monochalcogenides (MX) have recently been rediscovered as two-dimensional materials with electronic properties highly dependent on the number of layers. Although some intriguing properties appear in the few-layer regime, the carrier mobility of MX compounds increases with the number of layers, motivating the interest in multilayered heterostructures or bulk materials. By means of angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory calculations, we compare the electronic band structure of bulk epsilon-GaSe and epsilon-InSe semiconductors. We focus our attention on the top valence band of the two compounds along main symmetry directions, discussing the effect of spin-orbit coupling and contributions from post-transition-metal (Ga or In) and Se atoms. Our results show that the top valence band at Gamma point is dominated by Se p(z) states, while the main effect of Ga or In appears more deeply in binding energy, at the Brillouin zone corners, and in the conduction band. These findings explain also the experimental observation of a hole effective mass rather insensitive to the post-transition metal. Finally, by means of spin-resolved ARPES and surface band structure calculations we describe Rashba-Bychkov spin splitting of surface states in epsilon-InSe.

AMER PHYSICAL SOC2020