Speaker
Description
Tommaso Pincelli, Lawson T. Lloyd, Alessandro de Vita, Tania Mukherjee, Túlio de Castro, Amine Wahada, Roberto Sant$^a$, Srdjan Stavrič$^b$, Silvia Picozzi$^b$, Nathan P. Wilson$^c$, Zdeněk Sofer$^d$, Martin Wolf, Laurenz Rettig, Ralph Ernstorfer
$^a$Politecnico di Milano, Milano, Italy
$^b$Consiglio Nazionale delle Ricerche, Chieti, Italy
$^c$Walter Schottky Institute, Technische Universität München, Garching, Germany
$^d$Chemistry Department, University of Chemistry and Technology Prague, Prague, Czech Republic
We illustrate our results on CrSBr, Fe$_3$GeTe$_2$ (FGT), and CrI$_3$, exploring how spin order influences electronic band structure, exciton dynamics, and ultrafast magnetic processes in presence of strong vertical confinement of the electronic stats. We approach this problem by combining spectroscopic techniques, time-resolved experiments, and theoretical modeling: this provides a uniquely direct and momentum-resolved view of electronic properties and quasiparticle dynamics. We uncover a wealth of material-specific behaviors that underscore the potential of 2D spin-ordered systems for spintronic and optoelectronic applications.
In CrSBr, an air-stable, direct-gap semiconductor, exhibits in-plane FM and interlayer AFM ordering (T$_N$~132 K), which drive anisotropic electronic and optical properties. We identify strongly bound excitons (~700 meV) and track their dynamic with a fluence and wavelength-dependent experimental protocol. We are able to build a rate-equation model that quantitatively describes the entire dataset, pointing towards mechanisms of exciton-exciton annihilation rather than Mott transitions for the decay of the excitonic signal. We identify markers of spin order with promising potential for experiments linking magnetic and excitonic dynamics with wide ranging interest for optoelectronic and spintronic devices.
In FGT, a metallic van der Waals ferromagnet, comparison between trARPES experiments and DFT calculations unveil Stoner-like magnetic excitations and coherent oscillations at 3.69 THz, which we attribute to an A$_{1g}$ optical phonon at the Γ point. These findings reveal the complex spectrum of magnetic excitations in FGT as well as a strong coupling between magnetic and lattice dynamics, linking phonon modes to ultrafast demagnetization.
CrI$_3$, a van der Waals Ising ferromagnet, exhibits significant renormalization of the electronic band structure in the FM state. Resonant photoemission spectroscopy (ResPES) and X-ray absorption spectroscopy (XAS/XMCD) reveal a deviation from ionic character resulting from a hybridization between Cr 3d e$_g$ and I 5p orbitals, with DFT predictions corroborating experimental data. A picture of ligand-mediated FM ordering emerges that can be extended to the entire class of 2D Chromium chalcogenides, a key step in understanding the complex forms of magnetism emerging in reduced dimensionality systems.
