arXiv subjects

Mattia Benini

Publications and source records attributed to Mattia Benini.

3 recordsLinked to original sources

arXiv2025

Excitonic optical interface for GHz-THz collective excitations in a van der Waals magnet

Collective spin and lattice excitations in quantum materials span energy scales from GHz to THz, yet establishing a unified optical interface for these modes remains a central challenge. Here we show that excitonic resonances in the van der Waals antiferromagnet CrSBr provide a broadband optical interface for such excitations. Using femtosecond broadband transient reflectivity, we resolve coherent GHz magnon and THz phonon modes that modulate the dielectric response over a wide spectral range. Despite their distinct microscopic origin and frequency scales, both excitations give rise to the same emergent optical signature: a resonance at 1.46 eV that is absent in steady-state spectra and exhibits a characteristic {\pi}-phase inversion, identifying it as a discrete excitonic transition. We attribute this behaviour to boson-driven modulation of the dielectric response, which transiently transfers spectral weight from a nominally dark exciton into an observable channel without requiring a finite equilibrium oscillator strength. Supported by many-body calculations, we assign this feature to a higher-energy exciton with distinct momentum and orbital character and strongly suppressed optical matrix elements. These results establish excitonic resonances in van der Waals magnets as a platform for interfacing collective excitations across GHz, THz and optical frequency scales.

cond-mat.mtrl-sci↗

arXiv2025

Light-driven modulation of proximity-enhanced functionalities in hybrid nano-scale systems

Advancing quantum information and communication technology (qICT) requires smaller and faster components with actively controllable functionalities. This work presents a novel strategy for dynamically modulating magnetic properties via proximity effects controlled by light. We demonstrate this concept using hybrid nanoscale systems composed of C60 molecules proximitized to a cobalt metallic ferromagnetic surface, where proximity interactions are particularly strong. Our findings show that by inducing excitons in the C60 molecules with resonant ultrashort light pulses, we can significantly modify the interaction at the cobalt/C60 interface, leading to a striking 60% transient shift in the frequency of the dipolar ferromagnetic resonance mode of the Cobalt. This effect, detected via a specifically designed time-resolved magneto-optical Kerr effect (tr-MOKE) experiment, persists on a timescale of hundreds of picoseconds. Since this frequency shift directly correlates with a transient change in the anisotropy field (an essential parameter for technological applications) our findings establish a new paradigm for ultrafast optical control of magnetism at the nanoscale.

cond-mat.other↗

arXiv2025

Collapse of the standard ferromagnetic domain structure in hybrid Co/Molecule bilayers

We show that, upon the chemisorption of organic molecules, Co thin films display a number of unique magnetic properties, including the giant magnetic hardening and the violation of the Rayleigh law in magnetization reversal. These novel properties originate from the modification of the surface magnetic anisotropy induced by the molecule/film interaction: the π-d molecule/metal hybridization modifies the orbital population of the associated cobalt atoms and induces an additional and randomly oriented local anisotropy. Strong effects arise when the induced surface anisotropy is correlated over scales of a few molecules, and particularly when the correlation length of the random anisotropy field is comparable to the characteristic exchange length. This leads to the collapse of the standard domain structure and to the emergency of a glassy-type ferromagnetic state, defined by blurred pseudo-domains intertwined by diffuse and irregular domain walls. The magnetization reversal in such state was predicted to include topological vortex-like structures, successfully measured in this research by magnetic-force microscopy. Our work shows how the strong electronic interaction of standard components, Co thin films and readily available molecules, can generate structures with remarkable new magnetic properties, and thus opens a new avenue for the design of tailored-on-demand magnetic composites.

cond-mat.mtrl-sci↗