arXiv subjects

Richard Leven

Publications and source records attributed to Richard Leven.

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

Momentum-Resolved Electronic Structure and Orbital Hybridization in the Layered Antiferromagnet CrPS$_4$

Chromium thiophosphate (CrPS$_4$) is a layered two-dimensional antiferromagnetic semiconductor exhibiting intriguing spintronic and magneto-optical properties, yet its electronic band structure has remained experimentally uncharacterized. Here, we employ momentum-resolved photoemission spectroscopy above and below the N\'eel temperature, complemented by density functional theory with Hubbard U corrections (DFT+U), to reveal a valence band dominated by Cr $3d$ and S $3p$ states with a ligand-to-metal charge-transfer band gap. We identify weakly hybridized t$_{2g}$ orbitals responsible for magnetic ordering and strongly hybridized e$_{g}$ orbitals that relax dipole selection rules, enabling optically active orbital transitions. These findings establish a foundational understanding of CrPS$_4$'s electronic structure, providing a benchmark for theoretical models and informing future investigations into its orbital physics and potential device applications.

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↗