Thorsten Deilmann

Image-potential surface states are simple model systems, where spin-dependent effects can be studied in view of spintronic applications. The Rashba effect in surface states at high- Z materials is related to both the strong spin-orbit interaction in heavy atoms and the orbital angular momentum arising from the inversion-symmetry breaking at the surface. Our study on image-potential states at Bi 2 Se 3 and Bi 2 Te 3 showcases that the orbital angular momentum causes an intrinsically reversed Rashba parameter α R ≈ − 100 meV Å , i.e., a reversed spin splitting compared with the prototypical Rashba-split Au(111) crystal-induced surface state. We present a consistent picture of spin-resolved experimental data from inverse photoemission and three-photon photoemission together with calculations from density-functional theory and many-body perturbation theory.

We investigate the adsorption geometry, binding energetics, and electronic structure of the polycyclic aromatic hydrocarbons benzene, naphthalene, and anthracene on a monolayer of MoS 2 using first-principles calculations. Structural relaxations are performed within density functional theory (DFT) including corrections for van der Waals interactions. Quasiparticle electronic structures are subsequently obtained using many-body perturbation theory employing the GW approximation. All three molecules preferentially adsorb flat above sulfur sites of the MoS 2 surface and form type-I heterojunctions with MoS 2 . Only anthracene exhibits weak hybridization with the MoS 2 valence band maximum (VBM) and VBM-1, leading to a slight reduction of the MoS 2 valence band splitting. The HOMO-LUMO (highest occupied molecular orbital, lowest unoccupied molecular orbital) gaps of the molecules are substantially reduced by the dielectric screening of the MoS 2 substrate. These results highlight the asymmetric role of screening and hybridization in MoS 2 -organic hybrid systems and provide insight into band alignment and electronic structure engineering for molecularly functionalized two-dimensional semiconductors.

Twisted bilayers of transition metal dichalcogenides (TMDC) form moiré superlattices hosting localized excitons and enabling access to Mott-Hubbard physics by the formation of moiré minibands. However, their electronic properties are highly sensitive to twist angle fluctuations, disorder, and lattice reconstructions, making fast and noninvasive local characterization challenging. Here, we correlate twist angle variations in twisted WSe₂ bilayers across micrometer length scales using lateral force microscopy (LFM) and micro-Raman spectroscopy. We reveal twist angle variations exceeding 1° across optically and transport-relevant length scales. For twist angles in the range 3° < α < 12°, distinct Raman signatures from optical moiré phonons enable high-precision twist angle determination with sub-micrometer spatial resolution under ambient conditions. Our approach achieves a precision better than ± 0.3° particularly in the low-twist angle regime relevant for correlation physics and is applicable to hBN-encapsulated heterostructures, establishing micro-Raman spectroscopy as a rapid, noninvasive tool for twist angle screening.

Triggered by advances in atomic-layer exfoliation and growth techniques, along with the identification of a wide range of extraordinary physical properties in self-standing films consisting of one or a few atomic layers, two-dimensional (2D) materials such as graphene, transition metal dichalcogenides (TMDs), and other van der Waals (vdW) crystals now constitute a broad research field expanding in multiple directions through the combination of layer stacking and twisting, nanofabrication, surface-science methods, and integration into nanostructured environments. Photonics encompasses a multidisciplinary subset of those directions, where 2D materials contribute remarkable nonlinearities, long-lived and ultraconfined polaritons, strong excitons, topological and chiral effects, susceptibility to external stimuli, accessibility, robustness, and a completely new range of photonic materials based on layer stacking, gating, and the formation of moiré patterns. These properties are being leveraged to develop applications in electro-optical modulation, light emission and detection, imaging and metasurfaces, integrated optics, sensing, and quantum physics across a broad spectral range extending from the far-infrared to the ultraviolet, as well as enabling hybridization with spin and momentum textures of electronic band structures and magnetic degrees of freedom. The rapid expansion of photonics with 2D materials as a dynamic research arena is yielding breakthroughs, which this Roadmap summarizes while identifying challenges and opportunities for future goals and how to meet them through a wide collection of topical sections prepared by leading practitioners.

The optical properties of layered materials are dominated by intralayer excitons; especially for layered antiferromagnets the layer-to-layer charge hopping, and therefore interlayer excitons, are spin forbidden. An external magnetic field, however, can continuously drive the magnetic order towards layer-to-layer ferromagnetic, which opens spin-allowed charge-transfer channels between the layers. Here, we elaborate how their admixture changes the composition and nature of the excitons, leading to an extension over many layers, and causing a quadratic redshift with respect to the external magnetic field in CrSBr. We present a minimal four-band model to elucidate the interplay between the various interaction and coupling mechanisms which is able to reproduce the findings of our G W –Bethe-Salpeter equation calculations as a function of magnetic field. Our model is generally valid for any coupled layers with different spin directions and the insights help to systematically address excitons and to predict their optical signatures in such systems.