arXiv subjects

Kilian Strauß

Publications and source records attributed to Kilian Strauß.

4 recordsLinked to original sources

arXiv2026

Experimental realization of the minimal two-dimensional multi-orbital kagome model

Kagome materials have emerged as a major platform for correlated and topological quantum matter, hosting flat bands, Dirac dispersions and van Hove singularities rooted in frustrated lattice geometry. While their essential physics is epitomized by the canonical single-orbital kagome model, real kagome materials are intrinsically multi-orbital and typically chemically and structurally complex, with additional three-dimensional coupling making kagome geometry and orbital degrees of freedom difficult to disentangle. Here we realize a truly two-dimensional, elemental two-orbital kagome system in monolayer Sb on SiC(0001). Substrate-induced orbital filtering isolates the in-plane Sb p_x/p_y orbitals into a six-band kagome manifold, establishing a chemically simple, minimal platform for multi-orbital kagome physics. We demonstrate two consequences that distinguish this system from the canonical single-orbital model. First, chemically enforced half filling pins the Fermi level to a closed nodal line, whose finite density of states drives a unit-cell-conserving breathing instability and opens a giant insulating gap. Second, we uncover orbital-resolved atomic obstruction: individual orbital-derived manifolds realize obstructed atomic limits, whereas their combined half-filled valence manifold is non-obstructed. Our results establish kagome antimonene as a benchmark system for exploring orbital-driven electronic, structural and topological kagome physics in the genuine two-dimensional limit.

cond-mat.mtrl-sci↗

arXiv2026

Enhanced Screening in Epitaxial Graphene via Nearly Free-Electron Metal Intercalation

Graphene exhibits extraordinarily high carrier mobility, making it a promising platform for next-generation electronics. Scalable growth on SiC, however, suffers from limited dielectric screening at the graphene-substrate interface, degrading electronic performance. In this work, we systematically enhance dielectric screening by intercalating a bilayer of indium at the graphene-SiC interface. Using graphene's plasmaronic signature observed in angle-resolved photoemission spectroscopy as a proxy for interaction strength, we quantitatively demonstrate strong dielectric screening arising from the interplay of both indium layers. Layer-resolved density functional theory shows that the first indium layer acts as a buffer that absorbs substrate interactions, enabling the second layer to form a nearly free-electron system that efficiently screens the graphene layer above. Experiments with only a single intercalated indium layer reveal reduced screening, confirming the essential role of the second layer. Our results establish 2ML indium intercalation as a powerful route for engineering dielectric environments in graphene.

cond-mat.mtrl-sci↗

arXiv2026

Resonantly-enhanced Raman response in graphene-capped bismuthene on SiC

Two-dimensional quantum spin Hall insulators based on atomic monolayers offer a promising route toward dissipationless electronics, yet their practical use is often limited by environmental instability. Encapsulating the system with a graphene capping layer has been shown to be a reliable method to prevent oxidation and degradation. However, the confirmation of a successful encapsulation still relies on ultra-high vacuum techniques, that considerably slow the process. Here, we present an ex situ, rapid, nondestructive and spatially resolved Raman characterization of graphene-capped bismuthene, a honeycomb monolayer of Bi on SiC. A pronounced Raman scattering peak at around 122 cm-1 is identified as the E2g phonon of bismuthene, via a comparison with density functional perturbation theory calculations. We use excitation-energy and polarization-dependent Raman measurements to enable an unambiguous assignment of the spectral features. Tuning the excitation energy close to the excitonic transition in pristine bismuthene, we observe a strong enhancement of the Raman response and the emergence of additional scattering peaks. In this regime, higher-order phonon features, as well as interfacial modes between bismuthene and the SiC substrate, become visible, suggesting the involvement of resonant scattering processes. Our results establish Raman micro-spectroscopy as a versatile tool for probing graphene-protected quantum materials, providing access to lattice dynamics and interlayer coupling.

cond-mat.mtrl-sci↗

arXiv2025

Competing excitonic couplings as origin of mimicked phase transitions in zinc-phthalocyanine single crystals

The optical properties of molecular crystals are largely determined by the excitonic coupling of neighboring molecules. This coupling is extremely sensitive to the arrangement of adjacent molecular units, as their electronic interaction is defined by the relative orientation of the individual transition dipole moments and their wave function overlap. Hence, the optical properties, such as fluorescence, are usually highly anisotropic and good indicators of structural changes during the variation of intensive thermodynamic parameters like temperature or pressure. Here, we discuss the peculiar though archetypical case of $β$-phase zinc-phthalocyanine: In single crystals, we report a sudden change of spectral emission with temperature from a broad, unpolarized Frenkel-exciton type luminescence to a narrow, highly polarized superradiance-like fluorescence below 80 K. Surprisingly, we find that there is no sign of a discrete structural phase transition in this temperature regime. To understand this apparent contradiction, we perform polarization-, temperature- and time-dependent photoluminescence measurements along different crystallographic directions to fully map the emission characteristics of the crystal-exciton. By means of ab-initio calculations on a density functional theory level we conclude that our observations are consistent with a dimer exciton model when considering thermalized electronic states. As such, our study presents a representative case study on a well-established molecular material class demonstrating that caution is advised when attributing discrete changes in electronic observables to a structural phase transition. As we show for zinc-phthalocyanine in its $β$-phase modification, slowly varying excitonic couplings and thermal redistribution of excitations can mimic the same signatures attributed to a structural phase transition.

cond-mat.mtrl-sci↗