arXiv subjects

Fabian Göhler

Publications and source records attributed to Fabian Göhler.

6 recordsLinked to original sources

arXiv2026

Spin- and Angle-resolved Photoelectron Spectroscopy Study of the Quantum Spin Hall Insulator Bismuthene and its Precursor Phase

Recent studies have revealed that a confined bismuth layer at the graphene/SiC interface can be reversibly switched between a topologically trivial precursor phase and the quantum spin Hall insulator bismuthene. Here, we present a detailed spin- and angle-resolved photoelectron spectroscopy study of both structures, resolving the spin texture of their low-energy electronic states. Owing to the strong intrinsic spin-orbit coupling of bismuth and the asymmetric confinement potential at the interface, the valence bands of both structures are Rashba-split. We demonstrate the expected spin-momentum locking for both phases and Kramers' doublets through the investigation of the valence bands' spin polarization at multiple positions in reciprocal space.

cond-mat.mtrl-sci↗

arXiv2026

Disentangling bulk and surface states in the electronic structure of PtBi$_2$(0001)

Recent reports of surface-localized topological superconductivity in trigonal PtBi$_2$ highlight the importance of understanding its surface electronic structure. We investigate the bulk and surface band structure of PtBi$_2$ using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. Through photon-energy- and polarization-dependent measurements, we disentangle bulk dispersions from surface states on the two distinct surface terminations of PtBi$_2$(0001). For both terminations, we assign several different surface states and find good agreement between experiment and calculations. Based on our calculations, we analyze the orbital composition in the surface and bulk bands and compare the results to polarization-dependent ARPES measurements. Together, our results provide a coherent picture of the surface electronic structure of PtBi$_2$ across both surface terminations.

cond-mat.str-el↗

arXiv2026

Fermiology and spin polarization of topological surface states in PtBi$_2$

Layered PtBi$_2$ is a candidate for topological superconductivity arising in Fermi-arc surface states. Using spin- and angle-resolved photoemission spectroscopy, we demonstrate that the Fermi arcs in PtBi$_2$ are singly degenerate and spin-polarized, which establishes their nontrivial topology and constitutes a necessary condition for topological superconductivity. We further uncover a pronounced surface-termination dependence of the Fermi-arc dispersion, yielding either nearly flat or approximately linear bands in agreement with first-principles calculations. Together, the observed spin polarization and termination-dependent bandwidth of the Fermi-arc surface states identify key ingredients underlying the potential emergence of topological superconductivity in PtBi$_2$.

cond-mat.supr-con↗

arXiv2025

Si Intercalation Beneath Epitaxial Graphene: Modulating Mott States at the SiC(0001) Interface

Intercalation has proven to be a powerful tool for tailoring the electronic properties of freestanding graphene layers as well as for stabilizing the intercalated material in a two-dimensional configuration. This work examines Si intercalation of epitaxial graphene on SiC(0001) using three preparation methods. Dangling bond states at the interface were found to undergo a Mott-Hubbard metal-insulator transition as a result of a significant on-site repulsion. Comparing this heterostructure consisting of graphene and a Mott insulator with a similar system without graphene, reveals the screening ability of graphene's conduction electrons on the on-site repulsion. The system presented here can serve as a template for further research on Mott insulators with variable band gap.

cond-mat.mtrl-sci↗

arXiv2025

Solving the Phase Problem of Diffraction: X-ray Standing Waves Imaging on Bismuthene/SiC(0001)

The phase retrieval problem is a fundamental shortcoming of all diffraction-based methods, arising from the inability to measure the phase of scattered waves. The (normal incidence) X-ray standing wave (NIXSW) technique circumvents this issue by introducing a (Bragg-generated) X-ray standing wave field throughout the sample, relative to which any atomic species can be localized by probing its fluorescence or photoelectron yield. In essence, in a single measurement the complex scattering factor (i.e., its amplitude \textit{and} phase) corresponding to the used Bragg reflection is determined. Performing this for multiple Bragg reflections enables one to reconstruct the scattering density of the sample in three dimensions, straightforwardly as the Fourier sum of all measured (complex) scattering factors. Here, we utilize this technique to reveal the structural key features involved in the formation of the quantum spin Hall insulator bismuthene on silicon carbide. In this prominent example, the two-dimensional Bi layer is confined between a 4H-SiC substrate crystal and an epitaxial graphene layer. The key finding is a change in the adsorption site of the Bi atoms underneath the graphene upon hydrogenation, caused by the H-saturation of one (out of three) Si dangling bonds per unit cell. This structural change, clearly revealed by our NIXSW imaging experiment, is the key feature leading to the formation of the characteristic band structure of the 2D bismuthene honeycomb.

cond-mat.mes-hall↗

arXiv2025

Reversible Switching of the Environment-Protected Quantum Spin Hall Insulator Bismuthene at the Graphene/SiC Interface

Quantum Spin Hall Insulators (QSHI) have been extensively studied both theoretically and experimentally because they exhibit robust helical edge states driven by spin-orbit coupling and offer the potential for applications in spintronics through dissipationless spin transport. However, to realize devices, it is indispensable to gain control over the interaction of the active layer with the substrate, and to protect it from environmental influences. Here we show that a single layer of elemental Bi, formed by intercalation of an epitaxial graphene buffer layer on SiC(0001), is a promising candidate for a QSHI. This layer can be reversibly switched between an electronically inactive precursor state and a ``bismuthene state'', the latter exhibiting the predicted band structure of a true two-dimensional bismuthene layer. Switching is accomplished by hydrogenation (dehydrogenation) of the sample, i.e., a partial passivation (activation) of dangling bonds of the SiC substrate, causing a lateral shift of Bi atoms involving a change of the adsorption site. In the bismuthene state, the Bi honeycomb layer is a prospective QSHI, inherently protected by the graphene sheet above and the H-passivated substrate below. Thus, our results represent an important step towards protected QSHI systems beyond graphene.

cond-mat.mes-hall↗