arXiv subjects

Bernd Kästner

Publications and source records attributed to Bernd Kästner.

3 recordsLinked to original sources

arXiv2026

Generation of an anomalous linearly dispersing spin-polarized band in Bi-based topological insulators

We report the generation of an anomalous linearly dispersing, spin-polarized band in Bi-based topological insulator (TI) thin films, induced by soft Ar-ion bombardment followed by annealing. This extra band -- which we call the anomalous linearly dispersing state (ALS) -- is superimposed on the regular band structure including the topological surface state (TSS), spans an unusually large energetic range of up to ${\sim}\,\SI{650}{\milli\electronvolt}$ at the $Γ$-point, and appears near the Fermi energy. Spin-resolved measurements indicate spin-momentum locking with a helicity \emph{opposite} to that of the regular TSS. The Fermi velocity of the ALS, $v_\mathrm{F} = (5.1\pm 0.4)\times 10^{5}\,\frac m s$, is indistinguishable from that of the regular TSS, $(5.3\pm 0.5)\times 10^{5}\,\frac m s$. The observation is reproducible across samples of varying thickness and was confirmed at two independent synchrotron radiation facilities. We discuss different mechanisms for the physical origin of the observed ALS including sputtering-induced TSS relocation, bi-layer formation by,e.g., chalcogen removal, and high-index surface relocation.

cond-mat.mtrl-sci↗

arXiv2022

Assessment of sub-sampling schemes for compressive nano-FTIR imaging

Nano-FTIR imaging is a powerful scanning-based technique at nanometer spatial resolution which combines Fourier transform infrared spectroscopy (FTIR) and scattering-type scanning near-field optical microscopy (s-SNOM). However, recording large spatial areas with nano-FTIR is limited by long measurement times due to its sequential data acquisition. Several mathematical approaches have been proposed to tackle this problem. All of them have in common that only a small fraction of randomly chosen measurements is required. However, choosing the fraction of measurements in a random fashion poses practical challenges for scanning procedures and does not lead to time savings as large as desired. We consider different, practically relevant sub-sampling schemes assuring a faster acquisition. It is demonstrated that results for almost all considered sub-sampling schemes, namely original Lissajous, triangle Lissajous, and random reflection sub-sampling, at a sub-sampling rate of 10%, are comparable to results when using a random sub-sampling of 10%. This implies that random sub-sampling is not required for efficient data acquisition.

physics.optics↗

arXiv2014

Partitioning of on-demand electron pairs

We demonstrate the high fidelity splitting of electron pairs emitted on demand from a dynamic quantum dot by an electronic beam splitter. The fidelity of pair splitting is inferred from the coincidence of arrival in two detector paths probed by a measurement of the partitioning noise. The emission characteristic of the on-demand electron source is tunable from electrons being partitioned equally and independently to electron pairs being split with a fidelity of 90%. For low beam splitter transmittance we further find evidence of pair bunching violating statistical expectations for independent fermions.

cond-mat.mes-hall↗