arXiv subjects

Christoph Ringkamp

Publications and source records attributed to Christoph Ringkamp.

3 recordsLinked to original sources

arXiv2026

Kinetics-Driven Selective Stoichiometric Shift and Structural Asymmetry in $Bi_4Te_3$ Nanostructures for Hybrid Quantum Architectures

Advances in hybrid quantum architectures hinge on topological materials that can be synthesized with precise stoichiometric and structural control at the nanoscale. While $Bi_4Te_3$ is a promising candidate due to its dual topological phases, acting as both a strong topological insulator and a topological crystalline insulator, high-quality growth remains challenging due to a narrow stoichiometric window and high sensitivity to surface kinetics. Here, we establish a reproducible molecular beam epitaxy (MBE) process to produce stoichiometric, twin-free $Bi_4Te_3$ thin films with ultra-smooth surfaces and atomically sharp van der Waals stacks. By employing selective area epitaxy (SAE), we realize laterally confined $Bi_4Te_3$ nanostructures that exhibit a feature-dependent stoichiometric deviation. This phenomenon, which we term the selective stoichiometric shift, arises from the unequal lateral diffusion of Bi and Te adatoms, revealing a direct coupling between adatom kinetics and nanoscale compositional stability. Atomic-resolution imaging further uncovers asymmetric van der Waals gaps within the stacking sequence, identifying an intrinsic structural asymmetry between the quintuple and bilayer units. These findings provide fundamental insights into the crystallization of Bi_4Te_3$ and demonstrate a scalable route for integrating functional topological materials into next-generation superconducting hybrid quantum circuits.

cond-mat.mes-hall↗

arXiv2025

Robust Material Properties in Epitaxial In$_2$Te$_3$ Thin Films Across Varying Thicknesses

Sesqui-chalcogenides serve as a critical bridge between traditional semiconductors and quantum materials, offering significant potential in applications such as thermoelectrics, phase change memory, and topological insulators. While considerable attention has been focused on antimony- and bismuth-based compounds, characterized by substantial property changes upon reduction in film thickness, indium containing sesqui-chalcogenides like In$_2$Te$_3$ are emerging as promising candidates for photovoltaics and electronic devices. However, the effects of film thickness on the properties of In$_2$Te$_3$ remain largely unexplored. In this study, we investigate high-quality In$_2$Te$_3$ thin films grown by molecular beam epitaxy on Si(111) substrates across a thickness range from 2.7 nm to 24 nm. We employ X-ray diffraction, reflective high-energy electron diffraction and atomic force microscopy to analyze both the crystal structure and film morphology. Additionally, we utilize broadband optical spectroscopy alongside femtosecond pump-probe measurements and Raman spectroscopy to assess optical and vibrational properties, respectively. Our analysis reveals that material properties exhibit minimal dependence on film thickness, contrasting sharply with behavior observed in other chalcogenides such as Sb$_2$Te$_3$, Bi$_2$Se$_3$, or GeTe. This phenomenon can be attributed to covalent bonding present in In$_2$Te$_3$, which differs from those in its antimony- and bismuth-containing counterparts.

cond-mat.mtrl-sci↗

arXiv2025

Observation of angular momentum transfer among crystal lattice modes

Transfer of energy and linear momentum between lattice vibrations via anharmonic coupling is an important concept in solid-state physics. However, it remains difficult to directly observe how angular momentum is exchanged and conserved among lattice modes, even though these processes are thought to play an important role in achieving magnetization equilibrium and in spin relaxation effects like the Einstein-de Haas effect. Here, we demonstrate and coherently control angular momentum transfer between two lattice modes using the inverse process of anharmonic decay. The observed rotational phonon-phonon Umklapp scattering enforces the conservation of quantized crystal angular momentum, as dictated by the crystal's discrete rotational symmetry. We thereby experimentally confirm the fundamental analogy between linear and angular momentum conservation in solids. Moreover, we establish axial nonlinear phononics towards ultrafast control of material properties.

cond-mat.other↗