arXiv subjects

Christoph Krause

Publications and source records attributed to Christoph Krause.

3 recordsLinked to original sources

arXiv2026

Interplay between Aharonov-Bohm and Altshuler-Aronov-Spivak oscillations in phase-pure GaAs/InAs core/shell nanowires of different lengths

In GaAs/InAs core/shell nanowires, comprising a tubular conducting shell, interference phenomena observed under an axial field and originating from closed-loop states encircling the insulating core, provide an ideal platform for superconducting quantum devices that utilize effects such as Aharonov--Bohm or Altshuler--Aronov--Spivak-type conductance oscillations. Both effects are different in nature with respect to phase rigidity because of interference of non-time-reversed or time-reversed paths, respectively. Since their occurrence is largely governed by averaging effects, which depend on sample dimensions and the transport regime, we present a systematic study of flux-periodic oscillations of phase-pure zinc-blende GaAs/InAs core/shell nanowires as a function of gate voltage for samples with different contact separation lengths. Our analysis shows that with increasing contact separation length, averaging effects result in gradual reduction of $h/e$-periodic Aharonov--Bohm-type oscillations, while the $h/2e$-periodic Altshuler--Aronov--Spivak oscillations and its $h/4e$-periodic higher harmonics are enhanced. The additional phase rigidity seen in the $h/3e$-periodic oscillations is attributed to phase rigidity propagating from the neighbouring lower harmonics. Our tight-binding transport simulations on nanowires of different lengths which contain only a few scattering centers confirm the experimental observations regarding the different harmonics and their phase rigidity. Together, our experimental and simulation findings indicate quasi-ballistic transport with persistent Aharonov--Bohm-, and phase-rigid Altshuler--Aronov--Spivak-type oscillations despite few scattering centers.

cond-mat.mes-hall↗

arXiv2024

Two-dimensional photonic crystal cavities in ZnSe quantum well structures

ZnSe and related materials like ZnMgSe and ZnCdSe are promising II-VI host materials for optically mediated quantum information technology such as single photon sources or spin qubits. Integrating these heterostructures into photonic crystal (PC) cavities enables further improvements, for example realizing Purcell-enhanced single photon sources with increased quantum efficiency. Here we report on the successful implementation of two-dimensional (2D) PC cavities in strained ZnSe quantum wells (QW) on top of a novel AlAs supporting layer. This approach overcomes typical obstacles associated with PC membrane fabrication in strained materials, such as cracks and strain relaxation in the corresponding devices. We demonstrate the attainment of the required mechanical stability in our PC devices, complete strain retainment and effective vertical optical confinement. Structural analysis of our PC cavities reveals excellent etching anisotropy. Additionally, elemental mapping in a scanning transmission electron microscope confirms the transformation of AlAs into AlOx by post-growth wet oxidation and reveals partial oxidation of ZnMgSe at the etched sidewalls in the PC. This knowledge is utilized to tailor FDTD simulations and to extract the ZnMgSe dispersion relation with small oxygen content. Optical characterization of the PC cavities with cross-polarized resonance scattering spectroscopy verifies the presence of cavity modes. The excellent agreement between simulation and measured cavity mode energies demonstrates wide tunability of the PC cavity and proves the pertinence of our model. This implementation of 2D PC cavities in the ZnSe material system establishes a solid foundation for future developments of ZnSe quantum devices.

cond-mat.mtrl-sci↗

arXiv2024

Flux-periodic supercurrent oscillations in an Aharonov-Bohm-type nanowire Josephson junction

Phase winding effects in hollow semiconductor nanowires with superconducting shells have been proposed as a route to engineer topological superconducting states. We investigate GaAs/InAs core/shell nanowires with half-shells of epitaxial aluminium as a potential platform for such devices, where the thin InAs shell confines the electron wave function around the GaAs core. With normal contacts we observed pronounced $h/e$ flux periodic oscillations in the magnetoconductance, indicating the presence of a tubular conductive channel in the InAs shell. Conversely, the switching current in Josephson junctions oscillates with approximately half that period, i.e. $h/2e$, indicating transport via Andreev transport processes in the junction enclosing threading magnetic flux. On these structures, we systematically studied the gate-, field-, and temperature-dependent evolution of the supercurrent. Results indicate that Andreev transport processes can occur about the wire circumference indicating full proximitization of the InAs shell from the half-shell superconducting contacts.

cond-mat.mes-hall↗