arXiv subjects

Daniel Stoffels

Publications and source records attributed to Daniel Stoffels.

3 recordsLinked to original sources

arXiv2026

Electrical manipulation of oxygen stoichiometry in multiterminal YBa$_2$Cu$_3$O$_{7-\delta}$ junctions

Local manipulation of oxygen stoichiometry offers a route to control the electronic properties of complex oxides, yet the selective modification of individual current-carrying branches through oxygen redistribution remains unexplored in multiterminal high-temperature superconducting junctions. In a YBa$_2$Cu$_3$O$_{7-\delta}$ Y-shaped three-terminal device, we demonstrate the possibility to electrically control oxygen vacancy migration on a hand-picked terminal while largely preserving the other two. Oxygen-depleted propagating fronts are directly visualized by the resulting change in optical reflectivity and they are linked to the evolution of the electrical response. The process is highly directional and determined by the polarity of the applied current, allowing for the creation of either a converging or a diverging propagating front from the central node of the Y-shaped device. The associated changes in resistance exhibit relaxation on a timescale of minutes, driven by the vacancy concentration gradient. Effects of oxygen migration are also mapped by Kelvin Probe Force Microscopy and Scanning Laser Microscopy, which probe work-function changes and spatially resolved variations in the superconducting transition, respectively. Notably, the Tc contrast revealed by the latter provides a quantitative handle on the underlying oxygen content, enabling direct visualization of oxygen redistribution. Finite-element modeling and nanoprobe X-ray diffraction qualitatively reproduce the observed vacancy redistribution. These results establish a post-fabrication route to locally tune properties of superconducting multiterminal devices such as nanocryotrons, yTron, and tunable weak links.

cond-mat.supr-con↗

arXiv2026

Effect of pulse duration on current-induced selective oxygen migration in high-Tc superconductors

High current densities can induce the directional diffusion of atoms in metallic films. In YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO), this electromigration process selectively acts on oxygen atoms lying in the Cu-O chains, permitting to vary the oxygen concentration in a targeted spot of high current density. This approach has proven successful in mapping the phase diagram of the material as a function of carrier concentration or as a way to manufacture memristive devices owing to its reversibility under small bipolar excitations. Thus far, most of the investigations have been limited to pulsed excitation with current/voltage pulses on a millisecond or longer scale, for which thermal effects undeniably influence the process. In the present work, we explore the impact of pulse length $\delta t$ on the onset current of electromigration, $I_{\text{EM}}$, of YBCO bridges, covering the range from 200 ns to 1 ms. As $\delta t$ decreases below $\sim 10~\mu$s, $I_{\text{EM}}$ exhibits a rapid increase. Analytical and numerical estimates of the local temperature show that as pulses shorten, the temperature decreases, making the electromigration process more athermal. These findings are relevant for the operation of memristors and should be taken into account when describing the effects of thermomagnetic instabilities in thin films.

cond-mat.supr-con↗

arXiv2026

Engineering Magnetic Anisotropy in Permalloy Films via Atomic Force Nanolithography

Atomic force nanolithography provides a precise method for sculpting magnetic thin films, enabling controlled engineering of magnetic anisotropy in soft ferromagnets at the microscale. We demonstrate that nanoscale groove arrays patterned into permalloy (Ni80Fe20) films induce a robust in-plane uniaxial anisotropy, with the easy axis aligned along the groove direction. The anisotropy field is shown to increase with decreasing groove period and increasing engraving depth, offering continuous tunability of magnetic hardness within a single fabrication step. Artificially engraved microstructures further allow domain configurations and domain-wall trajectories to be directed along predefined pathways, exemplified by the creation of a chessboard-like magnetic landscape. Owing to its adaptability to diverse ferromagnetic materials and arbitrary corrugation geometries, this approach provides a versatile platform for tailoring in-plane magnetic anisotropy. Concrete applications are demonstrated in the design of magnonic elements and anisotropic magnetoresistance sensors.

cond-mat.mtrl-sci↗