arXiv subjects

Katja Wurster

Publications and source records attributed to Katja Wurster.

5 recordsLinked to original sources

arXiv2026

Tailoring the properties of YBa$_{2}$Cu$_{3}$O$_{7-δ}$ thin films by 30 keV He$^+$ irradiation: An enabling route to superconducting device nanopatterning

Focused helium ion beam (He-FIB) irradiation with 30 keV ions is a key tool for nanoscale patterning and defect engineering in high transition temperature (Tc) cuprate superconducting devices, yet its usable fluence window is constrained by the competing requirements of reliable superconductivity suppression and minimal structural degradation. In this work, we provide a comprehensive dataset on the effects of large-area 30 keV He+ ion exposure on the electric transport and superconducting properties of epitaxial YBa2Cu3O7 (YBCO) thin films. X-ray diffraction shows a fluence-driven loss of crystalline order accompanied by an out-of-plane lattice expansion and an orthorhombic-to-tetragonal transition, culminating at predominant amorphization at the highest fluence of 1 x 10^16 cm^-2. Raman spectra exhibit increasing disorder while lacking signatures of oxygen depletion, indicating that irradiation mainly generates oxygen-related Frenkel defects rather than changing the carrier concentration. Consistently, with increasing fluence, the normal-state resistivity ρ_N(T) at temperature T above Tc increases strongly, while d ρ_N/d T remains nearly unchanged at moderate fluence. The suppression of Tc is accurately described by Abrikosov-Gor'kov pair breaking and reaches complete quenching of superconductivity at 4.5 x 10^15 cm^-2. The anisotropic upper critical fields decrease approximately exponentially with increasing fluence, the vortex activation energy is reduced, and the anisotropy drops, in contrast to oxygen-depleted YBCO. Hall-angle analysis confirms a nearly constant carrier density but a systematic increase in defect scattering and reduced mobility, consistent with a crossover toward the dirty limit at high fluence. These results establish quantitative fluence thresholds and a practical operational window for He-FIB nanopatterning of YBCO quantum circuits.

cond-mat.supr-con↗

arXiv2024

Vortex matching at 6 T in YBa$_2$Cu$_3$O$_{7-δ}$ thin films by imprinting a 20 nm-periodic pinning array with a focused helium ion beam

Controlled engineering of vortex pinning sites in copper-oxide superconductors is a critical issue in manufacturing devices based on magnetic flux quanta. To address this, we employed a focused He-ion beam (He-FIB) to irradiate thin YBa$_2$Cu$_3$O$_{7-δ}$ films and create ultradense hexagonal arrays of defects with lattice spacings as small as 20 nm. Critical current and magnetoresistance measurements demonstrate efficient pinning by an unprecedentedly high matching field of 6 T visible in a huge temperature range from the critical temperature $T_c$ down to 2 K. These results show that He-FIB irradiation provides excellent opportunities for the development and application of superconducting fluxonic devices based on Abrikosov vortices. In particular, our findings suggest that such devices can operate at temperatures far below $T_c$, where superconductivity is robust.

cond-mat.supr-con↗

arXiv2024

Vector-substrate-based Josephson junctions

We present a way to We present a way to fabricate bicrystal Josephson junctions of high-Tc cuprate superconductors that does not require bulk bicrystalline substrates. Based on vector substrate technology, this novel approach makes use of a few tens-of-nanometers-thick bicrystalline membranes transferred onto conventional substrates.We demonstrate 24° YBa2Cu3O7-x Josephson junctions fabricated on sapphire single crystals by utilizing 10-nm-thick bicrystalline membranes of SrTiO3. This technique allows one to manufacture bicrystalline Josephson junctions of high-Tc superconductors on a large variety of bulk substrate materials, providing novel degrees of freedom in designing the junctions and their electronic properties. It furthermore offers the capability to replace the fabrication of bulk bicrystalline substrates with thin-film growth methods

cond-mat.supr-con↗

arXiv2023

Angle-dependent Magnetoresistance of an Ordered Bose Glass of Vortices in YBa$_{2}$Cu$_{3}$O$_{7-δ}$ Thin Films with a Periodic Pinning~Lattice

The competition between intrinsic disorder in superconducting YBa$_{2}$Cu$_{3}$O$_{7-δ}$ (YBCO) thin films and an ultradense triangular lattice of cylindrical pinning centers spaced at 30 nm intervals results in an ordered Bose glass phase of vortices. The samples were created by scanning the focused beam of a helium-ion microscope over the surface of the YBCO thin film to form columns of point defects where superconductivity was locally suppressed. The voltage-current isotherms reveal critical behavior and scale in the vicinity of the second-order glass transition. The latter exhibits a distinct peak in melting temperature ($T_g$) vs. applied magnetic field ($B_a$) at the magnetic commensurability field, along with a sharp rise in the lifetimes of glassy fluctuations. Angle-dependent magnetoresistance measurements in constant-Lorentz-force geometry unveil a strong increase in anisotropy compared to a pristine reference film where the density of vortices matches that of the columnar defects. The pinning is therefore, dominated by the magnetic-field component parallel to the columnar defects, exposing its one-dimensional character. These results support the idea of an ordered Bose glass phase.

cond-mat.supr-con↗

arXiv2022

Ordered Bose Glass of Vortices in Superconducting YBa$_{2}$Cu$_{3}$O$_{7-δ}$ Thin Films with a Periodic Pin Lattice Created by Focused Helium Ion Irradiation

The defect-rich morphology of YBa$_{2}$Cu$_{3}$O$_{7-δ}$ (YBCO) thin films leads to a glass-like arrangement of Abrikosov vortices which causes the resistance to disappear in vanishing current densities. This vortex glass consists of entangled vortex lines and is identified by a characteristic scaling of the voltage-current isotherms. Randomly distributed columnar defects stratify the vortex lines and lead to a Bose glass. Here, we report on the observation of an ordered Bose glass in a YBCO thin film with a hexagonal array of columnar defects with 30 nm spacings. The periodic pinning landscape was engineered by a focused beam of 30 keV He$^+$ ions in a helium-ion microscope.

cond-mat.supr-con↗