Josephson Junctions and SQUIDs Created by Focused Helium-Ion-Beam Irradiation of Y Ba 2 Cu 3 O 7

Authors: B. Müller, M. Karrer, F. Limberger, M. Becker, B. Schröppel, C.J. Burkhardt, R. Kleiner, E. Goldobin, and D. Koelle

Physical Review Applied volume 11, 044082 (2019)

Abstract: By scanning with a $30$–$\mathrm{keV}$ focused $\mathrm{He}$ ion beam ($\mathrm{He}$-FIB) across ${Y\mathrm{Ba}}_2{\mathrm{Cu}}_3{O}_7$ (YBCO) thin-film microbridges, we create Josephson barriers with critical current density $j_c$ adjustable by irradiation dose $D$. The dependence $j_c\left(D\right)$ yields an exponential decay. At $4.2K$, a transition from flux-flow to Josephson behavior occurs when $j_c$ decreases below approximately $2\mathrm{MA}/c{m}^2$. The Josephson junctions exhibit current-voltage characteristics (IVCs) that are well described by the resistively and capacitively shunted junction model, without excess current for characteristic voltages $V_c\lesssim 1\mathrm{mV}$. Devices on $\mathrm{Mg}O$ and LSAT substrates show nonhysteretic IVCs, while devices on ${\mathrm{Sr}\mathrm{Ti}O}_3$ show a small hysteresis. For all junctions, an approximate scaling $V_c\propto j_c^{1/2}$ is found. $\mathrm{He}$-FIB irradiation with a high dose produces barriers with $j_c=0$ and high resistances of $10k\Omega$ to $1G\Omega$. This provides the possibility to write highly resistive walls or areas into YBCO using a He-FIB. Transmission electron microscopy reveals an amorphous phase within the walls, whereas for lower doses the YBCO stays crystalline. We have also “drawn” superconducting quantum-interference devices (SQUIDs) by using a $\mathrm{He}$-FIB for the definition of the SQUID hole and the junctions. The SQUIDs show high performance, with flux noise $<500n{\Phi }_0/H{z}^{1/2}$ in the thermal white-noise limit for a device with $19\mathrm{pH}$ inductance.

DOI: 10.1103/PhysRevApplied.11.044082