YBa2Cu3O7 Josephson Nano Devices Fabricated by Focused Helium Ion Beam Irradiation

Abstract

Superconducting electronics enables quantum-accurate metrology, ultrasensitive magnetometry, and terahertz (THz) devices. The established Nb technologies are constrained by a low operating temperature and a limited high-field/high-frequency performance. In the framework of this dissertation, a fabrication platform for high-transition-temperature superconducting nano-devices based on epitaxially grown YBa_2Cu_3O_7 (YBCO) films patterned by focused helium-ion-beam (He-FIB) irradiation is described. He-FIB irradiation locally displaces oxygen atoms in YBCO and allows to continuously tune the superconducting properties without material removal, enabling direct-write creation of weak links, resistive regions, and insulating barriers with nanometer-scale precision.

This thesis accumulates four publications that together provide a deeper insight into the well-established barrier-type Josephson junction and a spectrum of applications. Single JJs and JJ arrays embedded in antenna structures are presented to realize a THz detector, which could lay the foundation of a high-transition-temperature voltage standard. Furthermore, a superconducting diode with record figures of merit is presented. To broaden the range of possible applications, He-FIB induced YBCO resistors are presented, which allow for the fabrication of nano constriction-type Josephson junctions on the resolution limit of the He-FIB. These ultra-small junctions are investigated in SQUIDs and THz antennas to demonstrate their feasibility.