Irradiation of a material with ions can cause various defects that can lead to structural phase transitions and the modification of the material's properties. Here we study the irradiation of the epitaxyally grown thin films of the high-temperature superconductor YBa_2Cu_3O_7 with 30 keV He^+ ions which leads to the expansion of the crystal lattice, decrease of the critical temperature T_c and eventually transition to an insulator. Fabrication of such insulating regions with a focused He-Ion beam with a spot size of ∼ 10 nm is a powerful technique for fabrication of superconducting nano-devices. Using low-temperature resistivity measurements, diffraction with a nanofocused X-ray beam and atomic force microscopy, we investigated how the structure and the electric transport properties of YBa_2Cu_3O_7 depend on the irradiation dose in a range 10–100 ions/nm^2 and on the lateral size of the irradiated area in a range 30–5000 nm.

Recent results with shunted YBa2Cu3O7-x Josephson junctions (JJs) fabricated using direct-writing by helium-focused ion beam (He-FIB) demonstrate that this technology is useful to achieve a YBa2Cu3O7-x voltage standard. By adding a shunt resistor via a subsequent lift-off step, the ${{{R}}}_{\text{n}}$ value and thereby the spread of the JJs can be reduced. These results were achieved with one large shunt across multiple JJs. This study presents different designs of shunt resistors, which allow measuring the JJs individually. The different shunt resistor designs are described and evaluated by comparing measurement results without and with the shunt resistor. These show the desired effect of controlling ${{R}}_{\text{n}}$, but also a change in ${{I}}_{\text{c}}$ is visible. The spread in parameters is investigated both without and with shunt resistors. Shapiro steps at gigahertz frequencies are presented for single JJs. The study concludes with a comparative measurement between a YBa2Cu3O7-x He-FIB JJ and a Josephson Arbitrary Waveform Synthesizer from PTB Braunschweig, showing a deviation of 0.05${\%}$ and thus demonstrating its potential applicability.

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.

This article presents a compact, single-ended high-temperature superconducting (HTS) helium-focused ion beam (He-FIB) Josephson junction (JJ) mixer. The planar circuit is fabricated from a thin film layer of YBa2Cu3O7-x deposited on a 10 mm & times; 10 mm Lanthanum Strontium Aluminium Tantalate (LSAT) substrate. A comprehensive six-step microstrip design methodology is outlined, detailing the JJ's physical geometries, high frequency and DC grounding, impedance matching, and filtering networks. The complete microstrip topology is designed to achieve an approximate radio frequency (RF) input passband between 9.9 to 10.6 GHz with high out-of-band isolation, a single local oscillator resonance at 11.54GHz and an intermediate frequency lowpass cut-off at 2.3GHz. The proposed RF impedance matching network is uniquely designed to mitigate the significant performance limitation associated with normal resistances (R-n) scatter observed in HTS JJs. By implementing the proposed design methodology, a stable percentage bandwidth and S-11 <= -10dB is maintained between R-n= 5 to 10 Omega, which coincides with the fabrication variance for He-FIB JJs. The HTS mixer is manufactured, and its DC and high-frequency behaviors are characterized at 6, 10, 20, 30, and 40K. The measured Rn is 9.77 Omega, which significantly deviated from the predicted value of 5 Omega, emphasizing the importance of the adaptability and versatility of the implemented impedance matching network. Exposed to the lowest measured temperature, the HTS mixer exhibited a maximum conversion gain of -4.93dB, which demonstrates the potential capabilities in He-FIB induced barrier JJs on LSAT substrates as frequency mixers.

Helium focused ion beam irradiation enables the fabrication of tunnel field-effect transistors based on two-dimensional electron systems (2DESs) at an oxide interface.High resolution scanning transmission electron microscopy and strain mapping reveal localized lattice deformation confined to the irradiated regions, which act as nanoscale potential barriers. The barrier profile can be continuously tuned by electrostatic backgating at low temperature without degrading the electronic properties of the 2DES electrodes. Transport measurements demonstrate controlled access to thermionic emission, direct tunneling, and Fowler-Nordheim tunneling within a single device architecture. These results establish He FIB irradiation as a powerful tool for nanoscale functional engineering of complex-oxide interfaces and provide a platform for exploring gate-tunable quantum tunneling phenomena.

Fabrication of YBa2Cu3O7-x Josephson junctions (JJs) using a direct-write helium-focused helium ion beam (He-FIB) technique has great potential for various applications due to tunable JJ parameters and arbitrary positioning. This technique allows placing multiple JJs in series to create JJ arrays. They could be used as a voltage standard that is operated at higher temperatures and driving frequencies than the currently used niobium-based JJ arrays. Small YBa2Cu3O7-x He-FIB JJ arrays with superposed Shapiro steps for up to three JJs have already been demonstrated. The number of JJs in the array was limited by the parameter spread of the individual JJs. This study presents WRspice simulations of JJ arrays, which indicate that the normal state resistance $R$(n) is the most crucial parameter to achieve flat Shapiro steps in JJ arrays. The idea of adding a shunt resistor to the JJ array to deal with the spread in $R$(n) values is investigated. A new design for GHz frequencies is presented, and the fabrication process is described. The properties of the shunt resistor are evaluated by van der Pauw measurements. Comparison of measurements with and without shunt resistor shows the desired effect of changing the total resistance of the JJ array while maintaining the critical current value. Finally, measurements of JJ arrays demonstrating superposed Shapiro steps at 20 k at GHz frequencies are presented.

The development of a fabrication process for Josephson junctions (JJs) using a direct-write helium-focused ion beam (He-FIB) technique provides the opportunity to control parameters such as the critical current $I$ c and normal-state resistance $R$ n of individual JJs in YBa 2 Cu 3 O 7-x JJ arrays. Such arrays could be used as a voltage calibration standard that is operated at higher temperatures and higher driving frequencies than the currently used niobium JJ arrays. This study presents the fabrication process of 79 YBa 2 Cu 3 O 7-x JJs in a meander array design using a direct writing He-FIB process with the same irradiation dose for all JJs. In this design, each of the JJs can be measured individually, and adjacent JJs that exhibit similar and suitable parameters for a voltage standard array can be measured in series. The scattering of the JJ parameters was investigated at 5 K and resulted in a spread in $I$ c of about 60% and in $R$ n of 25%. However, a couple of subarrays with a spread lower than 10% could be found. In addition, these JJ subarrays were irradiated with high-frequency radiation in the GHz and THz range at a temperature of 20 K and synchronization of up to three JJs was observed in both frequency ranges.

Fabrication of YBa2Cu3O7-x Josephson junctions (JJs) using a direct-write helium-focused ion beam (He-FIB) technique has great potential for various applications due to tunable JJ parameters and arbitrary positioning. This technique allows placing multiple JJs in series to create JJ arrays. They could be used as a voltage standard that is operated at higher temperatures and driving frequencies than the currently used niobium-based JJ arrays. Small YBa2Cu3O7-x He-FIB JJ arrays with superposed Shapiro steps for up to three JJs have already been demonstrated. The number of JJs in the array was limited by the parameter spread of the individual JJs. This study presents WRspice simulations of JJ arrays, which indicate that the normal state resistance $R$nis the most crucial parameter to achieve flat Shapiro steps in JJ arrays. The idea of adding a shunt resistor to the JJ array to deal with the spread in $R$nvalues is investigated. A new design for GHz frequencies is presented, and the fabrication process is described. The properties of the shunt resistor are evaluated by van der Pauw measurements. Comparison of measurements with and without shunt resistor show the desired effect of changing the total resistance of the JJ array while maintaining the critical current value. Finally, measurements of JJ arrays demonstrating superposed Shapiro steps at 20K at GHz frequencies are presented.

Using a focused He+ beam for nanopatterning and writing of Josephson barriers, we fabricated specially shaped Josephson junctions of in-line geometry in YBa2Cu3O7 thin film microbridges with an asymmetry ratio of critical currents of opposite polarities of approximately 7 at the optimum magnetic field. Those Josephson diodes were subsequently used as ratchets to rectify an applied alternating current into a dc voltage. We also demonstrate the operation of such a ratchet in the loaded regime, where it produces a nonzero dc output power and yields a thermodynamic efficiency of up to 75%. The ratchet shows record figures of merit: an output dc voltage of up to 212 mu V and an output power of up to 0.2 nW. The device has an essential area of approximately 1 mu m2. For rectification of quasistatic Gaussian noise, the figures of merit are more modest; however, the efficiency can be as high as for the deterministic ac drives within some regimes. Since the device is based on YBa2Cu3O7, it can operate at temperatures up to approximately 40 K, where more noise is available for rectification.

By focused 30 keV He ion beam irradiation, epitaxially grown YBa_2Cu_3O_7 (YBCO) thin films can be driven from the superconducting to the insulating state with increasing irradiation dose. A properly chosen dose suppresses superconductivity down to 4 K, while crystallinity is still preserved. With this approach we create areas of normal-conducting YBCO that can be used to define resistively shunted constriction-type Josephson junctions (cJJs) on the nanometer scale. We also demonstrate that the fabricated cJJs can be incorporated in direct current superconducting quantum interference devices and can be used as detector junctions in THz antennas.

Using a $30\,\mathrm{keV}$ focused He ion beam (He-FIB) with a wide range of irradiation doses $D=100$ to $1000\,\mathrm{ions/nm}$ we fabricated Josephson and resistive barriers within microbridges of epitaxially grown single crystalline YBCO thin films and investigated the change of their electric transport properties with time. One set of samples (#1A) was simply stored at room temperature under nitrogen atmosphere. A second set (#2D) was post-annealed at $90^\circ\,\mathrm{C}$ using high oxygen pressures and a third set (#2E) at low oxygen pressures. We found that for #1A the critical current density $j_c$ at $4.2\,\mathrm{K}$ changes as $j_c\propto\exp(-\sqrt{t/\tau})$ with time $t$, where the relaxation times $\tau$ increases exponentially with $D$, which can be described within a limited diffusion based model. In order to increase the diffusion rate we annealed the junctions from #2D at $90^\circ\,\mathrm{C}$ for $30\,\mathrm{min}$ in oxygen environment. Directly after annealing the critical current density $j_c$ increased, while the normal state resistance $R_n$ decreased. Repeated measurements showed that within a week the junctions relaxed to a quasi-stable state, in which the time scale for junction parameter variations increased to several weeks, making this a feasible option to achieve temporal stability of parameters of He-FIB Josephson junctions in YBCO.

Thin films of the superconductor YBa2Cu3O7−δ (YBCO) were modified by low-energy light-ion irradiation employing collimated or focused He+ beams, and the long-term stability of irradiation-induced defects was investigated. For films irradiated with collimated beams, the resistance was measured in situ during and after irradiation and analyzed using a phenomenological model. The formation and stability of irradiation-induced defects are highly influenced by temperature. Thermal annealing experiments conducted in an Ar atmosphere at various temperatures demonstrated a decrease in resistivity and allowed us to determine diffusion coefficients and the activation energy ΔE=(0.31±0.03) eV for diffusive oxygen rearrangement within the YBCO unit cell basal plane. Additionally, thin YBCO films, nanostructured by focused He+-beam irradiation into vortex pinning arrays, displayed significant commensurability effects in magnetic fields. Despite the strong modulation of defect densities in these pinning arrays, oxygen diffusion during room-temperature annealing over almost six years did not compromise the signatures of vortex matching, which remained precisely at their magnetic fields predicted by the pattern geometry. Moreover, the critical current increased substantially within the entire magnetic field range after long-term storage in dry air. These findings underscore the potential of ion irradiation in tailoring the superconducting properties of thin YBCO films.

Using a focused He^+ beam for nanopatterning and writing of Josephson barriers we fabricated specially shaped Josephson junctions of in-line geometry in YBa_2Cu_3O_7 thin film microbridges with an asymmetry ratio of critical currents of opposite polarities (non-reciprocity ratio) ≈ 7 at optimum magnetic field. Those Josephson diodes were subsequently used as ratchets to rectify an applied ac current into a dc voltage. We also demonstrate the operation of such a ratchet in the loaded regime, where it produces a nonzero dc output power and yields a thermodynamic efficiency of up to 75 %. The ratchet shows record figures of merit: an output dc voltage of up to 212 μV and an output power of up to 0.2 nW. The device has an essential area ≈ 1 μm^2. For rectification of quasistatic Gaussian noise, the figures of merit are more modest, however the efficiency can be as high as for the deterministic ac drives within some regimes. Since the device is based on YBa_2Cu_3O_7, it can operate at temperatures up to ∼40 K, where more noise is available for rectification.

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 YBa2Cu3O7-s 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 a matching field of 6 T visible in a huge temperature range from the critical temperature Tc 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 Tc, where superconductivity is robust.

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 YBa2Cu3O7−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 a matching field of 6 T visible in a huge temperature range from the critical temperature Tc 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 Tc, where superconductivity is robust. Published by the American Physical Society 2024

We present a theoretical investigation of the stochastic dynamics of a damped particle in a tilted periodic potential with a double well per period. By applying the matrix continued fraction technique to the Fokker-Planck equation in conjunction with the full counting statistics and master equation approaches, we determine the rates of specific processes contributing to the system's overall dynamics. At low temperatures, the system can exhibit one running state and two distinct locked metastable states. We focus primarily on two aspects: the dynamics of positional jumps, which are rare thermally induced particle jumps over potential maxima, and their impact on the overall velocity noise; and the retrapping process, involving the transition from the running to the locked metastable states. We demonstrate the existence of fractional (in units of 2 pi) positional slips that differ qualitatively from conventional 2 pi jumps observed in single-well systems. Fractional positional slips significantly influence the system dynamics even in regimes dominated by dichotomous-like switching between running and locked states. Furthermore, we introduce a simple master equation approach that proves effective in analyzing various stages of the retrapping process. Interestingly, our analysis shows that even for a system featuring a well-developed double-well periodic potential, there exists a broad parameter range where the stochastic dynamics can be accurately described by an effective single-well periodic model. The techniques introduced here allow for valuable insights into the complex behavior of the system, offering avenues for understanding and controlling its steady-state and transient dynamics, which go beyond or can be complementary to direct stochastic simulations.

Josephson junctions with customizable parameters, including critical current Ic and normal state resistance Rn, hold great promise across a wide range of applications. Notably, hightemperature superconductors like YBa 2 Cu 3 O 7-x have been interesting since their discovery due to their simplified cooling requirements. YBa 2 Cu 3 O 7-x Josephson junctions can operate within the terahertz (THz) frequency range, rendering them highly suitable for various applications. To maximize their suitability at these high frequencies, it is imperative to precisely determine their THz parameters. Helium focused ion beam (He-FIB) technology is a very promising fabrication method for customizable Josephson junctions. It allows precise control of the He-FIB dose during the fabrication of Josephson junctions and facilitates the finetuning of Ic and Rn. This study presents the fabrication process of YBa 2 Cu 3 O 7-x Josephson junctions using He-FIB irradiation and explores the variations of parameters with dose, evaluating their suitability within the THz range. Also, the scattering of parameters of He-FIB Josephson junctions fabricated with the same He-FIB dose is investigated. Additionally, we examine the high-frequency properties of such junctions and scrutinize the associated Shapiro steps within the THz frequency spectrum. We observe an exponential relationship between Ic and the HeFIB dose. Moreover, Shapiro steps emerge under the influence of radiation spanning from 40 GHz to as high as 1.4 THz.

The competition between intrinsic disorder in superconducting YBa2Cu3O7−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 (Tg) vs. applied magnetic field (Ba) 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.

We have proposed a new design of the Josephson traveling-wave parametric amplifier (JTWPA) capable of providing much higher spurious-free dynamic range (SFDR). For this purpose, we substitute dc SQUIDs for bi-SQUIDs in the used artificial signal transmission line driven by external travelling-wave magnetic flux. The increase of SFDR follows from the increased linearity domain of the phase-current relation in bi-SQUID as compared to dc SQUID. Optimal parameters for bi-SQUIDs have been determined. The first version of JTWPA was modeled to be fabricated using niobium process.