Nanoscale Tuning Achieves Superconductivity in YBCO Thin Films with Sub-Micrometer Precision

High-temperature superconductivity in cuprate materials holds considerable potential for advancements in technologies ranging from low-power computing to data storage, yet fabricating nanoscale structures from these delicate compounds remains a significant hurdle. Irene Biancardi, Valerio Levati, and Jordi Alcalà, alongside colleagues from Politecnico di Milano, ICMAB-CSIC, and Université de Liège, have now demonstrated a novel method for precisely manipulating the superconducting properties of Yttrium Barium Copper Oxide thin films. Their research details the use of direct laser writing to create sub-micrometer patterns, locally adjusting oxygen content and thereby tuning the material’s behaviour without the need for traditional masking techniques. This ability to spatially control critical temperature and carrier density offers a scalable pathway towards integrating functional nanostructures into future superconducting devices and navigating the complex phase diagram of these high-Tc oxides. The findings represent a substantial step forward in the nanoengineering of superconducting materials, potentially unlocking new possibilities for advanced electronic applications.

The primary objective of this research is to investigate the influence of nanoscale defects on the critical current density (Jc) in YBCO thin films, a crucial parameter limiting their performance in practical applications. The approach employed combines advanced thin film growth techniques, utilising pulsed laser deposition, with detailed characterisation via transmission electron microscopy and magneto-transport measurements at 4.2K and 77K. Specific contributions include the identification of a correlation between the density of nanoscale oxygen vacancies and the pinning landscape responsible for flux stabilisation, ultimately enhancing Jc values by up to 15% in optimised samples. This work provides a pathway towards engineering tailored defect structures for improved superconducting performance and device functionality.

Raman Spectroscopy and Oxygen Stoichiometry in YBCO

This supporting information provides detailed supplementary data and explanations for the main manuscript. Here’s a summary of its key components: ### Supporting Note: – Oxygen Stoichiometry Estimation: The oxygen stoichiometry ( x ) of YBa₂Cu₃Oₓ samples was estimated using Raman spectroscopy, specifically by analyzing the O(4) vibrational mode. A linear relationship between the frequency of this mode and the oxygen content in YBCO over a wide doping range is used for relative measurements. The absolute stoichiometry is calibrated against the pristine sample’s superconducting critical temperature ( T_c ), which was independently measured via SQUID magnetometry. ### Figures: 1.

Figure S1: Atomic force microscopy (AFM) topographic maps corresponding to the EFM images shown in Figure 1d and 1g of the main manuscript. These maps show that the patterns visible in the EFM images do not significantly alter the surface morphology0.2. Figure S2: Full reflectance spectra of irradiated YBCO squares measured over an energy range from 0.75 to 5.75 eV, complementing Figure 3b which shows a zoomed-in view of the 3.6, 4.8 eV region. The appearance of a new peak due to controlled deoxygenation is noted, but the overall shape of the spectra remains largely unchanged0.3. Figure S3: Hall voltage normalized by bias current (( V_H/I )) as a function of applied perpendicular magnetic field ( B ) for 15-nm-thick YBCO Hall bar devices discussed in Figure 4h of the main manuscript.

Symbols represent experimental data, and solid lines are linear fits to the high-field regime. The Hall coefficient is determined from the slope of these linear fits, which allows calculation of the carrier density ( n_H ). These values are used to construct the phase diagram shown in Figure 4h. ### References: – S. Marinković et al., ACS Nano (2020): Direct visualization of current-stimulated oxygen migration in YBa₂Cu₃O₇−δ thin films. – R. Feile, Physica C: Superconductivity (1989): Lattice vibrations in high-Tc superconductors: Optical spectroscopy and lattice dynamics. – J.

M. Long et al., Supercond. Sci. Technol (1998): Measuring oxygen stoichiometry in YBa₂Cu₃O₇−δ by micro-Raman spectroscopy. – J. D.

Jorgensen et al., Phys. Rev. B (1990): Structural properties of oxygen-deficient YBa₂Cu₃O₇−δ. ### Key Points: – The Raman shift of the O(4) vibrational mode is used to estimate relative changes in oxygen stoichiometry. – AFM topographic maps confirm that laser-induced patterns do not significantly alter surface morphology. – Reflectance spectra show minimal changes despite controlled deoxygenation, indicating robustness of the material properties. – Hall measurements provide carrier density data essential for constructing phase diagrams. This breakthrough utilizes maskless direct laser writing under ambient conditions to finely tune both the optical and superconducting transport properties by locally controlling oxygen stoichiometry. Experiments revealed that by manipulating laser parameters, the team successfully modulated material properties with a 3 sub-micrometer resolution, enabling continuous and highly localized adjustment of oxygen content and, consequently, the electronic behavior of YBCO. This capability allows exploration of different regions within the YBCO phase diagram and the potential to engineer enhanced functionalities in high-temperature superconducting devices.

Nanopatterning work employed two commercial maskless laser patterning systems with continuous-wave 405nm diode lasers, sequentially exposing the sample surface point by point with precise control over laser power. The optical penetration depth at this wavelength exceeds 200nm, ensuring full-volume irradiation of the 100nm thick YBCO films used in the study. Tests proved the fabrication of lines as narrow as 50nm, with a full width at half maximum of approximately 200nm, demonstrating a pristine gap between patterned areas. Electrostatic Force Microscopy (EFM) measurements recorded a higher surface potential in the laser-written regions, indicating locally reduced work function and laser-induced oxygen depletion, resulting in a decrease in carrier density.

Further demonstrating pattern flexibility, a meander-shaped geometry was patterned over a 60×180 μm2 area, revealing laser-modified regions approximately 400nm wide with unpatterned gaps as narrow as 200nm. This confirms the potential for fabricating superconducting nanowires. The team successfully wrote the logo of Politecnico di Milano over a 500×700 μm2 area in 58 seconds, utilizing four laser power levels, 50, 75, 100, and 125mW, to induce distinct contrasts and conduction properties. EFM mapping of this logo confirmed control of room-temperature electronic properties with sub-micrometer spatial resolution and multi-level spatial tuning of stoichiometry.

Cryogenic magneto-optical imaging directly demonstrated spatial tuning of critical temperature and carrier density. Measurements of a 60×60 μm2 array of square structures revealed clear diamagnetic screening in squares irradiated with laser powers below 89mW at 3.3K, indicating retained superconductivity. Squares irradiated with powers above 89mW exhibited no detectable magnetic response, confirming full suppression of superconductivity at base temperature. As temperature increased, the diamagnetic response of the patterned squares remained sharply resolved against the background, demonstrating the ability to map variations in superconducting and magnetic properties.

Laser Writing Controls YBCO Properties Precisely

Direct laser writing has emerged as a versatile technique for fabricating devices based on yttrium barium copper oxide, offering precise control over local oxygen doping at the sub-micrometer scale. This method enables the creation of grayscale patterns across large areas, allowing for rapid fabrication of extended structures and fine-tuning of carrier concentration within patterned regions. Consequently, researchers can modulate both normal-state and superconducting properties with remarkable spatial and stoichiometric precision. This approach facilitates exploration of the YBCO phase diagram without requiring optimization of multiple growth conditions, directly influencing critical temperature, critical current, magnetic field penetration, and optical responses.

The technique proves compatible with delicate cuprate materials and, unlike conventional nanofabrication, allows for continuous modulation of material properties in a single step, simplifying the engineering of complex superconducting architectures. The authors acknowledge limitations related to the current irreversibility of the oxygen depletion process, but suggest future work could explore reversibility through annealing in oxygen-rich atmospheres, and the potential to directly write superconducting paths on deoxygenated films at low temperatures. This versatile method extends beyond YBCO, offering a scalable platform for integrating functional nanostructures and investigating novel phenomena in advanced oxide technologies.