Nanoscale Imaging Reveals Ordered Patterns Within Superconducting Materials at 71 K

Scientists have developed a new method for quantitatively imaging Abrikosov vortices, fundamental to understanding dissipation and flux pinning within superconducting materials. Clemens Schäfermeier, Ankit Sharma and Christopher Kelvin von Grundherr from attocube systems GmbH, in collaboration with Andrea Morales, Jan Rhensius and Gabriel Puebla-Hellmann from QZabre AG, and working with colleagues at attocube systems GmbH, demonstrate cryogenic scanning nitrogen-vacancy magnetometry to visualise these vortices in BSCCO-2212 and YBCO samples under controlled conditions.

This research, utilising continuous-wave optically detected magnetic resonance, provides quantitative magnetic-field maps with nanoscale resolution, revealing a well-ordered vortex lattice in BSCCO-2212 and a more disordered arrangement in YBCO, all while maintaining agreement between measured vortex density and applied magnetic field. The ability to achieve such remarkable magnetic resolution in just 2 to 4 hours establishes this technique as a powerful tool for real-space studies of vortex behaviour in high-temperature superconductors. This work centres on imaging Abrikosov vortices, quantised magnetic flux tubes that form within type-II superconductors when exposed to magnetic fields, using cryogenic scanning nitrogen vacancy magnetometry (NVM). The technique allows for quantitative mapping of these vortices with unprecedented spatial resolution, revealing details of their arrangement and density. Understanding vortex behaviour is crucial for optimising superconducting materials for applications ranging from high-field magnets to quantum technologies. The study successfully imaged these vortices in two widely studied cuprate superconductors, BSCCO-2212 and YBCO, under controlled, field-cooled conditions. In BSCCO-2212 at 71 K, a highly ordered triangular vortex lattice was resolved, confirming its symmetry and spacing through two-dimensional Fourier analysis and consistency with the fundamental principle of flux quantization. YBCO thin films, examined at 3 K, displayed a more disordered vortex arrangement, indicative of stronger pinning forces that prevent the vortices from moving freely. Crucially, the measured vortex density in both materials corresponded quantitatively with the applied magnetic field, validating the accuracy of the NVM technique. This achievement stems from integrating a commercial scanning NVM system into a closed-cycle cryostat, enabling low-vibration, long-duration scans without the need for complex sample preparation or custom setups. The system employs a diamond probe containing a nitrogen vacancy (NV) centre, a defect in the diamond lattice that acts as a highly sensitive magnetic field sensor, and an integrated microwave line for efficient operation at cryogenic temperatures. The resulting magnetic resolution is remarkable, with full field maps acquired in 2 to 4 hours, establishing cryogenic scanning NVM as a powerful tool for real-space studies of high-temperature superconductivity. This method offers a direct, absolute measurement of the magnetic field, eliminating the need for calibration factors common in other techniques. Vortex lattice structures and nanoscale magnetic field mapping in high-temperature superconductors Measurements performed on BSCCO-2212 at 71 K revealed a well-ordered triangular vortex lattice, demonstrating clear evidence of flux quantization. Two-dimensional Fourier analysis confirmed the symmetry and spacing of this lattice, aligning with theoretical predictions for Abrikosov vortices. The observed lattice spacing directly corresponds to the expected arrangement of quantized flux lines within the superconductor. YBCO thin films, imaged at 3 K, exhibited a more disordered vortex arrangement, indicative of stronger flux pinning within the material. Quantitative agreement between the measured vortex density and the applied magnetic field was maintained, validating the accuracy of the scanning nitrogen vacancy magnetometry technique. The research successfully resolved individual vortices with nanoscale spatial resolution, achieving acquisition times of between 2 and 4 hours. This rapid data collection, combined with the remarkable magnetic resolution, establishes cryogenic scanning NVM as a robust quantitative tool for real-space studies of high-temperature superconductors. The observed vortex density in YBCO consistently matched the applied magnetic field, confirming the direct relationship between these two parameters and demonstrating the technique’s ability to accurately quantify magnetic flux penetration. The ability to discern a triangular lattice in BSCCO-2212 and a more disordered arrangement in YBCO highlights the sensitivity of the method to variations in material properties and pinning mechanisms. This work provides quantitative magnetic-field maps with a resolution previously unattainable without complex sample preparation or limitations in sensor performance. Cryogenic nitrogen-vacancy magnetometry with on-chip microwave enhanced resolution A commercial cryogenic scanning nitrogen vacancy magnetometry (NVM) system, integrated into an ultra-low vibration attoDRY2200 cryostat, underpinned the work. This setup combines confocal and wide-field optics with a tuning-fork atomic force microscope (AFM) to precisely control the distance between the tip and the sample surface. Crucially, the system employs QZabre diamond tips, each featuring an on-chip microwave line, eliminating the need for microwave patterning directly on the superconducting materials and enabling low-drift, multi-hour scans. This innovation streamlines sample preparation and expands the scope of long-duration experiments. Continuous-wave optically detected magnetic resonance (cw-ODMR) was used as the primary measurement technique. The NVM leverages the Zeeman effect, establishing a direct and quantitative relationship between the nitrogen-vacancy (NV) electron spin resonance frequency and the local magnetic field. This allows for absolute magnetic field determination without requiring sensor-specific calibration factors, a significant advantage for quantitative vortex imaging. The research was conducted between 1.8 K and 300 K, achieving sensitivities of μT/√Hz, facilitating detailed analysis across a broad temperature range. Samples of BSCCO-2212 and YBCO thin films were field-cooled under controlled conditions prior to imaging. The resulting magnetic-field maps, acquired with nanoscale spatial resolution, were then subjected to two-dimensional Fourier analysis. This mathematical technique transforms the real-space field map into reciprocal space, revealing the underlying periodicity of the Abrikosov vortex lattice. The magnitude of the first-order Bragg peaks in the Fourier transform directly correlates to the lattice spacing, providing a quantitative measure of vortex arrangement and density. The sharpness and six-fold symmetry of these peaks were assessed to determine the degree of lattice order.

The Bigger Picture Scientists have long sought to directly visualise the subtle dance of magnetic vortices within high-temperature superconductors, and a new advance in cryogenic scanning nitrogen-vacancy magnetometry brings that goal significantly closer. For decades, understanding and controlling these vortices, tiny whirlpools of magnetic flux, has been the key to unlocking the full potential of these materials, but their nanoscale nature and the extreme conditions required for observation have presented formidable challenges. Previous techniques, while insightful, often lacked the necessary resolution or quantitative precision to fully map these complex arrangements. This work doesn’t merely offer another image of vortices; it delivers a calibrated, quantitative map of their distribution, revealing the ordered triangular lattice in one material and the stronger pinning effects in another. The ability to reliably measure vortex density with nanoscale spatial resolution, achieved within a practical timeframe, is a substantial step forward. It moves beyond qualitative observation towards a level of detail that allows for direct comparison with theoretical models and facilitates the design of materials with enhanced superconducting properties. However, limitations remain. While the technique excels at imaging the vortex structure, it is currently limited to relatively small areas and requires cryogenic temperatures. Extending the imaging area and potentially achieving room-temperature operation would dramatically broaden its applicability. Future work might focus on combining this technique with other characterisation methods, such as transport measurements, to correlate vortex behaviour with macroscopic properties. The research revealed a well-ordered lattice in BSCCO-2212, while YBCO displayed a more disordered arrangement. This demonstrates the sensitivity of the method to variations in material properties and pinning mechanisms. Ultimately, the goal is not just to see these vortices, but to engineer materials where they behave in a way that maximises current flow and minimises energy loss, bringing us closer to practical superconducting technologies. 👉 More information🗞 Quantitative imaging of Abrikosov vortices by scanning quantum magnetometry🧠 ArXiv: https://arxiv.org/abs/2602.13060 Tags: