La3ni2o7-delta Exhibits 80 K Superconductivity and Meissner Effect Confirmed Via Diamond Quantum Sensors

The search for new superconducting materials recently focused attention on nickelates, with reports suggesting superconductivity in lanthanum nickelate, La3Ni2O7-delta, under pressure, though definitive proof remained elusive. Lin Liu, Jianning Guo, Deyuan Hu, and colleagues now present compelling evidence for the Meissner effect, the expulsion of magnetic fields that confirms superconductivity, in a single crystal of this material. Using exquisitely sensitive diamond-based quantum sensors, the team simultaneously measured both zero electrical resistance and the Meissner effect within the same crystal, overcoming limitations of previous high-pressure magnetic measurements. This dual confirmation, coupled with detailed mapping of superconducting regions, strongly supports the claim of high-temperature superconductivity in lanthanum nickelate and offers valuable insights into the material’s complex structural and magnetic behaviour.

Quantum sensing with nitrogen-vacancy (NV) centers in diamond enables detailed characterization of magnetic properties in tiny samples, even those with defects. Recent studies suggest superconductivity in La3Ni2O7- under pressure, demonstrating near-zero electrical resistance around 80 K, though confirming the complete Meissner effect, the expulsion of magnetic fields, has proven challenging due to the material’s subtle superconducting behaviour. This research investigates the magnetic properties of this nickelate compound to better understand its superconducting characteristics, employing NV-center magnetometry, a highly sensitive technique, to map the local magnetic fields within the La3Ni2O7- sample under varying pressure. This approach allows for detailed analysis of magnetic variations and identification of magnetic signatures linked to the superconducting state, providing crucial insights into the origin and nature of superconductivity in this nickelate compound.

Nickelate Superconductivity Confirmed at Transition Temperature

This research provides compelling evidence for superconductivity in a nickelate material, a significant finding because nickelates are considered promising candidates for achieving high-temperature superconductivity, similar to cuprates. Building on previous work, the researchers observed a clear superconducting transition, indicating the material loses electrical resistance at a specific temperature, and characterized the superconducting properties, including the critical temperature and critical magnetic fields. The team utilized electrical resistivity and magnetic measurements to detect the superconducting transition and confirm the superconducting state through the Meissner effect. A key component of this work is the application of diamond nitrogen-vacancy (NV) center magnetometry, an advanced technique that uses NV centers as nanoscale sensors to measure extremely weak magnetic fields, allowing for high-resolution mapping of the magnetic field distribution within the superconducting material.

This work contributes to the ongoing search for new high-temperature superconductors, materials that could revolutionize many technologies if they superconduct closer to room temperature. The study reinforces the idea that nickelates are a viable platform for achieving this goal, and the successful application of NV center magnetometry demonstrates its potential for characterizing superconducting materials with unprecedented spatial resolution. The research is motivated by the success of cuprate superconductors and the structural similarities between cuprates and nickelates. Achieving superconductivity in nickelates has been challenging, and the observed superconducting properties are often more fragile than those in cuprates. The quality and precise chemical composition of the nickelate material are critical for achieving superconductivity, and this research represents a significant step forward in the quest for high-temperature superconductivity, providing valuable insights into the fundamental mechanisms and opening new avenues for materials discovery.

La3Ni2O7- Superconductivity Confirmed by Magnetism and Resistance

This work presents a comprehensive investigation of superconductivity in La3Ni2O7- under high pressure, combining electrical transport measurements with nanoscale magnetic imaging using nitrogen-vacancy (NV) centers in diamond. Researchers successfully observed zero resistance at 72 K under 22 GPa and 65 K under 28 GPa, consistent with previous reports, and crucially, also detected the Meissner effect, confirming the material’s superconducting state. Applying the Ginzburg-Landau equations, the team determined upper critical magnetic fields of 86 T at 22 GPa and 71 T at 28 GPa, quantifying the material’s response to external magnetic forces. To visualize the superconducting regions at the nanoscale, the researchers employed an NV center quantum sensor integrated into a cryogenic system.

By mapping the local magnetic response, they detected diamagnetism by cooling the sample below its critical temperature, revealing spatial variations in the superconducting state. Detailed ODMR spectroscopy revealed a notable increase in magnetic field splitting at 51 K compared to 23 K at a specific point under 28 GPa, demonstrating a clear temperature-dependent magnetic response. Analysis of the local magnetic field showed that the field increased with temperature up to approximately 60 K, consistent with the electrical measurements of the superconducting transition temperature. However, measurements at other points exhibited no temperature-dependent change, indicating sample inhomogeneity. These findings demonstrate that the superconducting properties are not uniform throughout the material, highlighting the need for spatially resolved measurements, and zero-field splitting data confirmed comparable stress levels in both superconducting and non-superconducting regions, suggesting that sample inhomogeneity, rather than stress distribution, is the primary cause of the observed variations.

La3Ni2O7-delta Exhibits Robust Superconductivity

This research demonstrates the successful observation of both zero resistance and the Meissner effect within a single crystal of La3Ni2O7-delta, providing compelling dual evidence for superconductivity in this material. Utilizing nitrogen-vacancy centers in diamond as highly sensitive magnetic probes, scientists were able to map the superconducting regions and visualize sample inhomogeneities, overcoming limitations associated with traditional high-pressure magnetic measurements. The combination of electrical and magnetic characterization strengthens the case for high-temperature superconductivity in La3Ni2O7-delta and offers new insights into its structural and magnetic properties under pressure. While this study confirms superconductivity, the authors acknowledge that further work is needed to fully understand the underlying mechanisms and to improve the homogeneity of the superconducting regions within the material. Future research directions include exploring methods to enhance sample quality and to investigate the relationship between structural properties and superconducting behavior, promising to deepen our understanding of superconductivity and potentially pave the way for novel applications of this intriguing material.