# Uncovering origins of heterogeneous superconductivity in La3Ni2O7

## TL;DR

This study uses quantum sensing to reveal that superconductivity in La3Ni2O7 is inhomogeneous at the micrometer scale, linked to local stress and composition.

## Contribution

The paper introduces wide-field quantum sensing to map μm-scale superconducting inhomogeneity and correlate it with stress and stoichiometry in high-pressure nickelates.

## Key findings

- La3Ni2O7 exhibits inhomogeneous superconducting responses at the micrometer scale.
- Local diamagnetic responses correlate with tensorial stress and stoichiometric composition.
- The study identifies mechanisms that suppress or enhance superconductivity in nickelates.

## Abstract

The family of nickelate superconductors have long been explored as analogues of the high-temperature cuprates1–6. Nonetheless, the recent discovery that certain stoichiometric nickelates superconduct up to high critical temperatures (Tc) under pressure came as a surprise7–13. The mechanisms underlying the superconducting state remain experimentally unclear. Apart from the practical challenges posed by working in a high-pressure environment, typical samples exhibit anomalously weak diamagnetic responses, which have been conjectured to reflect inhomogeneous ‘filamentary’ superconducting states7,9,14–17. Here we perform wide-field, high-pressure, optically detected magnetic resonance spectroscopy to image the local diamagnetic responses of as-grown La3Ni2O7 samples in situ, using nitrogen vacancy quantum sensors embedded in the diamond anvil cell18–23. These maps confirm marked inhomogeneity of the functional superconducting responses at the few μm scale. By spatially correlating the diamagnetic Meissner response with both the local tensorial stress environment, also imaged in situ, and stoichiometric composition, we show the dominant mechanisms suppressing and enhancing superconductivity. Our wide-field technique simultaneously provides a broad view of sample behaviour and excellent local sensitivity, enabling the rapid construction of multi-parameter phase diagrams from the local structure–function correlations observed at the sub-μm pixel scale.

Wide-field quantum sensing shows μm-scale inhomogeneous superconductivity in high-pressure La3Ni2O7, linking local diamagnetic response to stress and stoichiometry and clarifying mechanisms that suppress or enhance superconductivity.