Quantum sensing with nitrogen-vacancy (NV) centers in diamond enables the characterization of magnetic properties in the extreme situation of a tiny sample with defects. Recent studies have reported superconductivity in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_{7\text{−}\delta }$ under pressure, with zero resistance near 80 K, though the Meissner effect remains debated due to low superconducting volume fractions and limited high-pressure magnetic measurement techniques. In this work, we use diamond quantum sensors and four-probe detection to observe both zero resistance and the Meissner effect in the same ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_{7\text{−}\delta }$ single crystal. By mapping the Meissner effect, we visualized superconducting regions and revealed sample inhomogeneities. Our combined magnetic and electrical measurements on the same crystal provide dual evidence of superconductivity, supporting the high-temperature superconductivity of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_{7\text{−}\delta }$. This study also offers insights into its structural and magnetic properties under high pressure.

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• Methods in superconductivity