Uncovering origins of heterogeneous superconductivity in La₃Ni₂O₇ using quantum sensors

La₃Ni₂O₇ is the first unconventional bulk superconductor beyond the cuprates to operate above liquid nitrogen temperatures. Unlike other nickelates, its Ni valency differs dramatically from that of analogous cuprates, challenging our understanding of the underlying conditions of high-T_c superconductivity.

La₃Ni₂O₇ requires substantial pressure (>10 GPa) to superconduct; the necessarily bulky pressure cell prevents the use of most conventional microscopic probes of superconductivity. This is deeply troubling, as traditional measurements of La₃Ni₂O₇ yield profound inconsistencies between samples. We lack an understanding of what specific conditions allow for superconductivity in this compound.

Using nitrogen vacancy (NV) quantum sensors embedded in the pressure cell, we image La₃Ni₂O₇ superconductivity via submicron-resolved maps of the Meissner effect, revealing its striking spatial heterogeneity. Using a complementary NV modality, we simultaneously image the local shear stress, and reveal that superconductivity is eliminated above a critical shear. We also correlate maps of stoichiometry to establish the chemical phase of the superconductor. This new toolkit significantly enhances our understanding of nickelate superconductivity and establishes a new paradigm of submicron-resolved metrology under pressure.