A research team led by Prof. LIU Xiaodi from the Hefei Institute of Physical Science of the Chinese Academy of Sciences, together with researchers from Jilin University and Sun Yat-sen University, has achieved simultaneous detection of zero electrical resistance and the Meissner effect in lanthanum nickelate (La₃Ni₂O_7−δ) single crystals under high pressure. 

The researchers combined diamond nitrogen-vacancy (NV) center quantum sensing with electronic transport measurements to provide unambiguous evidence of high-temperature superconductivity in this nickelate system. 

The results were published in Physical Review Letters.

Superconductivity in La₃Ni₂O_7−δ was first reported in 2023 through transport measurements, which revealed zero resistance around 80 K. However, confirming superconductivity requires detecting diamagnetism, or the expulsion of magnetic fields — the Meissner effect — which had remained elusive due to technical challenges associated with high-pressure environments and small superconducting volume fractions.

In this study, the researchers integrated NV center quantum magnetometry with a diamond anvil cell platform, enabling micron-scale, spatially resolved in situ magnetic mapping under high pressure and low temperature. 

At the same time, four-probe resistance measurements were performed on the same crystal to ensure consistent experimental conditions. This dual approach allowed the team to directly correlate localized diamagnetic responses with zero-resistance regions, thereby offering compelling evidence for bulk superconductivity in the nickelate system.

The NV center sensor exhibited high sensitivity and spatial resolution, even under extreme conditions such as pressure gradients and sample inhomogeneity. With the support of a self-built, high-pressure, low-temperature magnetic detection platform based on solid-state spin defects, the team systematically revealed how superconductivity in La₃Ni₂O_7-δ evolves with pressure.

This work confirms the high-temperature superconductivity in La₃Ni₂O_7−δ and highlights the unique advantages of NV center technology for magnetic sensing in extreme environments.

Measurement of the Meissner effect in a La₃Ni₂O_7−δ single crystal sample. (Image by LIU Xiaodi)

The resistance curve of a La₃Ni₂O_7−δ single crystal sample. (Image by LIU Xiaodi)