Superconductivity in layered nickelates has attracted attention in recent years. Under high pressure, some of these materials can reach transition temperatures as high as 80 K, while related compounds show stable superconductivity around 20 K. However, technical challenges remain in characterizing their properties, as experiments must simultaneously achieve ultra-high pressure, strong magnetic fields, and cryogenic temperatures.

In a study published in Physical ReviewX, a research team led by Prof. ZHANG Jinglei from Hefei Institutes of Physical Science of the Chinese Academy of Sciences found that the trilayer nickelate La₄Ni₃O_10-δ exhibited a nearly isotropic upper critical field under high pressure, providing insights into the superconducting mechanism of nickel-based materials.

Researchers used the water-cooled magnet WM5 at the Steady High Magnetic Field Facility, and developed a new measurement system that enables precise rotation of samples under combined extreme conditions of high pressure, strong magnetic fields, and low temperatures. They mapped the full-temperature behavior of the upper critical field in different magnetic field directions and systematically examined its anisotropy.

Researchers found that, unlike most layered superconductors which typically show strong directional dependence, this nickelate exhibited nearly isotropic behavior across the entire temperature range, which is an unusual feature for a strongly layered material.

Further analysis suggested that this behavior arose from the combined effect of two types of electronic states which contribute differently to electrical transport but in opposite ways. In particular, the two bands showed opposite anisotropy in carrier diffusivity, effectively compensating for each other. Their contributions balanced out, leading to an overall nearly isotropic superconducting response.

This work provides an experimental approach for studying quantum materials under combined extreme conditions.

Phase diagram of the superconducting upper critical field of trilayer nickelate La₄Ni₃O_10-δ along two orientations under high magnetic field. (Image by BIAN Yaolong)