In the past, various nickelate compounds have been of interest for their correlated electron properties and possible superconductivity. A particular focus is on two-dimensional Ni1+ compounds that might mimic the Cu2+ state of the superconducting cuprates. After superconductivity was discovered in some thin films of planar infinite layer nickelates, the authors investigated the trilayer nickelate Pr4Ni3O8 via ARPES.

Since ARPES is a surface-sensitive techniques, the first step was to grow a precursor compound: The high-pressure single-crystal growth of Pr4Ni3O10 was performed by optical floating-zone method at an oxygen pressure of  about 140 bar using a ScIDre HKZ furnace. By reduction, Pr4Ni3O8 was grown in bulk, cleavable crystalline form a downstream step.

With the ARPES measurements on the in situ cleaved material and other experimental data, the authors were able to compare the main physics of 1+ valence nickelates and 2+ valence cuprates. The created overview with the main physical properties of the two families contributes to a better understanding of structure-property relations.