Expanding the trilayer Ruddlesden-Popper nickelate family: Synthesis and characterization of Sm$_4$Ni$_3$O$_{10-δ}$ single crystals

The discovery of high-temperature superconductivity in Ruddlesden-Popper (RP) nickelates has attracted significant attention. Bulk superconductivity emerges under pressure in trilayer nickelates La$_4$Ni$_3$O$_{10-δ}$ (T$_c$ $\approx$ 30 K) and Pr$_4$Ni$_3$O$_{10-δ}$ (T$_c$ $\approx$ 40.5 K), where