Identification of the superconductivity in bilayer nickelate La$_3$Ni$_2$O$_7$ upon 100 GPa

TL;DR

This study demonstrates bulk superconductivity in La$_3$Ni$_2$O$_7$ bilayer nickelates under high pressure, revealing a maximum $T_c$ of 83 K and a structural transition, with superconductivity disappearing above 80 GPa.

Contribution

First comprehensive evidence of bulk superconductivity in La$_3$Ni$_2$O$_7$ under high pressure, linking structural changes and superconducting properties.

Findings

Maximum $T_c$ of 83 K at 18 GPa

Superconductivity persists up to 80 GPa

Superconducting volume fraction up to 62.7%

Abstract

Identification of superconductivity in the Ruddlesden-Popper phases of nickelates under high pressure remains challenging. Here, we report a comprehensive study of the crystal structure, resistance, and Meissner effect in single crystals of La$_3$Ni$_2$O$_7$ with hydrostatic pressures up to 104 GPa. X-ray diffraction measurements reveal a structural transition from the orthorhombic to a tetragonal phase above 40 GPa. Zero resistance of the superconductivity was achieved with a maximum onset $T_c^{onset}$ of 83 K at 18.0 GPa. Superconductivity is gradually suppressed until it disappears above 80 GPa, resulting in a right-triangle-like superconducting region. The direct-current magnetic susceptibility technique successfully detected the Meissner effect in La$_3$Ni$_2$O$_7$ under pressure; the maximum superconducting volume fraction is estimated to be 62.7% at 22.0 GPa. Thus, we demonstrate the bulk nature of superconductivity in the bilayer nickelate La$_3$Ni$_2$O$_7$ single crystals under high pressure. The results reveal intimate connections among the superconductivity, oxygen content, and structure in La$_3$Ni$_2$O$_7$.