Evidence of filamentary superconductivity in pressurized La3Ni2O7-delta single crystals

Abstract

Since the discoveries of high-temperature superconductivity in cuprate superconductors1,2, the attempts to understand their superconducting mechanism and search for new high-temperature superconducting families have never been paused in over three decades. Recently, the signatures of superconductivity near 80 K have been discovered in the single crystal of La3Ni2O7-d under pressure3, which makes it a new candidate of the high-temperature superconductors dominated by 3d transition elements after the cuprate and iron-pnictide superconductors1,2,4, and has attracted significant attention. However, the superconductivity, characterized by the zero resistance and the Meissner effect, is anomalously irreproducible in La3Ni2O7-d. In this study, we report the experimental results obtained from highly sensitive ac susceptibility measurements, which reveal that the maximum superconducting volume fraction in the La3Ni2O7-d sample is approximately 1% (employing superconducting vanadium as a reference). In tandem with the observation of the zero-resistance state only in some of the samples, we suggest that the superconductivity in this nickelate is filamentary-like. Furthermore, from the high-pressure Hall coefficient (RH) measurements, we find that RH remains positive under pressure up to 28.8 GPa but displays a significant change in RH(P) at the critical pressure of about 10 GPa, where the superconductivity emerges, highlighting the crucial role of hole-carrier enhancement in boosting the superconductivity in La3Ni2O7-d. Our results provide new insights into understanding the puzzling questions of the high-Tc superconductivity emerging from this complex system and a clue for exploring new high-Tc superconducting materials in 3d transition metal compounds.