Zero resistance and strange metal behavior of hightemperature superconducting material La₃Ni₂O₇

In 2023, signatures of pressure-induced high temperature superconductivity with an onset transition at 80K were observed in La₃Ni₂O₇. However, the absence of zero resistance cast doubts on its superconductivity. By using a recently developed quasi-hydrostatic pressure technique based on a diamond anvil cell, our group successfully observed a sharp superconducting transition with a zero resistance below 40K, providing a crucial evidence for establishing the existence of high-temperature superconductivity in La₃Ni₂O₇. Furthermore, a pronounced linear-temperature dependent resistivity is observed above its superconducting transition, suggesting an unconventional nature of its superconducting pairing state. Beside the discovery of zero resistance, our transport studies also revised the pressure-temperature phase diagram of La₃Ni₂O₇. It is found that La₃Ni₂O₇ remains metallic under pressure and there is no evidence for a metal-insulator transition if the samples are properly handled during preparations. Upon increasing pressure, the density wave transition, observed near 130K at ambient pressure, is quickly suppressed. Around 13.7GPa, evidence for a pressure-induced structural phase transition is observed near 250 K, followed by a superconducting transition with an onset temperature at Tconset≈37.5K. Tc initially increases with increasing pressure, reaching a maximum value of Tconset≈66K at 20.5GPa. On the other hand, the slope A' of the T-linear resistivity above Tc monotonically decreases with increasing pressure, showing a relation of Tc ∝ √A' above 20.5GPa, which is similar to those recently observed in the cuprate oxides. Furthermore, the inverse Hall coefficient 1/RH, derived from the Hall resistance measurements, reveal a notable increase above 15 GPa upon entering the high pressure phase, suggesting a substantial increase of the carrier concentrations in the superconducting regime, which is further supported by band structure calculations. In this article, we present a brief summary of our research progresses, and compare them with those observed in other nickelate superconductors.