Abnormal resistance jump in Pb-Cu-P-O thin film

Pb_10-x Cu_x (PO₄)₆ O (LK-99), a potential room-temperature superconductor, has attracted the global attention since its paper was published on arXiv [1]. Many research teams are attempting to reproduce and verify LK-99, but its superconductivity remains unconfirmed. The chemical formula of LK-99 is Pb_10-x Cu_x (PO₄)₆ O, which is a hexagonal structure (P6₃/m, 176) with Cu²⁺ ions substituting for Pb²⁺ ions at the 2^nd position by approximately 1/4 in pure lead-phosphate (Pb₁₀(PO₄)₆O). For LK-99 thin film growth via molecular beam epitaxy (MBE), we selected Si (111) and Al₂O₃ substrates with mismatches of about 2%. The various growth temperatures were set after preheating at 600 ℃, and we individually adjusted the Pb and Cu ratio; x = 0.8 ~ 5. The growth process was monitored using reflection high-energy electron diffraction (RHEED). To determine the chemical composition of the sample, we analyzed it using an Energy Dispersive Spectrometer (EDS). We observed a resistance increase when it is exposed to air after growth. Interestingly, the resistance was decreased in PPMS system under vacuum (1 X 10^-2 Torr). Also we observed abnormal jump in temperature dependent resistance. In this talk, we will present on the structures, compositions, and unique transport properties of Pb-Cu-P-O compound in detail.

 

Reference

[1] S Lee, et.al., The Frist Room-Temperature Ambient-Pressure Superconductor. arXiv.2307.12008 (2023)