Phases and magnetism at microscale in compounds containing nominal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Pb</mml:mi><mml:mrow><mml:mn>10</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>Cu</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mi mathvariant="normal">P</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mn>6</mml:mn></mml:msub><mml:mi mathvariant="normal">O</mml:mi></mml:mrow></mml:math>
Chang Liu, Wenxin Cheng, Xiaoxiao Zhang, Juan Xu, Jiaxin Li, Qiuyan Shi, Changhong Yuan, Li Xu, Honglin Zhou, Shilin Zhu, Jianping Sun, Wei Wu, Jianlin Luo, Kui Jin, Yangmu Li
Abstract
Achieving superconductivity at room temperature could lead to substantial advancements in industry and technology. Recently, a compound known as Cu-doped lead-apatite, ${\mathrm{Pb}}_{10\ensuremath{-}x}{\mathrm{Cu}}_{x}{(\mathrm{P}{\mathrm{O}}_{4})}_{6}\mathrm{O} (0.9<x<1.1)$, referred to as ``LK-99,'' has been reported to exhibit unusual electrical and magnetic behaviors that appear to resemble a superconducting transition above room temperature. In this work we collected multiphase samples containing the nominal ${\mathrm{Pb}}_{10\ensuremath{-}x}{\mathrm{Cu}}_{x}{(\mathrm{P}{\mathrm{O}}_{4})}_{6}\mathrm{O}$ phase (no superconductivity was observed in our measured samples), synthesized by three independent groups, and studied their chemical, magnetic, and electrical properties at the microscale to overcome difficulties in bulk measurements. Through the utilization of optical, scanning electron, atomic force, and scanning diamond nitrogen-vacancy microscopy techniques, we were able to establish a link between local magnetic properties and specific microscale chemical phases. Our findings indicate that while the ${\mathrm{Pb}}_{10\ensuremath{-}x}{\mathrm{Cu}}_{x}{(\mathrm{P}{\mathrm{O}}_{4})}_{6}\mathrm{O}$ phase seems to have a mixed magnetism contribution, a significant fraction of the diamagnetic response can be attributed to Cu-rich regions (e.g., ${\mathrm{Cu}}_{2}\mathrm{S}$ derived from a reagent used in the synthesis). Additionally, our electrical measurements reveal the phenomenon of current path switch and a change in resistance states of ${\mathrm{Cu}}_{2}\mathrm{S}$. This provides a potential explanation for the electrical behavior observed in compounds related to ${\mathrm{Pb}}_{10\ensuremath{-}x}{\mathrm{Cu}}_{x}{(\mathrm{P}{\mathrm{O}}_{4})}_{6}\mathrm{O}$.