출처: https://www.reddit.com/r/LK99/comments/15sx1z5/lk99_apple_versus_orange/



Recently, the German group headed by B. Keimer synthesized a single crystal of LK-99 that was a translucent insulator, and that was definitely not a superconductor.


The group submitted their report to the arXiv.


My collaborator is carrying out density-functional-theory (DFT) calculations, and he mentioned to me yesterday that some relevant differences exist between the crystal structures reported by the South Korean team and the German team.


It appears that there are two types of lead atom sites: those with 4-fold rotation symmetry, and those with 6-fold rotation symmetry.


The recent german group's material substitutes lead atoms of both types with copper, while the south-Korean group's material substitutes copper on only one of the types of lead atom sites, which I believe are those with 6-fold rotation symmetry.


My collaborator believes that the two types of copper substitution will lead to different electronic properties. We shall see!


P.S. 1. Keimer's preprint: https://arxiv.org/abs/2308.06256




최근, 베른하르트 카이머가 이끄는 독일 그룹(막스플랑크 연구소)은 반투명 절연체인 LK-99 단결정을 합성했는데, 그것은 분명히 초전도체가 아니었습니다.


그 그룹은 보고서를 아카이브에 제출했습니다.


제 동료연구자는 밀도범함수이론(DFT) 계산을 수행하고 있는데, 한국 연구팀과 독일 연구팀이 보고한 결정 구조 사이에 몇 가지 차이가 있다고 어제 언급했습니다.


납 원자 사이트에는 4폴드 회전대칭형과 6폴드 회전대칭형의 두 가지 유형이 있는 것으로 보입니다.


최근 독일 연구팀의 물질은 두 가지 유형의 납 원자를 모두 구리로 치환한 반면, 한국 연구팀의 물질은 한 가지 유형의 납 원자만 구리로 치환한 것으로 추정됩니다(6폴드 회전대칭형인 것 같습니다).


제 동료연구자는 그 두 가지 유형의 구리 치환이 서로 다른 전자적 특성으로 이어질 것이라고 믿고 있습니다. 두고 봐야죠!


https://arxiv.org/abs/2308.06256

Single crystal synthesis, structure, and magnetism of Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$OThe recent claim of superconductivity above room temperature in Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O with 0.9 < $x$ < 1 (referred to as LK-99) has sparked considerable interest. To minimize the influence of structural defects and impurity phases on the physical properties, we have synthesized phase-pure single crystals with $x \sim 1$. We find that the crystals are highly insulating and optically transparent. X-ray analysis reveals an uneven distribution of the substituted Cu throughout the sample. Temperature ($T$) dependent magnetization measurements for $ 2 \leq T \leq 800$ K reveal the diamagnetic response characteristic of a non-magnetic insulator, as well as a small ferromagnetic component, possibly originating from frustrated exchange interactions in Cu-rich clusters in the Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O structure. No anomalies indicative of phase transitions are observed. We therefore rule out the presence of superconductivity in Pb$_{9}$Cu(PO$_4$)$_6$O crystals, and provide some considerations on the origin of anomalies previously reported in experiments on polycrystalline specimen.arxiv.org