  Recently, Sukbae Lee et al.reported that material
Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O (LK-99) has a series of characteristics of room
temperature superconductors, including diamagnetic transition, resistance jump,
nearly zero-resistance, magnetic field-dependent IV characteristics and so on
(10.6111/JKCGCT.2023.33.2.061, arXiv:2307.12008, arXiv:2307.12037). However,
whether LK-99 is really a room temperature superconductor is still
controversial. On the one hand, some people think that the relatively weak
diamagnetism of LK-99 reported by Sukbae Lee et al. is not the Meissner effect.
On the other hand, there are doubts about the authenticity of its
zero-resistance test results. Global replication studies have shown that LK-99
does have a large diamagnetic (arXiv:2308.01516), and also found a
zero-resistance behavior at a low temperature of 110 $^\circ$K
(arXiv:2308.01192). However, up to now, there is still no direct reproducible
evidence to support Sukbae Lee et al.'s conclusion that LK-99 is a room
temperature superconductor. Here, a distinct resistance jump was observed at
about 387 $^\circ$K under ambient pressure in our experiment for unclear reason
including possible impurity's contribution. The overall resistance of the test
LK-99 sample still shows semiconductivity, and the resistance cannot really
drop to zero. Our findings indicate that to identify the true potential of
LK-99, high quality crystals without impurity are very important.
