Synthesis and Characterisation of LK-99

> Current-voltage characteristics were recorded using 2614b Keithley SourceMeter and 2182A Keithley Nanovoltmeter, using either 4-terminal or van der Pauw geometry. Due to strong inhomogeneity of the samples, their current-voltage characteristics show a broad variation of response, with resistance ranging many orders of magnitude, and V-I curves showing signatures of switching, hysteresis, and nonlinearity. Samples appear to be brittle as well. Often, samples crack and break down during measurements, when high current (> 50 mA) was applied, or during mounting due to even slight mechanical vibration.

> Overall, at this stage, we can conclude that although the synthesis of LK-99 shows XRD features similar to the reported, and EDX data confirm their elemental composition, but no signatures of superconductivity are visible

> However, neither diamagnetic levitation nor zero resistance was observed in any of our LK-99 samples. In the synthesized samples, we found few very small pieces of materials, either black or pink appearance under optical microscope, with strong para- or ferromagnetic response. That is, these samples move, flip, or stand as the magnet moves underneath, similar to those reported in some videos (e.g., as in Ref. 7) in an attempt to replicate LK-99 diamagnetic levitation. We carefully separated these particles and performed EDX analysis on them. As confirmed by EDX, these magnet-responsive particles have iron inclusions (Fig. 5). This helps to explain our results with magnetic response. Unfortunately, despite all the care has been taken to avoid iron contamination during the process, some remains.