Cu2S likely plays an important role in the sharp resistivity transition of LK-99. Nevertheless, this immediately arouses an intriguing question of whether the extraordinary room-temperature colossal magnetoresistance in the initial reports, which has been less focused, originates from Cu2S as well. To resolve this issue, we have systematically investigated the electrical transport and magnetotransport properties of near-stoichiometric Cu2S pellets and thin films. Neither Cu2S nor LK-99 containing Cu2S in this study was found to exhibit the remarkable magnetoresistance effect implied by Lee et al. This implies that Cu2S could not account for all of the intriguing transport properties of the initially reported LK-99, and the initially reported LK-99 samples might contain magnetic impurities. Moreover, based on the crystal-structure-sensitive electrical properties of Cu2S, we have constructed a piezoelectric-strain-controlled device and obtained a giant and reversible resistance modulation of 2 orders of magnitude at room temperature, yielding a huge gauge factor of 160,000.
Keywords: Cu2S; Electroresistance; First-order phase transition; Impurity phase of LK-99; Magnetoresistance.