Concurrent Pressure-Induced Superconductivity and Photoconductivity Transitions in PbSeTe.

Concurrent superconductivity and negative photoconductivity (NPC) are rarely observed. Here, the discovery in PbSeTe of superconductivity and photoconductivity transitions between positive photoconductivity (PPC) and NPC during compression is reported to ≈40 GPa and subsequent decompression, which are also accompanied by reversible structure transitions (3D Fm m ⇌ 2D Pnma ⇌ 3D Pm m). Superconductivity with a maximum T of ≈6.7 K coincides with NPC and structure transition of Pnma to Pm m at ≈18 GPa and the latter phase is preserved down to ≈5 GPa with enhanced T of ≈6.9 K during decompression. The observations imply the simultaneous superconducting and photoconductive transitions are closely related to the metallic Pm m phase. First-principles calculations suggest the enhanced p-p hybridization and charge transfer between Pb-5p and ligand-p orbitals near the Fermi surface play key roles in electron-phonon interaction of mediating the Cooper pairs in PbSeTe. Hall coefficient measurements reveal that photothermal effect enhances electron-phonon interplay, which decreases carrier concentration and mobility and results in the reversal of PPC-NPC. Structure-dependent superconductivity and NPC are jointly mediated by electron-phonon interplay, which is tunable through illumination or cooling at high-pressure. The findings shed light on the origin of superconductive and photoconductive transitions in versatile materials of lead chalcogenides.