Concurrent Pressure-Induced Superconductivity and Photoconductivity Transitions in PbSe<sub>0.5</sub>Te<sub>0.5</sub>.
basic_science · Level V
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- Also identified by DOI 10.1002/adma.202417597.
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Abstract
Concurrent superconductivity and negative photoconductivity (NPC) are rarely observed. Here, the discovery in PbSe<sub>0.5</sub>Te<sub>0.5</sub> 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 <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mover><mn>3</mn> <mo>¯</mo></mover> <annotation>${{\bar{3}}}$</annotation></semantics> </math> m ⇌ 2D Pnma ⇌ 3D Pm <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mover><mn>3</mn> <mo>¯</mo></mover> <annotation>${{\bar{3}}}$</annotation></semantics> </math> m). Superconductivity with a maximum T<sub>c</sub> of ≈6.7 K coincides with NPC and structure transition of Pnma to Pm <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mover><mn>3</mn> <mo>¯</mo></mover> <annotation>${{\bar{3}}}$</annotation></semantics> </math> m at ≈18 GPa and the latter phase is preserved down to ≈5 GPa with enhanced T<sub>c</sub> of ≈6.9 K during decompression. The observations imply the simultaneous superconducting and photoconductive transitions are closely related to the metallic Pm <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mover><mn>3</mn> <mo>¯</mo></mover> <annotation>${{\bar{3}}}$</annotation></semantics> </math> 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 PbSe<sub>0.5</sub>Te<sub>0.5</sub>. 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.