Capture of B31-Type MnSe_0.5Te_0.5 Phase With Structure-Borne Superconductivity Initiated by Pressure-Induced...

Superconductivity in manganese-based compounds is strongly dependent on their high-pressure phases. Consequently, capturing high-pressure superconducting phases, particularly those that cannot be crystallized in their bulk form at ambient condition yet retain superconductivity, is of significant interest. Here, we report the capture of a superconducting high-pressure B31-type MnSe_0.5Te_0.5 phase (space group Pnma) at ambient pressure, achieved via chemical substitution-induced irreversible phase transitions (Fm $\overline{3}$ m⇀P6₃/mmc⇀Pnma) and reversible spin-crossover under a hydrostatic compression-decompression cycle up to ≈40 GPa. Upon decompression, the B31 phase exhibits structure-borne superconductivity that persists down to ≈4 GPa, with a maximum T_c of ≈7.5 K at ≈8 GPa. DFT calculations reveal that the accumulated pressure-induced charge transfer (ligand-to-Mn²⁺) causes an abrupt Jahn-Teller distortion (JTD) in MnX₆ octahedra by lifting the t_2g orbital degeneracy in low-spin Mn²⁺ (d⁵). The JTD triggers Peierls-like metallic Mn-Mn dimerization, facilitating electron-pairing by driving local electron redistribution, thereby initiating superconductivity in the orthorhombic phase. These findings demonstrate an approach to retain a superconducting phase through chemical substitution-induced irreversible phase transition under high-pressure.