Enhanced superconductivity and Spin-Orbit interaction in Bi2Se3-Doped FeSe1-xTex bulk single crystals

We investigated the structural, superconducting, magneto-transport, and ultrafast optical properties of Bi 2 Se 3 -doped FeSe 1-x Te x single crystals containing 1 % (F37B1) and 4 % (F37B4) Bi 2 Se 3 . X-ray diffraction confirmed high crystallinity with c-axis-preferred orientation. The superconducting transition temperature increased from ∼ 10 K in F37B1 to ∼ 14 K in F37B4. Magneto-transport measurements revealed characteristic weak-antilocalization behavior and a clear violation of Kohler’s rule, consistent with enhanced spin–orbit scattering and multiband charge transport. X-ray photoelectron spectroscopy verified the chemical stability of Bi incorporation without secondary phases or oxidation. Magnetic hysteresis loops confirmed the presence of robust type-II superconductivity in both samples. Ultrafast optical spectroscopy revealed doping-dependent carrier relaxation: F37B1 showed faster decay components, while F37B4 exhibited slower recombination dynamics. These findings demonstrate that Bi 2 Se 3 incorporation systematically modifies the electronic scattering environment in FeSe 1-x Te x . It also strengthens spin–orbit interactions. Together, these effects provide important insight into how dopants can tune the superconducting and dynamical properties of iron chalcogenides.