Multiple Superconducting Phases in m-TaS₃ under Extreme Compression

Quasi-one-dimensional transition metal trichalcogenides (TMTCs) provide a fertile platform to explore superconductivity under extreme conditions. However, the superconducting transition temperatures (T_c) reported for TMTCs to date remain below 10 K. Monoclinic TaS₃ (m-TaS₃) has been theoretically predicted as a candidate for pressure-induced superconductivity. Herein, we use in situ high-pressure transport and synchrotron X-ray diffraction (XRD) measurements to construct the complete superconducting phase diagram of m-TaS₃, revealing three distinct superconducting regions over a broad pressure range of 5.7-210 GPa. Notably, robust superconductivity with a record T_c of 17.4 K emerges in the high-pressure P2₁/m (HP-P2₁/m) phase. This behavior was associated with an isosymmetric transformation near 88.5 GPa, which flattens the TaS₆ triangular prism, enhances structural uniformity, and promoting strong d-p orbital hybridization, leading to an increased density of states at the Fermi level and improved Fermi surface nesting. The resulting enhancement of electron-phonon coupling, driven by both structural and electronic reconfiguration, accounts for the elevated superconducting transition temperature in the HP-P2₁/m phase. These findings not only deepen our understanding of the electronic behavior of TMTCs under extreme conditions but also provide a valuable framework for exploring superconductivity in low-dimensional systems.