From semiconductor to Fermi metal and emergent density-wave-like transition in the quasi-one-dimensional n -type Bi19S27I3</mml:…

We report on crystal growth and physical properties of the quasi-one-dimensional compound Bi₁₉S₂₇I₃ by combining crystal structure, electrical resistivity, magnetic properties, Seebeck coefficient, Hall coefficient as well as hydrostatic pressure effect up to 11.5 GPa. Unlike p-type Bi₁₉S₂₇I₃ crystals, the maximum size of high-quality n-type Bi₁₉S₂₇I₃ crystals can reach 2--3 mm by optimizing the chemical vapor transport method. The measurement results indicate that Bi₁₉S₂₇I₃ is a diamagnetic semiconductor with two thermal activation energies, a large one Eg1~0.81 eV and a small one Eg2~0.36 eV, a huge room-temperature Seebeck coefficient of {-}1000 {}V/K, and improved thermoelectric power factor ~2.20.16em0exW0.16em0excm^-10.16em0exK^-2 owing to the enhanced electrical conductivity. Under pressure, Bi₁₉S₂₇I₃ undergoes a semiconductor-to-metal transition, and the thermal activation energy continuously decreases to almost zero near a critical pressure of 4.25 GPa. Accompanying this process, a density-wave-like transition emerges, characterized by the reversible jump observed in the temperature dependence of the resistivity. As the pressure further increases, the resistivity undergoes a crossover from a Fermi metal to a low-temperature upturn below a characteristic temperature, which decreases from 81 K at 4.5 GPa to 37 K at 11.5 GPa. The upturn in resistivity has a linear dependence on the logarithmic temperature, but does not saturate at low temperatures, which basically excludes a Kondo-like state and indicates the possibility of Anderson weak localization. High-pressure synchrotron x-ray diffraction confirms the absence of structural transition for $P<12.05$ GPa at room temperature, supporting pressure-induced electronic transition. Our density functional theory calculation on the assumption that the Bi1 occupies an average of ~1/6 contradicts experimental electron bands, indirectly indicating that Bi1 should be partially ordered and has many vacancies in Bi₁₉S₂₇I₃. Our results provide good examples for studying the mechanism of semiconductor metallization and exploring thermoelectric functional properties in low-dimensional materials.