Temperature-induced first-order electronic topological transition in β-Ag2Se.

β-Ag₂Se is a promising material for room temperature thermoelectric applications and magneto-resistive sensors. However, no attention was paid earlier to the hysteresis in the temperature dependence of resistivity [ρ(T)]. Here, we show that a broad hysteresis above 35 K is observed not only in ρ(T), but also in other electronic properties such as Hall coefficient [R_H(T)], Seebeck coefficient, thermal conductivity, and ultraviolet photoelectron spectra (UPS). We also show that the hysteresis is not associated with a structural transition. The ρ(T) and R_H(T) show that β-Ag₂Se is semiconducting above 300 K, but metallicity is retained below 300 K. While electronic states are absent in the energy range from the Fermi level (E_F) to 0.4 eV below the E_F at 300 K, a distinct Fermi edge is observed in the UPS at 15 K suggesting that the β-Ag₂Se undergoes an electronic topological transition from a high-temperature semiconducting state to a low-temperature metallic state. Our study reveals that a constant and moderately high thermoelectric figure of merit in the range 300–395 K is observed due to the broad semiconductor to metal transition in β-Ag₂Se. [ABSTRACT FROM AUTHOR]