One-Dimensional Excitonic Insulator of M₆Te₆ (M = Mo, W) Atomic Wires

Coulomb attraction with weak screening can trigger spontaneous exciton formation and condensation, resulting in a strongly correlated many-body ground state, namely, the excitonic insulator. One-dimensional (1D) materials natively have ineffective dielectric screening. For the first time, we demonstrate the excitonic instability of single atomic wires of transition metal telluride M₆Te₆ (M = Mo, W), a family of 1D van der Waals (vdW) materials accessible in the laboratory. The many-body GW and Bethe-Salpeter equation scheme shows giant exciton binding energies up to 1.6 eV for these narrow-gap semiconductors, much exceeding their single-particle band gaps and implying a robust thermal-equilibrium exciton Bose-Einstein condensation with high critical temperatures. The excitonic instability of these single atomic wires is attributed to their small dielectric constant, same parity and ultraflat dispersion for the band edge states. Our work shed light in exploiting the strong excitonic effects in 1D vdW materials to realize macroscopic quantum phenomena.