The intrinsically low lattice thermal conductivity of monolayer T-Au 6 X 2 (X = S, Se and Te).

Thermal conductivity ( κ , which consists of electronic thermal conductivity κ e and lattice thermal conductivity κ l ), as an essential parameter in thermal management applications, is a critical physical quantity to measure the heat transfer performance of materials. To seek low- κ materials for heat-related applications, such as thermoelectric materials and thermal barrier coatings. In this study, based on a complex cluster design, we report a new class of two-dimensional (2D) transition metal dichalcogenides (TMDs): T-Au 6 X 2 (X = S, Se, and Te) with record ultralow κ l values. At room temperature, the κ l values of T-Au 6 S 2 , T-Au 6 Se 2 , and T-Au 6 Te 2 are 0.25 (0.23), 0.30 (0.21), and 0.12 (0.10) W m -1 K -1 along the x -axis ( y -axis) direction, respectively, exhibiting good thermal insulation. The ultralow κ l originates from strong phonon softening and suppression, especially for the phonon with frequency 0-1 THz. In addition, T-Au 6 Te 2 holds the lowest group velocity and phonon relaxation time among the three T-Au 6 X 2 monolayers. Our study provides an alternative approach for achieving ultralow κ l through complex cluster replacement. Meanwhile, this new class of TMDs is expected to shine in thermal insulation and thermoelectricity due to their ultralow κ l values.