Two-dimensional kagome semiconductor Sc₆S5X₆ (X=Cl, Br, I) with trilayer kagome lattice

Two-dimensional (2D) multilayer kagome materials hold significant research value in the fields of regulating kagome physical properties and exploring quantum effects. However, their development is hindered by the scarcity of material systems, making the development of novel 2D multilayer kagome candidates of great importance. In this work, three types of 2D materials with trilayer kagome lattice, namely Sc 6 S 5 X 6 (X = Cl, Br, and I), have been predicted based on first-principles calculations. These 2D materials feature two kagome lattices composed of Sc atoms and one kagome lattice composed of S atoms. Stability analysis indicates that these materials can exist as free-standing 2D materials. Electronic structure calculations reveal that Sc 6 S 5 X 6 are all narrowbandgap semiconductors (0.76~0.95 eV), with band structures unveiling flat bands contributed by Sc-based kagome lattices and Dirac band gaps resulting from symmetry breaking. The sulfur-based kagome lattice in the central layer contributes an independent flat band below the Fermi level. Additionally, Sc 6 S 5 X 6 exhibit high carrier mobility, with hole and electron mobilities reaching up to 103 cm 2 V -1 s -1 , showing potential for applications in low-dimensional electronic devices. This work provides an excellent example for the development of novel multilayer 2D kagome materials.