Charge Density Wave and Superconductivity in BaSbTe₂S Heterolayer Crystal with 2D Te Square Nets

Low-dimensional materials with charge density waves (CDW) are attractive for their potential to exhibit superconductivity and nontrivial topological electronic features. Here we report the two-dimensional (2D) chalcogenide, BaSbTe₂S which acts as a new platform hosting these phenomena. The crystal structure of BaSbTe₂S is composed of alternating atomically thin Te square-net layers and double rock-salt type [(SbTeS)₂]^2- slabs separated with Ba²⁺ atoms. Due to the electronic instability of the Te square net, an incommensurately modulated structure is triggered and confirmed by both single-crystal X-ray diffraction, electron diffraction, and the presence of an energy bandgap in this compound. Our first-principles electronic structure analysis and investigation of structural dynamical instability suggest that the Te network plays a dominant role in its origin. The incommensurate structure is refined with a modulation vector of = 0.351(1)b* using an orthorhombic cell of a = 4.4696(5) Å, b = 4.4680(5) Å, and c = 15.999(2) Å under superspace group Pmm2(0β0)000 at 293 K. The modulation vector varies as a function of both occupancy of Te in the square net and temperature, indicating the CDW order can be modulated by local distortions. The CDW can be suppressed by pressure, leading to the emergence of superconductivity with a T_c up to 7.5 K at 13.6 GPa, suggesting a competition between the CDW order and superconductivity. Furthermore, electrical transport under the magnetic field reveals the existence of compensated high mobility electron- and hole-bands near the Fermi surface (μ ∼600-3500 cm²V^-1s^-1), suggesting Dirac-like band dispersion.