In-Plane Anisotropy in van der Waals NiTeSe Ternary Alloy

The anisotropic properties of materials profoundly influence their electronic, magnetic, optical, and mechanical behaviors and are critical for a wide range of applications. In this study, the anisotropic characteristics of Ni-based van der Waals materials, specifically NiTe₂ and its alloy NiTeSe, utilizing a combination of comprehensive scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) calculations, are explored. Unlike 1T-NiTe₂, which exhibits trigonal in-plane symmetry, the substitution of Te with Se in NiTe₂ (resulting in the NiTeSe alloy) induces a pronounced in-plane anisotropy. This anisotropy is clear in the STM topographs, which reveal a distinct linear order of charge distribution. Corroborating these observations, ARPES measurements and DFT calculations reveal an anisotropic Fermi surface centered at the $\overline{\Gamma }$ point, which is notably elongated along the k_y direction, leading to directional variations in in-plane carrier velocities. Consequently, the Fermi velocity is highest along the k_x direction where the linear charge distribution aligns in real space and is lowest along the k_y direction. These findings offer valuable insights into the tunability of anisotropic properties in ternary transition metal dichalcogenide systems, highlighting their potential applications in the development of anisotropic electronic and optoelectronic devices.