Pressure-induced semiconductor to metal transition and its impact on the electronic, optical, and thermodynamic properties of the new Kitaev spin liquid candidate CoI 2

We investigate the recently identified Kitaev candidate, the unconventional two-dimensional (2D) crystalline material van der Waals CoI 2 . Our approach involves employing ab-initio calculations to study the effects of applied pressure on its physical properties. CoI 2 was found to be a semiconductor with a band gap energy of 2.1 eV. By applying pressure up to 13 GPa, a transition from a semiconductor to a metallic state takes place. This transition was explained by the displacement of the initially filled 5p-iodide band, overlapping with partially filled Co -3d states, leading to the formation of a hybridized conduction band and the emergence of a metallic ground state. Furthermore, by subjecting the CoI 2 to pressure, a significant increase of the optical conductivity from 9900 to 11600 ( Omega cm) -1 , and the refractive index increases from 2.75 to 3.5. Our thermodynamic calculations reveal a captivating tale of CoI 2 ; detecting a peak at 55 K in the temperature-normalized heat capacity which suggests the presence of entropy variation in the material, indicating a shift in the spin configuration within CoI 2 . In addition, a low thermal conductivity (ranging from 5 to 0.1 W m -1 K - 1 ) underscores the strong interactions among quantum spins.