Pressure-induced semiconductor to metal transition and its impact on the electronic, optical, and thermodynamic properties of the new Kitaev spin liquid candidate CoI2

• Published in: Materials chemistry and physics 2024-08, Vol.322, p.129539, Article 129539
• Main Authors: Bouhmouche, A., Rhrissi, I., Moubah, R.
• Format: Article
• Language: English
• Subjects: CoI2; Kitaev physics; Optoelectronic properties; Phase transition; Pressure; Quantum spin liquid; Thermodynamic properties
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2024.129539

We investigate the recently identified Kitaev candidate, the unconventional two-dimensional (2D) crystalline material van der Waals CoI2. Our approach involves employing ab-initio calculations to study the effects of applied pressure on its physical properties. CoI2 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 CoI2 to pressure, a significant increase of the optical conductivity from 9900 to 11600 (Ω cm)−1, and the refractive index increases from 2.75 to 3.5. Our thermodynamic calculations reveal a captivating tale of CoI2; 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 CoI2. In addition, a low thermal conductivity (ranging from 5 to 0.1 W m−1 K−1) underscores the strong interactions among quantum spins. •CoI2 transitions from semiconductor to metal at 13 GPa.•Optical conductivity rises from 9900 to 11600 (Ω cm)−1 under pressure.•Refractive index increases from 2.75 to 3.5 with pressure.•Peak at 55 K in heat capacity suggests entropy variation.•Low thermal conductivity ranges from 5 to 0.1 W m−1 K−1.