Optical Absorption in Indirect Semiconductor to Semimetal PtSe_{2} Arises from Direct Transitions.

Area of Science:

• Condensed Matter Physics
• Materials Science
• 2D Materials

Background:

• Platinum diselenide (PtSe2) exhibits thickness-dependent electronic properties, transitioning from semiconductor to semimetal.
• Its optical absorption edge has been theoretically attributed to indirect interband transitions.

Purpose of the Study:

• To determine the origin of the optical absorption threshold in PtSe2.
• To clarify the role of direct vs. indirect transitions in the material's electronic behavior.
• To investigate the influence of thickness, stacking, and excitons on optical absorption.

Main Methods:

• Broadband optical absorption spectroscopy (0.8-3.0 eV) on exfoliated PtSe2 crystals.
• Density Functional Theory (DFT) ab initio simulations.
• Quantitative comparison of experimental data and theoretical calculations.

Main Results:

• Experimental and theoretical results confirm that optical absorption in PtSe2 originates exclusively from direct electronic transitions.
• The study refutes the previous conjecture attributing the absorption threshold to indirect transitions.
• Established a clear understanding of the electronic transitions governing PtSe2's optical properties.

Conclusions:

• The optical absorption of PtSe2 is dominated by direct transitions, regardless of thickness.
• This finding provides crucial insight into the semiconductor-to-semimetal transition mechanism in this 2D material.
• Opens avenues for exploring excitonic effects and stacking configurations in PtSe2.