Graphene multilayers for coherent perfect absorption: effects of interlayer separation

Area of Science:

• Condensed Matter Physics
• Materials Science
• Optics

Background:

• Multilayer graphene structures exhibit unique optical absorption properties.
• Coherent Perfect Absorption (CPA) is a phenomenon of significant interest in optical applications.
• Understanding the role of interlayer separation is key to controlling optical properties.

Purpose of the Study:

• To investigate the sensitivity of multilayer graphene optical absorption to subnanometer interlayer separation.
• To derive theoretical expressions for optical absorption considering interlayer effects.
• To establish the critical interlayer separation limit (Dlim) for maintaining theoretical absorption bounds.

Main Methods:

• Utilized a transfer-matrix formalism to derive semi-analytical expressions for far-field observables.
• Developed a continued-fraction analysis for an infinite layer model.
• Compared theoretical predictions with experimental data for Van der Waals crystals.

Main Results:

• Neglecting interlayer separation yields an upper absorption bound of 50% for real conductivities, essential for CPA.
• A critical interlayer separation (Dlim), often smaller than realistic values, limits the existence of this absorption bound.
• Absorption becomes highly sensitive to interlayer separation beyond Dlim.
• Derived a closed-form expression for absorption in infinite graphene layers and for Dlim.

Conclusions:

• Subnanometer interlayer separation critically influences optical absorption in multilayer graphene.
• Accurate modeling of multilayer Van der Waals crystals for CPA requires careful consideration of interlayer separations.
• Treating layers as electronically independent is valid only up to a certain interlayer separation.