Trilayers

A trilayer is a material or device composed of three layers stacked along a single dimension. The individual layers can differ in chemical composition, crystalline orientation, thickness, or interfacial strain. Trilayers are studied to understand how interactions between adjacent layers modify electronic, magnetic, optical, or superconducting properties and to engineer new functionalities through layer sequencing and stacking order.

In spintronics and magnetism, magnetic trilayers typically consist of two ferromagnetic layers separated by a thin nonmagnetic spacer. The spacer mediates exchange coupling that can be ferromagnetic or antiferromagnetic, depending on thickness and materials. Such trilayers underpin devices that rely on changes in resistance or magnetization, including giant magnetoresistance sensors and spin valves.

In high-temperature superconductors, certain cuprates are described as trilayer systems with three CuO2 planes per unit cell. Interlayer coupling and charge distribution across the planes influence superconducting properties, and Tc often depends on the number and arrangement of layers. Examples include Bi-based and Tl-based trilayer cuprates, with the Tc peaking near three layers in some families.

In two-dimensional materials, trilayer graphene and trilayer transition metal dichalcogenides consist of three stacked sheets. The stacking order—such as ABA (Bernal) or ABC (rhombohedral)—produces distinct electronic band structures. An external electric field can open or tune a band gap in some stackings, enabling field-effect devices and tunable optics.

Fabrication and characterization methods include sequential deposition techniques like molecular beam epitaxy and chemical vapor deposition, as well as mechanical stacking of exfoliated layers. Characterization employs X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and electrical or optical measurements to assess interlayer coupling and functional properties.