Twistronics is an approach to device engineering in which the twist angle between layers of 2D materials such as graphene affects their electronic, optical and mechanical properties.
Researchers at Columbia University in the US developed a device structure in which they can vary the "twist" angle between layers of 2D materials (such as graphene) and study how this angle affects their electronic, optical and mechanical properties. The measurements are carried out on a single structure rather than multiple ones.
Achieving this variety of electronic properties in conventional materials normally requires changing their chemical composition. The ability to vary the electronic property of a 2D material simply by altering the twist angle between its layers is therefore a new direction in device engineering.
Graphene, which is a 2D sheet of carbon atoms, does not normally have a band gap. Sets of possible electron states form regions called bands and sets of electron states that are not possible form bandgaps. Semiconductors like silicon have a narrow gap between the two bands. Electrons can jump across the gap when excited. When light strikes a solar cell, electrons can jump from the valence band to the conduction band where it forms part of the electric current. 2D graphene can develop a band gap when placed in contact with another 2D material with a closely matching lattice constant, hexagonal boron nitride. Together the graphene and boron nitride layers form a large Moiré superlattice. Two layers of graphene rotated at an angle of 1.1o relative to one another changes graphene from a normally metallic material into a superconductor.
