Twistronics

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.

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 1.1^o relative to one another changes graphene from a normally metallic material into a superconductor.

Researchers at Columbia University in the US have developed a new 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, which are carried out on a single structure rather than multiple ones (as was the case before), could advance the emerging field of "twistronics" - a fundamentally new approach to device engineering.

"Simply varying the angle between 2D material layers thus means that graphene can be tuned from being metallic to semiconducting. Indeed, researchers at the Massachusetts Institute of Technology (MIT) recently discovered that placing two layers of graphene together, but rotated relative to one another at the 'magic' angle of 1.1° turns the normally metallic material into a superconductor."

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 fundamentally new direction in device engineering, he adds.

"Until now, we have only studied graphene and boron nitride but there exists a large class of 2D materials that can be integrated with one another in similar ways. These materials can be metallic, insulating, semiconducting, magnetic and superconducting.

"At the most basic level, our study shows that there is a fundamentally new way to control these materials that just doesn't exist in conventional semiconductor heterostructures. It therefore opens the door to a whole new field of research in which material properties can be varied by simply twisting material layers."

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.

Researchers at Columbia UniversityColumbia University in the US have developed a new 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, which are carried out on a single structure rather than multiple ones (as was the case before), could advance the emerging field of "twistronics" - a fundamentally new approach to device engineering.

Researchers at Columbia University in the US have developed a new 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, which are carried out on a single structure rather than multiple ones (as was the case before), could advance the emerging field of "twistronics" - a fundamentally new approach to device engineering.

"Simply varying the angle between 2D material layers thus means that graphene can be tuned from being metallic to semiconducting. Indeed, researchers at the Massachusetts Institute of Technology (MIT) recently discovered that placing two layers of graphene together, but rotated relative to one another at the 'magic' angle of 1.1° turns the normally metallic material into a superconductor."

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 fundamentally new direction in device engineering, he adds.

"Until now, we have only studied graphene and boron nitride but there exists a large class of 2D materials that can be integrated with one another in similar ways. These materials can be metallic, insulating, semiconducting, magnetic and superconducting.

"At the most basic level, our study shows that there is a fundamentally new way to control these materials that just doesn't exist in conventional semiconductor heterostructures. It therefore opens the door to a whole new field of research in which material properties can be varied by simply twisting material layers."