New Method to Add Electrical Charge to Atomically Thin Graphene Device

At Washington University in St. Louis, a group of physicists has found ways to add electrical charge locally to an atomically thin graphene device by adding multiple layers of flakes of another thin material called alpha-RuCl₃ over it.

In a study published in the Nano Letters journal, the researchers offer a detailed description of the charge transfer process. It is crucial to gain control over the flow of electrical current through atomically thin materials for ensuring potential future applications in computing or photovoltaics.

In my field, where we study van der Waals heterostructures made by custom-stacking atomically thin materials together, we typically control charge by applying electric fields to the devices. But here it now appears we can just add layers of RuCl₃. It soaks up a fixed amount of electrons, allowing us to make ‘permanent’ charge transfers that don’t require the external electric field.

Erik Henriksen, Assistant Professor of Physics, School of Arts & Sciences, Washington University in St. Louis

Henriksen is the corresponding author of the new study, together with Ken Burch from Boston College. The second author of the study is Jesse Balgley, who is a graduate student in Henriksen’s laboratory at Washington University.

Computational work and calculations were performed by Li Yang, professor of physics, and his graduate student Xiaobo Lu, both of whom are from Washington University and are the co-authors of the study.

Physicists who investigate condensed matter focus much on alpha-RuCl₃ since they would like to leverage some of its antiferromagnetic properties for quantum spin liquids. In the new study, the team reports that alpha-RuCl₃ has the potential to transfer charge to materials of many different types—not only graphene, which is Henriksen’s personal favorite.

The researchers also discovered that it is sufficient to place only a single layer of alpha-RuCl₃ on top of their devices to produce and transfer charge. The process works even when a thin sheet of electrically insulating material is slipped between the graphene and the RuCl₃.

We can control how much charge flows in by varying the thickness of the insulator. Also, we are able to physically and spatially separate the source of charge from where it goes—this is called modulation doping.

Erik Henriksen, Assistant Professor of Physics, School of Arts & Sciences, Washington University in St. Louis

The addition of charge to a quantum spin liquid is one mechanism considered to be fundamental to the physics of high-temperature superconductivity.

Anytime you do this, it could get exciting. And usually you have to add atoms to bulk materials, which causes lots of disorder. But here, the charge flows right in, no need to change the chemical structure, so it’s a ‘clean’ way to add charge.

Erik Henriksen, Assistant Professor of Physics, School of Arts & Sciences, Washington University in St. Louis

Journal Reference:

Wang, Y., et al. (2021) Modulation Doping via a Two-Dimensional Atomic Crystalline Acceptor. Nano Letters. doi.org/10.1021/acs.nanolett.0c03493.