Spintronics

Researchers at Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley have developed a method to stabilize the edges of graphene nanoribbons and directly measure their unique magnetic properties.

The team, co-led by Felix Fischer and Steven Louie from Berkeley Lab’s Materials Sciences Division, found that by substituting some of the carbon atoms along the ribbon’s zigzag edges with nitrogen atoms, they could discretely tune the local electronic structure without disrupting the magnetic properties. This subtle structural change further enabled the development of a scanning probe microscopy technique for measuring the material’s local magnetism at the atomic scale.

The German Research Foundation (Deutsche Forschungsgemeinschaft DFG) has announced its plan to establish a new research group: "Proximity-induced correlation effects in low-dimensional structures", under the leadership of Chemnitz University of Technology. The research group will be funded with approximately 3.2 million euros plus a 22 percent program allowance for indirect costs during the first four-year funding period.

The research work of the interdisciplinary DFG research group will focus on atomically thin carbon films such as graphene. "These two-dimensional materials and their heterostructures are currently being intensively researched worldwide, as they exhibit unusual and novel electronic properties. The goal of the scientists in our DFG research group is to investigate the correlation effects occurring in a prototypical 2D heterosystem and to manipulate them in a targeted manner", said Prof. Dr. Christoph Tegenkamp from Chemnitz U, spokesperson for the new group. This involves specially fabricated epitaxial graphene layers on the semiconductor material silicon carbide. "These research should provide further foundations for novel quantum materials with tailored properties and their application, for example in spintronics or electronics".

Researchers at MIT and Harvard University have previously found that graphene can have exotic properties when situated at a 'magic angle'. Now, a new study by some of the members of the same team shows that this material could also be a "spin-triplet" superconductor one that isn't affected by high magnetic fields which potentially makes it even more useful.

"The value of this experiment is what it teaches us about fundamental superconductivity, about how materials can behave, so that with those lessons learned, we can try to design principles for other materials which would be easier to manufacture, that could perhaps give you better superconductivity," says physicist Pablo Jarillo-Herrero, from the Massachusetts Institute of Technology (MIT).

Two recent studies by a collaborative team of scientists from two NCCR MARVEL labs have identified a new type of defect as the most common source of disorder in on-surface synthesized graphene nanoribbons (GNRs).

Combining scanning probe microscopy with first-principles calculations allowed the researchers to identify the atomic structure of these so-called "bite" defects and to investigate their effect on quantum electronic transport in two different types of graphene nanoribbon. They also established guidelines for minimizing the detrimental impact of these defects on electronic transport and proposed defective zigzag-edged nanoribbons as suitable platforms for certain applications in spintronics.

Researchers from France, South Korea, and Japan have created a graphene-based beam splitter for electronic currents. The tunable device’s operation is directly comparable to that of an optical interferometer. The team believes that the technology could enable electron interferometry to be used in nanotechnology and quantum computing.
Quantum Hall valley splitter - schematic representation of the p − n junction. Image from article

An optical interferometer splits a beam of light in two, sending each beam along a different path before recombining the beams at a detector. The measured interference of the beams at the detector can be used to detect tiny differences in the lengths of the two paths. Recently, physicists have become interested in doing a similar thing with currents of electrons in solid-state devices, taking advantage of the fact that electrons behave similarly to waves in the quantum world.

An international research team, led by the University at Buffalo, has reported an advancement that could help give graphene magnetic properties. The researchers describe in their work how they paired a magnet with graphene, and induced what they describe as artificial magnetic texture in the nonmagnetic material.

The image shows eight electrodes around a 20-nanometer-thick magnet (white rectangle) and graphene (white dotted line). Credit: University at Buffalo.

Independent of each other, graphene and spintronics each possess incredible potential to fundamentally change many aspects of business and society. But if you can blend the two together, the synergistic effects are likely to be something this world hasn’t yet seen, says lead author Nargess Arabchigavkani, who performed the research as a PhD candidate at UB and is now a postdoctoral research associate at SUNY Polytechnic Institute.

A research team led by the University of Washington recently reported that carefully constructed stacks of graphene can exhibit highly correlated electron properties. The team also found evidence that this type of collective behavior likely relates to the emergence of exotic magnetic states.

We’ve created an experimental setup that allows us to manipulate electrons in the graphene layers in a number of exciting new ways, said co-senior author Matthew Yankowitz, a UW assistant professor of physics and of materials science and engineering. Yankowitz led the team with co-senior author Xiaodong Xu, a UW professor of physics and of materials science and engineering.

Scientists at EPFL have recently published a research that could open up new pathways to boosting the capacity of sodium-ion batteries. Lithium is becoming a critical material as it is used extensively in cell-phones and car batteries, while, in principle, sodium could be a much cheaper, more abundant alternative, says Ferenc Simon, a visiting scientist in the group of László Forró at EPFL. This motivated our quest for a new battery architecture: sodium doped graphene.

Since sodium is far more abundant than lithium, and the risk of fire is much lower with this battery chemistry, it is considered a potentially viable replacement to current lithium-ion technology. But sodium also has much lower energy density than lithium, which has so far limited uptake, particularly in the electric vehicle and consumer electronics segments, where the physical size of the battery is a deciding factor. EPFL's new work uses graphene to address this issue.

A team of researchers at Princeton has looked for the origins of the unusual behavior known as magic-angle twisted bilayer graphene, and detected signatures of a cascade of energy transitions that could help explain how superconductivity arises in this material.

"This study shows that the electrons in magic-angle graphene are in a highly correlated state even before the material becomes superconducting, "said Ali Yazdani, Professor of Physics and the leader of the team that made the discovery. "The sudden shift of energies when we add or remove an electron in this experiment provides a direct measurement of the strength of the interaction between the electrons."

The Graphene Flagship has announced 16 New FLAG-ERA projects, that cover a broad range of topics, from fundamental to applied research. These projects which will become Partnering Projects of the Graphene Flagship receiving around €11 million in funding overall.

Bringing together a diverse range of European knowledge and expertise, FLAG-ERA is an ERA-NET (European Research Area Network) initiative that aims to create synergies between new research projects and the Graphene Flagship and Human Brain Project.