Spintronics

Researchers from the National University of Singapore (NUS), and Czech Academy of Sciences recently developed a new design concept for creating next-generation carbon-based quantum materials, in the form of a tiny magnetic nanographene with a unique butterfly-shape hosting highly correlated spins. This new design has the potential to accelerate the advancement of quantum materials which are pivotal for the development of quantum computing technologies.

A visual impression of the magnetic “butterfly” hosting four entangled spins on “wings” (left) and its corresponding atomic-scale image obtained using scanning probe microscopy (right). Image credit: NUS

Magnetic nanographene, a tiny structure made of graphene molecules, exhibits remarkable magnetic properties due to the behavior of specific electrons in the carbon atoms’ π-orbitals. By precisely designing the arrangement of these carbon atoms at the nanoscale, control over the behavior of these unique electrons can be achieved. This renders nanographene highly promising for creating extremely small magnets and for fabricating fundamental building blocks needed for quantum computers, called quantum bits or qubits.

Researchers from Helmholtz-Zentrum Dresden-Rossendorf, Universität Duisburg-Essen, CENTERA Laboratories, Indian Institute of Technology, University of Maryland and the U.S. Naval Research Laboratory have used graphene disks to demonstrate light-induced transient magnetic fields from a plasmonic circular current with extremely high efficiency. 

The effective magnetic field at the plasmon resonance frequency of the graphene disks (3.5 THz) is evidenced by a strong ( ~ 1°) ultrafast Faraday rotation ( ~ 20 ps). In accordance with reference measurements and simulations, the team estimated the strength of the induced magnetic field to be on the order of 0.7 T under a moderate pump fluence of about 440 nJ cm⁻².

Researchers at the National University of Singapore (NUS), University of Science and Technology of China and the National Institute for Materials Science in Japan have developed a way to induce and directly quantify spin splitting in two-dimensional materials.

Using this concept, they have experimentally achieved large tunability and a high degree of spin-polarization in graphene. This research achievement can potentially advance the field of two-dimensional (2D) spintronics, with applications for low-power electronics.

Researchers from Germany's RWTH Aachen University, Forschungszentrum Jülich and Japan's National Institute for Materials Science (NIMS) have found that bilayer graphene allows the realization of electron–hole double quantum dots that exhibit near-perfect particle–hole symmetry. Moreover, They showed that particle–hole symmetric spin and valley textures lead to a protected single-particle spin-valley blockade that will allow robust spin-to-charge and valley-to-charge conversion, which are essential for the operation of spin and valley qubits.

Quantum dots in semiconductors such as silicon or gallium arsenide are considered great candidates for hosting quantum bits in future quantum processors. The recent study essentially shows that bilayer graphene has even more to offer than other materials. The double quantum dots the researchers have created are characterized by a nearly perfect electron-hole-symmetry that allows a robust read-out mechanism – one of the necessary criteria for quantum computing. 

A research team at Chalmers University of Technology, Lund University and Uppsala University in Sweden have managed to create a device made of a two-dimensional magnetic quantum material that can work in room temperature. Quantum materials with magnetic properties are believed to pave the way for ultra-fast and considerably more energy efficient computers and mobile devices, but until now, these types of materials tended to only work in extremely cold temperatures. 

The group of researchers has been able to demonstrate, for the very first time, a new two-dimensional magnetic material-based device at room temperature. They used an iron-based alloy (Fe₅GeTe₂) with graphene which can be used as a source and detector for spin polarized electrons. The breakthrough is believed to enable a range of technical applications in several industries as well as in our everyday lives.

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.