Graphene

Scientists from TU Delft National Institute for Materials Science, University of Valencia, University of Regensburg and Harvard University have observed quantum spin currents in graphene for the first time without using magnetic fields. These currents are important for spintronics and could promote technologies like quantum computing and advanced memory devices.

Quantum physicist Talieh Ghiasi has demonstrated the quantum spin Hall (QSH) effect in graphene for the first time without any external magnetic fields. The QSH effect causes electrons to move along the edges of the graphene without any disruption, with all their spins pointing in the same direction. “Spin is a quantum mechanical property of electrons, which is like a tiny magnet carried by the electrons, pointing up or down”, Ghiasi explains. “We can leverage the spin of electrons to transfer and process information in so-called spintronics devices. Such circuits hold promise for next-generation technologies, including faster and more energy-efficient electronics, quantum computing, and advanced memory devices.”

Researchers at the National Graphene Institute at the University of Manchester have announced milestone in the field of quantum electronics with their latest work on spin injection to graphene. The team reported ballistic injection of spin polarized carriers via one-dimensional contacts between magnetic nanowires and a high mobility graphene channel. 

The nanowire-graphene interface defines an effective constriction that confines charge carriers over a length scale smaller than that of their mean free path. This is evidenced by the observation of quantized conductance through the contacts with no applied magnetic field and a transition into the quantum Hall regime with increasing field strength. These effects occur in the absence of any constriction in the graphene itself and occur across several devices with transmission probability in the range T = 0.08 − 0.30.

Researchers from China's Tianjin University, Fudan University, University of Chinese Academy of Sciences, National Center for Nanoscience and Technology and Tsinghua University have introduces a new technique, called the "Wax-aided immersion method," to produce controllable chiral graphene rolls. This advancement provides a novel approach to chirality modulation in two-dimensional materials and their potential applications in spintronics, laying a foundation for future developments in quantum computing and spintronic devices.

Chirality refers to the property of objects whose mirror images cannot be perfectly superimposed, much like the relationship between a person's left and right hands. Chirality is omnipresent in nature, from molecules to materials, and chiral structures often exhibit unique optical, electronic, and chemical properties. For example, the biological activity of many drug molecules differs significantly based on their chirality. In materials science, the development of chiral materials is crucial for advancing frontier technologies such as optical devices, spintronics, and quantum computing.

Researchers from ICN2, ICMAB-CSIC and the Bulgarian Academy of Science have shown how the interaction with palladium diselenide (PdSe₂) can modify and enhance graphene’s spintronic performance. The team's finding improve existing understanding of spin dynamics in graphene-based van der Waals heterostructures and could be key for developing more efficient computing devices.

Van der Waals heterostructures are materials formed by combining layers of different ultra-thin materials stacked on top of each other. In recent years, these structures have proven to be very useful for studying and understanding unusual physical phenomena, making them promising candidates for the development of new technologies. The new study analyzed the interactions that occur in a graphene and palladium diselenide (PdSe₂) heterostructure. The team stresses: "Our results showed that PdSe₂ can induce significant changes in the spin transport properties and dynamics of graphene, providing new possibilities for controlling information-carrying spin currents”. These findings constitute an important step forward in elucidating spin physics in van der Waals heterostructures and could allow for spin-logic devices in the future.

Researchers from the National University of Singapore (NUS), working with teams from University of California, Kyoto University and others, have reported a breakthrough in the development of next-generation graphene-based quantum materials, opening new horizons for advancements in quantum electronics.

The innovation involves a novel type of graphene nanoribbon (GNR) named Janus GNR (JGNR). The material has a unique zigzag edge, with a special ferromagnetic edge state located on one of the edges. This unique design enables the realization of one-dimensional ferromagnetic spin chain, which could have important applications in quantum electronics and quantum computing.

Researchers from Korea have designed a new MRAM structure, based on graphene, that offers higher efficiency (and lower heat generation) compared to existing MRAM solutions. The design of the MRAM device is based on a graphene layer sandwiched between a magnetic insulator (yttrium iron garnet) and a ferroelectric material (PVDF-TrFE). Upon application of a voltage pulse, the current flow through the graphene is altered, enabling the storage of binary data based on this current direction.

The recent study demonstrates non-volatile control of spin-charge conversion at room temperature in graphene-based heterostructures through Fermi level tuning. The team used a polymeric ferroelectric film to induce non-volatile charging in graphene. To demonstrate the switching of spin-to-charge conversion, the scientists performed ferromagnetic resonance and inverse Edelstein effect experiments. 

A team of researchers from CIC nanoGUNE, IKERBASQUE, IMEC and CNRS have reported a spintronic device that leverages proximity effects alone, specifically a 2D graphene-based spin valve. The functioning of this valve relies only on the proximity to the van der Waals magnet Cr₂Ge₂Te₆. Spin precession measurements showed that the graphene acquires both spin–orbit coupling and magnetic exchange coupling when interfaced with the Cr₂Ge₂Te₆. This leads to spin generation by both electrical spin injection and the spin Hall effect, while retaining spin transport. The simultaneous presence of spin–orbit coupling and magnetic exchange coupling also leads to a sizeable anomalous Hall effect.

The primary objective of this recent study was to tackle a long-standing research challenge, namely that of realizing the first-ever seamless 2D spintronic device. The spin valve they developed could enable the manipulation and transport of spin entirely in the 2D plane.

A Spanish-German collaboration recently studied graphene-cobalt-iridium heterostructures at BESSY II. The results show how two desired quantum-physical effects reinforce each other in these heterostructures, which could lead to new spintronic devices based on these materials.

Spintronics uses the spins of electrons to perform logic operations or store information. Ideally, spintronic devices could operate faster and more energy-efficiently than conventional semiconductor devices. However, it is still difficult to create and manipulate spin textures in materials. Graphene, a 2D honeycomb structure made of carbon atoms, is considered an interesting candidate for spintronic applications. Graphene is typically deposited on a thin film of heavy metal. At the interface between graphene and heavy metal, a strong spin-orbit coupling develops, which gives rise to different quantum effects, including a spin-orbit splitting of energy levels (Rashba effect) and a canting in the alignment of spins (Dzyaloshinskii-Moriya interaction). The spin canting effect is especially needed to stabilize vortex-like spin textures, known as skyrmions, which are particularly suitable for spintronics.

Researchers at CIC nanoGUNE BRTA, Charles University in Prague and IKERBASQUE have designed a new complex material with unique properties that could be beneficial for spintronics.

Twist engineering has emerged as a fascinating approach for modulating electronic properties in van der Waals heterostructures. While theoretical works have predicted the modulation of spin texture in graphene-based heterostructures by twist angle, experimental studies are lacking. In this recent work, by performing spin precession experiments, the team demonstrates tunability of the spin texture and associated spin–charge interconversion with twist angle in WSe₂/graphene heterostructures.

Researchers at the University of Wyoming, Pennsylvania State University, Northeastern University, The University of Texas at Austin, Colorado State University and Japan's National Institute for Materials Science have developed a method to control tiny magnetic states within ultrathin, two-dimensional van der Waals magnets - a process similar to how flipping a light switch controls a bulb.

The team developed a device known as a magnetic tunnel junction, which uses chromium triiodide - a 2D insulating magnet only a few atoms thick - sandwiched between two layers of graphene. By sending a tiny electric current called a tunneling current through this sandwich, the direction of the magnet's orientation of the magnetic domains (around 100 nanometers in size) can be dictated within the individual chromium triiodide layers.