DATE2023.02.16 #Press Releases
This rare metal could produce large spin current
Computer simulations reveal a tungsten structure with a large spin current which may improve computer memory and quantum information transmission
February 16, 2023
Flowing electrons carry two properties: electric charge and spin. The spin of an electron is a fundamental magnetic property that takes only one value—spin-up or spin-down—like a compass needle. In the spin-up state, the electron rotates clockwise; in the spin-down state, it rotates counterclockwise. While flowing electric charge leads to the electric current that runs in your devices, flowing electron spins lead to the spin current, which is faster and energy efficient. But not all materials produce the spin current, and its magnitude depends on the crystal structure of the material. A rare metal, tungsten with a cubic crystal structure, is currently one of the best-known spin-current-producing materials. Using computer simulations, Takahiro Ishikawa and his team discovered two new orthorhombic tungsten structures with a much better spin current. The finding has implications for improving computer memory and quantum information transmission.
“Determination of crystal structures needs a huge amount of work because a crystal structure has many degrees of freedom, for example, atomic positions, lattice lengths, and lattice angles,” Ishikawa said. “In this study, we explored stable crystal structures of tungsten using a computational algorithm inspired by Charles Darwin’s theory on the evolution of species, called evolutionary algorithms.” Evolutionary algorithms help discover optimal solutions to a given problem.
The team explored the potential candidates for crystal structures of tungsten using evolutionary algorithms and by calculating the electronic states of materials based on quantum mechanics. As a result of the simulation, they found 15 metastable structures. Of the 15 structures, two orthorhombic crystal structures stood out as materials with a further enhanced spin current than the cubic crystal structure of tungsten.
Image 1: Orthorhombic tungsten predicted by an evolutionary algorithm. Eight atoms form a unit.
Image 2: Another orthorhombic tungsten predicted by an evolutionary algorithm. Here, sixteen atoms form a unit.
The two orthorhombic tungsten structures with an enhanced spin current are theoretical. Experimentally synthesizing the orthorhombic tungsten would open many applications of this material in quantum computing. “The recent deposition technology of thin film enables us to create artificial materials by stacking atomic layers, one layer at a time,” Ishikawa said. "So, we hope that we can succeed in synthesizing orthorhombic tungsten film for the applications.”
The spin-based electronics or spintronics would revolutionize quantum computing. Finding the best material for spin current is just the beginning of future ultrafast information transfer and robust memory storage technologies.
Ishikawa and his team believe this study could inspire the exploration of new materials producing the large spin current using evolutionary algorithms.
Journal Physical Review Materials Title Large intrinsic spin Hall conductivity in orthorhombic tungstenAuthorTakahiro Ishikawa, Ryosuke Akashi, Kotaro Kubo, Yuta Toga, Koji Inukai, Itti Rittaporn, Masamitsu Hayashi, and Shinji TsuneyukiDOI