Quantum materials breakthrough for energy-efficient data processing

Data centres, cloud services, AI and connected systems account for a rapidly growing share of global energy consumption. In the quest for new, more energy-efficient technological solution, spin electronics, or spintronics, has proven to be a new and promising approach. Instead of relying solely on the movement of electric charge, spintronics use magnetic states to carry information. More specifically, it takes advantage of a quantum property of electrons known as spin, which makes electrons behave like tiny magnets.

“Just like a compass needle, an electron’s spin can point in one of two directions – up or down. These two directions can be used to represent digital information, in the same way today’s electronics use 0s and 1s,” explains Saroj Dash, Professor of Quantum Device Physics at Chalmers University of Technology. 

Because spintronics is based on magnetism – which is a stable state – and does not depend on continuous charge currents, spintronics could enable faster and more energy-efficient electronics with reduced heat losses.

Unprecedented control of electron spin

Despite its promise, a number of challenges still remain before spintronics can benefit society on a broad scale. A key issue is achieving sufficient control over the spin of electrons – that is, their magnetic direction. So far, strong electrical currents or external magnetic fields have been required to control spin orientation with high precision, which undermines the intended energy savings. This is partly because it has been difficult to induce these magnetic states in existing materials, and partly because our understanding of quantum spin phenomena is still limited.

Researchers at Chalmers have now taken an important step forward. By stacking two quantum materials on top of each other, they have found a way to control electron spin with unparalleled precision – without relying on external magnetic fields or strong electrical currents.

“The combination of these two quantum materials enables us to control electron spin using only very small electrical currents. It also works at room temperature, which means the method could eventually make data-processing and memory technologies both faster and more energy-efficient,” says Saroj Dash, lead author of a study published in Nature Communications. 

Broken symmetry part of the solution

This method of carefully stacking atomically thin layers of different quantum materials is known in physics as van der Waals heterostructures. In the Chalmers researchers’ solution, they combine a material whose magnetism is oriented perpendicular to the surface with another material whose electrons have unusual properties. Together, they give rise to an entirely new and unexplored magnetic dynamics. Using weak electrical currents, the researchers can then steer the direction of magnetism so that the electrons’ spin switch in the desired way. The effect can partly be explained by the asymmetry that characterises the structure of one of the quantum materials used.

“Perfect symmetry can actually limit what a material can do. By deliberately breaking this symmetry, we were able to unlock new spin effects that simply aren’t possible in perfectly symmetric systems – and that gave us a completely different level of control over the direction of the electrons,” says Lalit Pandey, researcher in Quantum Device Physics at Chalmers and first author of the study. 

A “perfect bridge” enabled strong coupling and high control

A crucial part of the breakthrough is the interface between the two materials, which is perfectly smooth and therefore creates an ideal connection without “friction” or defects. This allows spin information to be transferred between the materials without being weakened or disturbed.

“You can think of it as a completely clean bridge between two materials,” says Saroj Dash. “This atomically thin and perfectly flat interface means the spin signal remains fully intact as it moves between the materials,” Saroj explains.

“What makes this particularly exciting is that the coupling is both strong and controllable,” says Lalit Pandey.

Opening the door to spintronics in practice

The results from Chalmers pave the way for a new and promising platform for developing spin-based electronics that are energy-efficient, tunable and don’t require external magnetic fields. Because the effect works at room temperature and can be achieved in relatively simple devices, the chances of integrating the technology into future electronics are increasing.

“This gives us a new design principle – rather than just searching for new materials, we can build entirely new properties through how we combine materials and break symmetries. This is a clear step towards next-generation spintronics, where we can control spin far more efficiently than before through smart quantum-material design,” says Saroj Dash.

More information about the study:
The scientific article Tunable unconventional spin orbit torque magnetization dynamics in van der Waals heterostructures has been published in Nature Communications.
The fabrication of devices was performed at Nanofabrication laboratory MyFab at Chalmers University of Technology.

Funding: 
The research project has received funding from Wallenberg Initiative Materials Science for Sustainability (WISE) funded by the Knut and Alice Wallenberg Foundation, European Comission (EU) Graphene Flagship, European Innovation Council (EIC) project 2DSPIN-TECH, 2D TECH VINNOVA competence center, , Swedish Research Council (VR), FLAG-ERA project 2DSOTECH and MagicTune, Carl Tryggers foundation, Graphene Center, Chalmers-Max IV collaboration grant, VR Sweden-India collaboration grant, Areas of Advance (AoA) Nano, AoA Materials Science and AoA Energy programs at Chalmers University of Technology.