Physicists in Germany have led experiments that show the inertia of electrons can form ‘tornadoes’ inside a quantum semimetal.
It’s almost impossible for electrons to sit still, and their motions can take on some bizarre forms. Case in point: an analysis of electron behavior in a quantum material called tantalum arsenide reveals vortices.
But the story gets weirder. These electrons aren’t spiraling in a physical place – they’re doing so in a quantum blur of possibility called momentum space. Rather than drawing a map of a particles’ potential locations, or position space, momentum space describes their motion through their energy and direction.
Similar vortices have previously been observed in position space. Measuring values of the electrons’ momenta and plotting them out on a three-dimensional graph, a striking vortex pattern emerges there as well.
The discovery could help pave the way for a completely new form of electronics: a field called ‘orbitronics‘ that could tap into the twisting power of electrons instead of their electrical charge to carry information in electronic circuits or quantum computers.
The discovery was made in an intriguing semimetal crystal called tantalum arsenide. In a way that’s not surprising – it was in this material that the long-predicted Weyl fermion was found for the first time. This massless particle essentially functions like a super-efficient electron, and its discovery required the special quantum properties of tantalum arsenide.
Those properties made the material the perfect choice for hunting quantum tornadoes. The problem arose in figuring out how to observe them.
Scientists at a research center called Complexity and Topology in Quantum Matter (ct.qmat) in Germany led a study that managed to pull it off using a technique called angle-resolved photoemission spectroscopy (ARPES) on a sample of tantalum arsenide.
“ARPES is a fundamental tool in experimental solid-state physics. It involves shining light on a material sample, extracting electrons, and measuring their energy and exit angle,” says Maximilian Ünzelmann, experimental physicist at the University of Würzburg.
“This gives us a direct look at a material’s electronic structure in momentum space. By cleverly adapting this method, we were able to measure orbital angular momentum.”
Each observation, however, only takes a two-dimensional snapshot of the electrons in the material. To confirm that quantum tornadoes form in this realm, the team had to stack each measurement up into a 3D model, like a CT scan. The end result is a colorful model that shows a very clear vortex structure.
“We analyzed the sample layer by layer, similar to how medical tomography works,” says Ünzelmann. “By stitching together individual images, we were able to reconstruct the three-dimensional structure of the orbital angular momentum and confirm that electrons form vortices in momentum space.”
The team says that further work could lead to not only more efficient electronics, but an entirely new class of devices called orbitronics. This could also work alongside another potential successor of electronic technology – spintronics, which encodes information in the spin of electrons.
The research was published in the journal Physical Review X.
