Scientists given the green light, to control microscopic electricity

Researchers based at the University of Cambridge have discovered a new phenomenon where light can be used to control electricity in disordered semiconductor materials on the nanoscale.

While a lot still remains to be discovered in the field, with this new tool, we are very excited to see what other sorts of new phenomena can emerge at the intersection of disorder and semiconductor physics! Arjun Ashoka

Disorder in semiconductors has traditionally been thought to harm a material's ideal performance. Now, scientists at the University of Cambridge’s Cavendish Laboratory have found that disorder can drive the phenomenon of spin domain formation on short timescales in an emerging class of easily processable semiconductor materials. They have discovered a new phenomenon where, when light is shined on a disordered material, tiny electrical currents form small magnetic pockets on very fast timescales. “Normally, to segregate electrons spatially based on their spin, we would need magnets, but with these special disordered materials, we can use light instead,” say Prof. Akshay Rao, who led the research team at the Cavendish Laboratory.

The scientists have developed a new kind of microscope that can image electronic currents on a 1000th of a billionth of a second and used it to study a kind of disordered material - halide perovskites. They did this by tailoring very short laser pulses through a lot of glass and a microscope objective to image electronic currents that behave as if they are tiny magnets.

The findings published in Nature Materials, show cases that when light was shone on disordered material, tiny regions with different spins (like tiny magnets) appeared very quickly - within 1000th of a billionth of a second. What’s even more interesting is that the direction of motion and the flow of electricity in these regions can be controlled using a property of light known as polarisation.

“We found, much to our surprise, that these local electronic currents spatially segregate themselves because of the kind of structural disorder present in these materials,” explains Arjun Ashoka, PhD student at the Cavendish Laboratory and the first author of the paper. “This happens as these tiny regions create special currents that are locked to their magnetic moments, leading to the segregation of these little magnets through simple local rules - if the little magnets point up, the electricity moves one way and if it points down, it moves the opposite way."

This discovery could open up new possibilities for making devices that use light to control electricity on very fast timescales and short lengthscales. Although in opposition to the current notion, scientists have managed to find a case for the argument that disorder in semiconductors can be useful. “While a lot still remains to be discovered in the field, with this new tool, we are very excited to see what other sorts of new phenomena can emerge at the intersection of disorder and semiconductor physics,” said Arjun Ashoka .

Reference: Ashoka, A., Nagane, S., Strkalj, N. et al. Local symmetry breaking drives picosecond spin domain formation in polycrystalline halide perovskite films. Nat. Mater. (2023). DOI:10.1038/s41563-023-01550-z

Image: Blue goes left, red goes right - local rules for electronic currents in disordered materials cause ultrafast spin domain formation

Image Credit: Arjun Ashoka