Quantum materials could find uses in light-controlled electronic devices

“We showed… that not only is the polarization of optical excitation important, but one can control light-matter interaction in materials by spatial dispersion of light”Ritesh Agarwal

Researchers have demonstrated that electrical properties in quantum materials could be controlled by light, findings that could assist the development of photonic and spintronic materials that transfer digitized information based on the spin of photons or electrons. Weyl semimetals were shown to access unique quantum properties that could be used to develop light-controlled electronic devices, and also improve the observation of quantum phenomena through controlling specific quantum properties just by changing light beam patterns.

As described in Nature Materials [Ji et al. Nat. Mater (2019) DOI: 10.1038/s41563-019-0421-5], the team, from the University of Pennsylvania along with a colleague from Nanyang Technological University, showed that Weyl semimetals have bulk quantum states whose electrical properties can be controlled by light. In exploring how light interacts with complex materials to obtain insights about materials to help fabricate new photonic devices, the group were keen to examine the photocurrent response of such topological materials with interesting band structures.

In experiments on Weyl semimetals, instead of the electrical current flowing in a single direction it moved around the semimetal in a circular pattern. They produced a new framework to explain the effect, narrowing it down to a single theory related to the structure of the light beam.Instead of a beam of light being laterally uniform, these experiments were based on the beam having a boundary, and what made the current circulate involved its behavior at the edge of the beam.

With this framework, the unique circular movements of the electrical current could be ascertained, as well as how the current's direction could be controlled by altering the light beam's structure. As co-team leader Ritesh Agarwaltold Materials Today, “We showed… that not only is the polarization of optical excitation important, but one can control light-matter interaction in materials by spatial dispersion of light”.

The work brings an understanding of how carriers are excited in the Weyl semimetal system, as well as how they relax and produce the circulating photocurrent response. The photocurrents are sensitive to the nature of spatial dispersion of optical excitation and polarization, which is key to producing future optical detectors that are sensitive to photon spin and gradients of optical field, something not possible with conventional photodetectors.

The team now hopes to fabricate photodetectors with sensitivity to photon spin, the intensity gradient of the optical beam and also perhaps the orbital angular momentum modes of the light beam that interacts with the material. The study could also be extended to include other optical beam patterns for new quantum computing materials that allow more information to be encoded onto a single photon of light.