This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Energy can be carried in a number of ways: by electrons, the particles that underpin all modern electronics, as well as by quasiparticles, the results of different particles interacting with one another at the quantum level. Columbia chemist Milan Delor has been watching these different forms of energy flow with an instrument called stroboSCAT, a unique microscope that uses strobe-like light pulses to capture particles and quasiparticles as they move through different materials.
The latest iteration of stroboSCAT, described in Nature Materials, can now resolve individual quantum energy carriers as they move through materials for the first time. It can also observe their interactions with greater precision than existing imaging techniques. Electrons can easily be tracked using transport measurements that record electrical resistance.
But such techniques cannot directly capture quasiparticles, like charge-neutral excitons or spin excitations. Delor first developed stroboSCAT as a postdoc working with Naomi Ginsberg at the University of California, Berkeley, in 2019. Over the years, he and his lab at Columbia have increased its temporal resolution to femtoseconds and its spatial resolution to just a few nanometers, and deployed it to detect electrons, excitons, phonons, magnons, ferrons, photons, polaritons and polarons in a variety of semiconductors and metals. stroboSCAT has yielded powerful insights into the transport properties of a wide range of materials, but only at high carrier densities.
Imagine dropping ink into water, Delor explained. How the droplet diffuses can reveal important details about the medium, but only up to a point. Eventually, the individual ink particles become too spread out to see anything meaningful.
"That's always been the catch," he said. "To take single-particle measurements, you need to start with a low density of carriers, but, as they move, they become lost in the noise of the measurements." A few years ago, a team of researchers from the University of Würzburg and the University of Ottawa published a technique for distinguishing single quantum particles by performing spectroscopic measurements at varying laser intensities. "It's a beautiful paper, implemented in spectroscopy, but it doesn't capture spatial information.
We realized that our technique was extremely well suited to a similar simple tweak: cycling different intensities of light to create the excitations," Delor said. "It's an elegant solution to a major obstacle: We can now distinguish single quantum states from many as they move through real space." In the current Nature Materials paper, the team, led by Delor's graduate student Jack Tulyag (GSAS '26), demonstrated several powerful capabilities of their intensity-cycling stroboSCAT. Most significantly for Delor, they can now isolate single electrons moving through a 2D semiconductor.
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