Current generated when light hits a material reveals electrons behaving like an elusive particle

Scientists predicted and directly measured electrons in a semimetal. The electrons were behaving like elusive massless particles. Shining a circularly polarized light beam (pink spiral) onto a tantalum-arsenide semimetal (ball-and-stick crystal model) generates an electrical current (green arrow). Remarkably, the direction of the current flow changes by switching the light’s polarization from right-handed to left-handed, proving the handedness of exotic Weyl fermions. Credit: Massachusetts Institute of Technology

A massless particle, a.k.a. Weyl fermion, predicted nearly 100 years ago, has been found in another corner of physics. Electrons in a semimetal can behave like these particles. They are either right-handed or left-handed—they are mirror images like our hands. Theory predicted that Weyl semimetals could produce handedness-dependent electrical current by shining circularly polarized infrared light onto it. Scientists then confirmed and measured this current. Changing from right- to left-handed light switched the direction of the current, meaning they could determine the handedness of these electrons.

The detection of handedness of electrons in a Weyl semimetal opens new experimental possibilities for studying and controlling these elusive massless particles and their quantum weirdness. Their quantum behavior can lead to novel optical phenomena. One example is photocurrents (electrical current induced by light). Another example is the detection of photons (quantized packets of light) from the mid-infrared optical spectrum to lower frequencies (terahertz). Infrared detection is vital for night vision and heat imaging. Terahertz detection is useful for package-penetrating devices. In addition, the right- and left-handedness in a semimetal could be used like zeroes and ones in conventional computing. The result? Novel pathways to store and carry data.

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