Researchers explore elusive high-energy particles in a crystal

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Physicists at MIT found a new phenomenon in an unconventional metal could provide a new way of making highly sensitive detectors for mid-infrared elusive wavelengths.

Physicists said, all the fundamental particles in nature into two categories, fermions and bosons. The fermions have three types: Dirac, Majorana, and Weyl.

Weyl fermion

The Weyl fermion existence is posited as part of the equations that form the widely accepted Standard Model of subatomic physics, Weyl fermions have never actually been observed experimentally.

The theory predicts that they should move at the speed of light, and at the same time spin about the direction of motion. They come in two varieties depending on whether their rotation around the direction of motion is clockwise or counterclockwise. This property is known as the handedness or chirality of Weyl fermions.

In a study, an MIT team was able to measure Weyl fermion chirality by using circularly polarized light.

Gedik, an associate professor in the Department of Physics, says, the researchers found that a metal called tantalum arsenide (TaAs), exhibits an interesting optoelectronic property called the circular photogalvanic effect.

The TaAs can produce an electrical current without applying external voltages. Moreover, the direction of the current is dictated by the chirality of Weyl fermions and can be switched by changing the light polarization from left-handed to right-handed.

The amount of current generated in this way turns out to be surprisingly large 10 to 100 times stronger than the response of other materials used for detecting this kind of light. This could make the material useful for extremely sensitive light detectors in this mid-infrared part of the spectrum.

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Despite being predicted a long time ago, Weyl fermions have never been observed as a fundamental particle in particle physics.

But, the new experiments have shown that in these unconventional metals, ordinary electrons can behave in a strange way so that their motion mimics the behavior of Weyl fermions, and can exhibit a range of novel properties.

Electrons can behave like Weyl fermions in those metals. They always come in pairs that always have opposite chirality.

By measuring the current using electrodes attached to the material for different light polarizations, they were able to deduce the chirality of Weyl fermions responsible for this current.

More information: [Nature physics]

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