An elusive hypothetical particle comesin imitation form.

Lurking within a solid crystal is aphenomenon that is mathematically similar to proposed subatomic particlescalled axions, physicist JohannesGooth and colleagues report online October 7 in Nature.

If axions exist as fundamentalparticles, they could constitute a hidden form of matter in the cosmos, darkmatter. Scientists know dark matter exists thanks to its gravitational pull,but they have yet to identify what it is. Axions are one possibility, but no one has found the particles yet (SN: 4/9/18).

Enter the imitators. The axions analogswithin the crystal are a type of quasiparticle, a disturbance in a material thatcan mimic fundamental particles like axions. Quasiparticles result from thecoordinated jostling of electrons within a solid material. Its a bit like how birdsin a flock seem to take on new forms by syncing up their movements.

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Axions were first proposed in thecontext of quantum chromodynamics the theory that explains the behaviors of quarks,tiny particles that are contained, for example, inside protons. Axions andtheir new doppelgngers are mathematically similar but physically totallyunrelated, says theoretical physicist Helen Quinn of SLAC National AcceleratorLaboratory in Menlo Park, Calif., one of the scientists who formulated thetheory behind axions. That means scientists are no closer to solving their darkmatter woes.

Still, the new study reveals for thefirst time that the phenomenon has a life beyond mere equations, inquasiparticle form. Its actually amazing, says Gooth, of the Max Planck Institutefor Chemical Physics of Solids in Dresden, Germany. The idea of axions is avery mathematical concept, in a sense, but it still exists in reality.

In the new study, the researchersstarted with a material that hosts a type of quasiparticle known as a Weyl fermion,which behaves as if massless (SN: 7/16/15).When the material is cooled, Weyl fermions become locked into place, forming acrystal. That results in the density of electrons varying in a regular patternacross the material, like a stationary wave of electric charge, with peaks inthe wave corresponding to more electrons and dips corresponding to fewerelectrons.

Applying parallel electric and magneticfields to the crystal caused the wave to slosh back and forth. That sloshing isthe mathematical equivalent of an axion, the researchers say.

To confirm that the sloshing wasoccurring, the team measured the electric current through the crystal. Thatcurrent grew quickly as the researchers ramped up the electric fields strength,in a way that is a fingerprint of axion quasiparticles.

If the scientists changed the directionof the magnetic field so that it no longer aligned with the electric field, theenhanced growth of the electric current was lost, indicating that the axionquasiparticles went away. This material behaves exactly as you would expect,Gooth says.

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Physicists have found quasiparticles that mimic hypothetical dark matter axions - Science News