Massless particle discovery could radically accelerate electronics

An exotic particle theorized more than 85 years ago has finally been discovered. Dubbed the "Weyl fermion", it is a strange but stable particle that has no mass, behaves as both matter and anti-matter inside a crystal, and is claimed to be able to create completely massless electrons. Scientists believe that this new particle may result in super-fast electronics and significant inroads into novel areas of quantum computing.

There aretwo types of particles that make up the universe and everything in it: fermionsand bosons. In simple terms, fermions are all the particles that make up matter(for example, electrons), and bosons are all the particles that carry force(for example, photons). Ordinarily, fermions such as electrons can collide witheach other, losing energy, and no two fermions can share the same state at the sameposition at the same time. Weyl fermions being massless, however, have no suchrestrictions.

Weyl fermions were firstmooted in 1929 by physicist and mathematician Hermann Weyl, who theorized thatmassless fermions able to carry an electric charge could exist. Without mass,he believed, electrons created from Weyl fermions would be able to moveelectric charge in a circuit much more quickly than ordinary electrons. Infact, according to this latest research, electric current carried by Weyl electronsin a test medium is able to move at least twice as fast as that carried byelectrons in graphene and at least 1,000 times faster than in ordinarysemiconductors.

The international team led by Princeton University scientists used the PrincetonInstitute for the Science and Technology of Materials (PRISM) andLaboratory for Topological Quantum Matter and Spectroscopy to look into manydozens of crystal arrangements before alighting upon the asymmetrical tantalumarsenide crystal (a semi-metalthat has the properties of both a conductor and an insulator) asa prime candidate in the hunt for the theorized particle.

Over-sized crystals of the tantalum arsenide were firstplaced in a scanning tunneling spectromicroscope cooled to near absolute zero todetermine if they matched the hypothetical specifications for accommodatinga Weyl fermion. Then, once the crystals had passed that test, the team took themto the Lawrence Berkeley National Laboratory in California where high-energy photonbeams fired from a particle accelerator were shone through them. This testfinally confirmed the presence of the existence of the long sought after Weylfermion.

"Thenature of this research and how it emerged is really different and moreexciting than most of other work we have done before," said Su-Yang Xu, apostdoctoral research associate at Princeton. "Usually, theorists tell usthat some compound might show some new or interesting properties, then we asexperimentalists grow that sample and perform experiments to test theprediction. In this case, we came up with the theoretical prediction ourselvesand then performed the experiments. This makes the final success even moreexciting and satisfying than before."

As a quasiparticle – that is, a particle that exists inside a solid (inthis instance) but acts as if it were a weakly interacting particle in freespace – the Weyl fermion is massless and has a high degree ofmobility. This is because, as the particle's spin is both in the same direction as itsmotion (known in physics as "right-handed") and in the opposite direction in which it moves ("left-handed"), it is able to traversethrough and around obstacles that impede ordinary electrons.

"It'slike they have their own GPS and steer themselves without scattering,"said Princeton University physicist Zahid Hasan, who lead the research team."They will move and move only in one direction since they areeither right-handed or left-handed and never come to an end because they justtunnel through. These are very fast electrons that behavelike unidirectional light beams and can be used for new types of quantumcomputing."

Weyl originally posited hisfermion as part of an alternate model to the theory of relativity proposed byhis associate Albert Einstein. And, though Weyl's hypothesis lost out toEinstein’s, the idea of his theoretical particle continuedto tantalize physicists for many years afterward. However, as a merely "theoretical" particle, even when inklings of the Weyl fermion were uncovered over the decades, they were mistakenly thought to be evidence of neutrinos. In hindsight, the evidence was actually for Weyl fermions, for in 1998 neutrinos were actually discovered to have a small amount of mass.

"People figured that although Weyl's theory was not applicable torelativity or neutrinos, it is the most basic form of fermion and had all otherkinds of weird and beautiful properties that could be useful," said Hasan."After more than 80 years, we found that this fermion was already there,waiting. It is the most basic building block of all electrons. It is excitingthat we could finally make it come out following Weyl's 1929 theoreticalrecipe."

The team included researchers from Princeton's Department of Physics, Peking University, the National Taiwan University, the National University of Singapore, Oak Ridge National Laboratory; and Northeastern University.

The results of this work were recently published in the journal Science.

Source: Princeton University