Shedding light on Weyl fermions

A wave of laser light hits the magnetic material, shaking the electron spins (arrows). This weakens magnetism and induces Weyl fermions in the laser-shaken material. Jörg Harms, MPSD

All known elementary particles can be sorted into two categories: bosons and fermions. Bosons carry forces, like the magnetic force or gravity, while fermions are the matter particles, like electrons. Theoretically it was predicted that fermions themselves can come in three species, named after the physicists Dirac, Weyl, and Majorana.

Electrons in free space are Dirac fermions, but in solids they can change their nature. In the atomically thin carbon material graphene they become massless Dirac fermions. In other recently discovered and manufactured materials, they can also become Weyl and Majorana fermions, which makes such materials interesting for future technologies such as topological quantum computers and other novel electronic devices.

In combination with a wave of bosons, namely photons in a laser, fermions can be transformed from one type to another, as proposed by MPSD theorists in 2016 (see ref. 1) below). Now a new study led by PhD student Gabriel Topp in the Emmy Noether group of Michael Sentef suggests that electron spins can be manipulated by short light pulses to create a magnetic version of Weyl fermions from a magnetic insulator.

Based on a prior study led by MPSD postdoctoral researcher Nicolas Tancogne-Déjean and Theory Director Angel Rubio (see ref. 2 below), the scientists used the idea of laser-controlled electron-electron repulsion to suppress magnetism in a pyrochlore iridate material where electron spins are positioned on a lattice of tetrahedra.

On this lattice, electron spins, like little compass needles, point all-in to the center of the tetrahedron and all-out in the neighboring one. This all-in, all-out combination together with the length of the compass needles leads to insulating behavior in the material without light stimulation.

However, modern computer simulations on large computing clusters revealed that, when a short light pulse hits the material, the needles start to rotate in such a way that, on average, they look like shorter needles with less strong magnetic ordering. Done in just the right way, this reduction of magnetism leads to the material becoming semi-metallic with Weyl fermions emerging as the new carriers of electricity in it.

„This is a really nice step forward in learning how light can manipulate materials on ultrashort time scales,“ says Michael Sentef. And Gabriel Topp adds: „We were surprised by the fact that even a too strong laser pulse that should lead to a complete suppression of magnetism and a standard metal without Weyl fermions could lead to a Weyl state.

This is because on very short time scales the material does not have enough time to find a thermal equilibrium. When everything is shaking back and forth, it takes some time until the extra energy from the laser pulse is distributed evenly among all the particles in the material.“

The scientists are optimistic that their work will stimulate more theoretical and experimental work along these lines. „We are just at the beginning of learning to understand the many beautiful ways in which light and matter can combine to yield fantastic effects and we do not even know what they might be today,“ says Angel Rubio. „We are working very hard with a dedicated and highly motivated group of talented young scientists at the MPSD to explore these almost unlimited possibilities so that society will benefit from our discoveries.“

1) “Creating stable Floquet-Weyl semimetals by laser-driving of 3D Dirac materials” – https://www.nature.com/articles/ncomms13940

2) “Ultrafast modification of Hubbard U in a strongly correlated material: ab initio high-harmonic generation in NiO” – https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.097402

Dr Michael Sentef: +49 (0)40 8998-88350

http://www.nature.com/articles/s41467-018-06991-8

http://MPSD press release: http://www.mpsd.mpg.de/506762/2018-10-weyl-sentef

Media Contact

Jenny Witt Max-Planck-Institut für Struktur und Dynamik der Materie

All news from this category: Physics and Astronomy

This area deals with the fundamental laws and building blocks of nature and how they interact, the properties and the behavior of matter, and research into space and time and their structures.

innovations-report provides in-depth reports and articles on subjects such as astrophysics, laser technologies, nuclear, quantum, particle and solid-state physics, nanotechnologies, planetary research and findings (Mars, Venus) and developments related to the Hubble Telescope.

Back to the Homepage

Comments (0)

Write comment

Latest posts

Seawater as an electrical cable !?

Wireless power transfers in the ocean For drones that can be stationed underwater for the adoption of ICT in mariculture. Associate professor Masaya Tamura, Kousuke Murai (who has completed the…

Rare quadruple-helix DNA found in living human cells with glowing probes

New probes allow scientists to see four-stranded DNA interacting with molecules inside living human cells, unravelling its role in cellular processes. DNA usually forms the classic double helix shape of…

A rift in the retina may help repair the optic nerve

In experiments in mouse tissues and human cells, Johns Hopkins Medicine researchers say they have found that removing a membrane that lines the back of the eye may improve the…

Partners & Sponsors

By continuing to use the site, you agree to the use of cookies. more information

The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. If you continue to use this website without changing your cookie settings or you click "Accept" below then you are consenting to this.

Close