Researchers from the Theory Department of the Max Planck Institute for Structure and Dynamics (MPSD) in Hamburg and North Carolina State University in the US have demonstrated that the long-sought magnetic Weyl semi-metallic state can be induced by ultrafast laser pulses in a three-dimensional class of magnetic materials dubbed pyrochlore iridates. Their results, which have now been published in Nature Communications, could enable high-speed magneto-optical topological switching devices for next-generation electronics.
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://MPSD press release: http://www.mpsd.mpg.de/506762/2018-10-weyl-sentef
Jenny Witt | Max-Planck-Institut für Struktur und Dynamik der Materie
Quantum gas turns supersolid
23.04.2019 | Universität Innsbruck
Explosion on Jupiter-sized star 10 times more powerful than ever seen on our sun
18.04.2019 | University of Warwick
The human eye is particularly sensitive to green, but less sensitive to blue and red. Chemists led by Hubert Huppertz at the University of Innsbruck have now developed a new red phosphor whose light is well perceived by the eye. This increases the light yield of white LEDs by around one sixth, which can significantly improve the energy efficiency of lighting systems.
Light emitting diodes or LEDs are only able to produce light of a certain colour. However, white light can be created using different colour mixing processes.
Researchers led by Francesca Ferlaino from the University of Innsbruck and the Austrian Academy of Sciences report in Physical Review X on the observation of supersolid behavior in dipolar quantum gases of erbium and dysprosium. In the dysprosium gas these properties are unprecedentedly long-lived. This sets the stage for future investigations into the nature of this exotic phase of matter.
Supersolidity is a paradoxical state where the matter is both crystallized and superfluid. Predicted 50 years ago, such a counter-intuitive phase, featuring...
A stellar flare 10 times more powerful than anything seen on our sun has burst from an ultracool star almost the same size as Jupiter
A localization phenomenon boosts the accuracy of solving quantum many-body problems with quantum computers which are otherwise challenging for conventional computers. This brings such digital quantum simulation within reach on quantum devices available today.
Quantum computers promise to solve certain computational problems exponentially faster than any classical machine. “A particularly promising application is the...
The technology could revolutionize how information travels through data centers and artificial intelligence networks
Engineers at the University of California, Berkeley have built a new photonic switch that can control the direction of light passing through optical fibers...
17.04.2019 | Event News
15.04.2019 | Event News
09.04.2019 | Event News
24.04.2019 | Life Sciences
24.04.2019 | Life Sciences
24.04.2019 | Life Sciences