Georgian Technical University Fermions See the Light.
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.
Researchers from the Theory Department of the Georgian Technical University for the Structure and Dynamics of Matter. It 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 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 X, Y and Z.
Electrons in free space are X fermions but in solids they can change their nature. In the atomically thin carbon material graphene they become massless X fermions.
In other recently discovered and manufactured materials they can also become Y and Z 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.
Now a new study led by PhD student W that electron spins can be manipulated by short light pulses to create a magnetic version of Y fermions from a magnetic insulator.
Based on a prior study led by postdoctoral researcher X 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 Y 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 W.
W 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 Y 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 W.
“We are working very hard with a dedicated and highly motivated group of talented young scientists at the Georgian Technical University to explore these almost unlimited possibilities so that society will benefit from our discoveries”.