New Fermi arcs could provide a new path for electronics

Date:
March 24, 2022
Source:
DOE/Ames Laboratory
Summary:
Newly discovered Fermi arcs that can be controlled through magnetism
could be the future of electronics based on electron spins. During
a recent investigation of the rare-earth monopnictide NdBi
(neodymium- bismuth), researchers discovered a new type of Fermi
arc that appeared at low temperatures when the material became
antiferromagnetic, i.e., neighboring spins point in opposite
directions.



FULL STORY ========================================================================== Newly discovered Fermi arcs that can be controlled through magnetism
could be the future of electronics based on electron spins. These new
Fermi arcs were discovered by a team of researchers from Ames Laboratory
and Iowa State University, as well as collaborators from the United
States, Germany, and the United Kingdom. During their investigation of
the rare-earth monopnictide NdBi (neodymium-bismuth), the research team discovered a new type of Fermi arc that appeared at low temperatures when
the material became antiferromagnetic, i.e., neighboring spins point in opposite directions.


========================================================================== Fermi surfaces in metals are a boundary between energy states that are
occupied and unoccupied by electrons. Fermi surfaces are normally closed contours forming shapes such as spheres, ovoids, etc. Electrons at the
Fermi surface control many properties of materials such as electrical
and thermal conductivity, optical properties, etc. In extremely rare
occasions, the Fermi surface contains disconnected segments that are
known as Fermi arcs and often are associated with exotic states like superconductivity.

Adam Kaminski, leader of the research team, explained that newly
discovered Fermi arcs are the result of electron band splitting, which
results from the magnetic order of Nd atoms that make up 50% of the
sample. However, the electron splitting that the team observed in NdBi
was not typical band splitting behavior.

There are two established types of band splitting, Zeeman and Rashba. In
both cases the bands retain their original shape after splitting. The
band splitting that the research team observed resulted in two bands
of different shapes. As the temperature of the sample decreased, the
separation between these bands increased and the band shapes changed, indicating a change in fermion mass.

"This splitting is very, very unusual, because not only is the separation between those bands increasing, but they also change the curvature,"
Kaminski said. "This is very different from anything else that people
have observed to date." The previously known cases of Fermi arcs in Weyl semimetals persist because they are caused by the crystal structure of
the material which is difficult to control. However, the Fermi arcs
that the team discovered in NdBi are induced by magnetic ordering
of the Nd atoms in the sample. This order can be readily changed by
applying a magnetic field, and possibly by changing the Nd ion for
another rare earth ion such as Cerium, Praseodymium, or Samarium (Ce,
Pr, or Sm). Since Ames Lab is a world leader in rare earth research,
such changes in composition can be easily explored.



========================================================================== "This new type of Fermi arcs appears whenever the sample becomes antiferromagnetic. So when the sample develops magnetic order, these
arcs just appear seemingly out of nowhere," said Kaminski.

According to Kaminski, another important characteristic of these new Fermi
arcs is that they have what is called spin texture. In normal metals,
each electronic state is occupied by two electrons, one with a spin up,
one with a spin down, so there is no net spin. The newly discovered Fermi
arcs have single orientation of spin at each of their points. Since they
exist only in a magnetically ordered state, the arcs can be switched on
and off very quickly by applying a magnetic pulse, for example from an ultrafast laser.

"Having such a spin decoration or spin texture is important because
one of the quests in electronics is to move away from the charge-based electronics.

Everything that you use now is based on moving electrons in wires and
that causes dissipation," Kaminski said.

The ability to control the spin of electrons relates to a new branch of information technology called spintronics, which is based on electron
spin rather than on moving charges along wires.

"Instead of moving a charge, we either flip the orientation of the
spin or cause the propagation of the spin along the wire," Kaminski
explained. "These spin changes technically should not dissipate energy,
so it doesn't cost a lot of energy to store information as spin or to
move information as spin." Kaminski emphasized the importance of this
finding to the field, but he said there is still a lot of work to be
done before these findings can be used in new technology.

Crystal growth and characterization were supported by Center for the Advancement of Topological Semimetals (CATS), an Energy Frontier Research Center funded by the U.S. DOE, Office of Basic Energy Sciences.


========================================================================== Story Source: Materials provided by DOE/Ames_Laboratory. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Benjamin Schrunk, Yevhen Kushnirenko, Brinda Kuthanazhi, Junyeong
Ahn,
Lin-Lin Wang, Evan O'Leary, Kyungchan Lee, Andrew Eaton,
Alexander Fedorov, Rui Lou, Vladimir Voroshnin, Oliver J. Clark,
Jamie Sa'nchez- Barriga, Sergey L. Bud'ko, Robert-Jan Slager,
Paul C. Canfield, Adam Kaminski. Emergence of Fermi arcs due to
magnetic splitting in an antiferromagnet. Nature, 2022; 603 (7902):
610 DOI: 10.1038/s41586-022- 04412-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220324184641.htm

--- up 3 weeks, 3 days, 10 hours, 51 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)