New topology properties found in “old” Cobalt disulfide material

New topology buildings found in

Experimental testing of Weyl nodes in Cobalt disulfide, compared with the theoretical prediction. Credit: Princeton Department of Chemistry, Schoop Lab

Leading collaborations of institutions in the U.S. and abroad, the Princeton University Department of Chemistry reports on new topology properties of the magnetic pyrite Cobalt disulfide (CoS)2) which expands our understanding of electrical channels in this long-studied material.

Using an angle-adjusted photoelectron spectroscope and ab-initio calculations, researchers working with the Schoop Lab found that most CoS2 nodes contained Weyl nodes that allow them to predict surface properties aige. The material hosts Weyl-fermions and Fermi-arc surface states within its band structure, which may potentially serve as a platform for exotic onions and place it among material candidates for used in spintronic devices.

The inquiry also settles a long – running debate, confirming the presence of CoS2 it is not real semi-metal. Semi-metal is any material that acts as a conductor of electrons of one direction of spinning but as an insulator or semiconductor for those of the other side. Although all semi-metals are ferromagnetic, most ferromagnets are not semi-metals. This discovery that CoS2 not semi-metal has a significant impact on materials and mechanical engineering.

Leslie Schoop, associate professor of chemistry at Princeton Chemistry, called the work “rediscovering new physics in old material.” The research was published this week in Advances in science.

CoS2 It has been the subject of study for many decades because of its attractiveness, and since the early 2000s – before the prediction and discovery of topology predictors – because of its potential to be a semi-metal. . Researchers were “pleased” to adjourn this latter debate.

Through Schoop’s research, the material was found to be a rare example of that group of magnetic topology metals that have been proposed as agents for cost-to-spinning conversion. By removing the bulk electronic structure and surface of CoS2, researchers have demonstrated that there is a relationship between electrical channels in the inner material that can predict other states at its surface. In a material, an electric current can pass through the bulk or flow across the surface. The researchers found that CoS was a majority2 there are objects called Weyl nodes within its structure that are electronic channels that can predict other states at the surface.

“The beautiful physics here is that you have those Weyl nodes that want polarized surface states. These can be harvested for spintronic applications,” Schoop said.

“These lightning states that only exist at the surface with associated chirality, and because of that chirality the electricity can only move in certain directions,” she said. think about using these chiral states in other applications. There are very few magnetic materials where they have been found before. “

Isolation refers to that building which makes an object or system unrecognizable from its mirror image – ie immovable – and which is an important property in many branches of science.

Schoop said the electronic channels are polar. This magnetism could be used to manipulate the material: scientists could change the direction of magnetization and surface states could then reshape in response to this activated magnetic field.

Paper co-author Maia Vergniory, of the Donostia International Physics Center in Spain, said, “Very few magnetic materials have been measured to form such surface states, or Fermi arcs, and this is similar to the fourth, So, it’s amazing that we could measure and understand the spinchannels in material that has been known for so long. “

As colleagues in 2016, Schoop and Vergniory considered a study of the properties of CoS products2, especially whether it could be classified as pure semi-metal. They were inspected through several planes after Schoop arrived in Princeton in 2017, and graduate students worked on him under Schoop and under Vergniory at Donostia.

Niels Schröter, a collaborator at the Paul Scherrer Institute in Switzerland and lead author of the paper, oversaw the team at the Swiss Light Source that mapped the Weyl nodes material.

“What we wanted to measure was not just a surface electronic structure,” Schröter said. “We also wanted to learn something about the bulk electronic buildings, and to get both of these complementary pieces of information, we had to use the specialist ADRESS railway line at the Swiss Light Source to generate electricity. studied in depth in most of the material. “

Schröter explained how engineers could build a machine down the road using this material.

“You would put this material in contact with another material, for example with a magnetic suction device or something like that in which you then want to create magnetic waves by running an electric current through it.

“The beauty of these topology materials is that these interface electrodes that can be used for injection, they are very strong. You can’t get rid of them easily. This is where the meet the fields of topology and spintronics, because topology may be a way to ensure that you have those polarized interface states in contact with other magnetic materials that you want to control by currents or fields. “

Schoop said, “I find this kind of rediscovery in the very old and well – researched material very inspiring, and I’m delighted to have these two wonderful colleagues who have helped to ‘slows down. ”

Spin Hall effect in semimetal Weyl for energy efficient information technology

Further information:
“Weyl fermions, Fermi arcs, and small-spin carriers in ferromagnetic CoS2Advances in science (2020).… .1126 / sciadv.abd5000

Presented by Princeton University

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