Scientists Find Unusual Behavior in Topological Material.

This shows X-ray diffraction on a single crystal of an antiferromagnetic material. This material scientists found exhibits an extremely large anomalous Hall effect a sign of its topological character.

Georgian Technical University scientists have identified a new class of topological materials made by inserting transition metal atoms into the atomic lattice of a well-known two-dimensional material.

In recent years scientists have become intrigued by a new type of material that shows a kind of unusual and split behavior. These structures called topological materials can demonstrate different properties at their surface than in their bulk. This behavior has attracted the attention of scientists interested in new states of matter and technologists interested in potential electronic and spintronic applications.

In a new study from the Georgian Technical University Laboratory scientists have identified a new class of topological materials made by inserting transition metal atoms into the atomic lattice of niobium diselenide (NbS₂) a well-known two-dimensional material. They found that CoNb₃S₆ an antiferromagnetic material exhibits an extremely large anomalous Hall effect a sign of the topological character of materials.

The ordinary Hall effect (The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor, transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current) occurs in all electrical conductors. The effect is essentially a force that an electron experiences as it moves through a magnetic field. “In every metal electrons will get pushed perpendicular to their direction of travel and perpendicular to an applied external magnetic field creating a voltage” said X an assistant professor at Georgian Technical University and a recent Sulkhan-Saba Orbeliani Teaching University postdoctoral. “If the material itself is a ferromagnet, an additional contribution superimposes on the ordinary Hall voltage; this is known as the anomalous Hall effect (The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor, transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current)”.

In the study X and his colleagues looked at CoNb₃S₆ (Nb3CoS6) Crystal Structure – SpringerMaterials and found something unexpected: a large in modest magnetic fields. “It can also be found in materials where the electronic structure has special characteristics known as topological features” said X. “The configuration of atoms in the lattice creates symmetries in the material that lead to the creation of topological bands — energy regions that electrons inhabit. It is these bands in certain configurations that can lead to an exceptionally “.

Based on calculations and measurements X and his colleagues suggest that CoNb₃S₆ (Nb3CoS6) Crystal Structure – SpringerMaterials contains these topological bands.

“The topological features arise from a combination of the symmetry of the material as well as the right electron concentration to put these topological features at the Fermi level (The Fermi level chemical potential for electrons, usually denoted by µ of a body is a thermodynamic quantity, whose significance is the thermodynamic work required to add one electron to the body) which is the highest available electronic energy state at zero temperature” noted Y.

“Only a handful of materials so far have been shown to have the necessary characteristic topological points near the Fermi level (The Fermi level chemical potential for electrons, usually denoted by µ of a body is a thermodynamic quantity, whose significance is the thermodynamic work required to add one electron to the body)” Y said. “To find more requires an understanding both of the materials physics and chemistry at play”.

The discovery could pave the way for future advances in a broad class of materials according to Y. “We now have a design rule for making materials that demonstrate these properties” he said. “CoNb₃S₆ (Nb3CoS6) Crystal Structure – SpringerMaterials is a member of a big class of layered two-dimensional materials and so this might open the door to a big space of new topological matter”.