Topological insulators

An international team of researchers has succeeded in understanding, for the first time, how the topological properties of multilayer systems of Tungsten di-telluride (WTe₂) can be changed systematically by means of scanning tunneling microscopy.

WTe₂ has been found to be a promising material for the realization of topological states, which are regarded as the key to novel spintronics devices and quantum computers of the future due to their unique electronic properties. 

University of Tokyo researchers have created a material that confines electrons in one dimension in the form of a special bismuth-based crystal known as a high-order topological insulator.

To create spintronic devices, new materials need to be designed that take advantage of quantum behaviors not seen in everyday life. For spintronic applications, a new kind of electronic material is required - a topological insulator. It differs from other materials by insulating throughout its bulk, but conducting only along its surface. And what it conducts is not the flow of electrons themselves, but a property of them known as their spin or angular momentum.

Researchers from the Tokyo Institute of Technology (Tokyo Tech) developed a new MRAM cell structure that relies on unidirectional spin Hall magnetoresistance (USMR). The new cell structure is reportedly very simple with only two layers which could lead to lower-cost MRAM devices.

The spin Hall effect leads to the accumulation of electrons with a certain spin on the lateral sides of a material. By combining a topological insulator with a ferromagnetic semiconductor, the researchers managed to create a device with giant USMR.

Researchers from two FLEET universities in Australia, RMIT and UNSW, collaborated in a theoretical–experimental project that discovered a previously unseen mode of giant magneto-resistance (GMR) in 2D Fe₃GeTe₂ (FGT). This surprising result suggests a different underlying physical mechanisms in vdW hetero-structures.

The research shows that vdW materials (2D material) could offer higher functionaly cmopared to traditional spintronic approaches.

Researchers from Europe developed heterostructures built from graphene and topological insulators and have shown the strong tunability and suppression of the spin signal and spin lifetime in these structures.

Associate Professor Saroj Prasad Dash from Chalmers University of Technology explains that the advantage of using heterostructures built from two Dirac materials is tha graphene in proximity with topological insulators still supports spin transport, and concurrently acquires a strong spin–orbit coupling.

Researchers from the University of Minnesota have managed to deposit Bismuth Selenide (Bi₂Se₃) films using a simple sputtering technique.

Bismuth Selenide is topological insulator and a promising material for spintronics applications including MRAM devices. The material produced in this research featured a high spin torque at room temperatures.

Researchers from the Tokyo Institute of Technology have developed a new thin film material made from bismuth-antimony (BiSb) that is a topological insulator that simultaneously achieves a colossal spin Hall effect and high electrical conductivity.

This material could be used as the basis of spin-orbit torque MRAM (SOT-MRAM). SOT-MRAM SOT-MRAM can overcome the limitation of spin-transfer torque in MRAM memories - and provide a much faster, denser and much more efficient memory technology. Up until now, though, no suitable material that features both high electrical conductivity and a high spin hall effect was developed.

Researchers from Singapore's NUS and the University of Missouri developed a new all-electric method to measure the spin texture of topological insulators. The researchers say that this method could lead to an easier (and cheaper) methods of developing spintronics devices.

The new work revealed a close relation between the spin texture of topological surface states (TSS) and a new kind of magneto-resistance. The researchers observed the second order nonlinear magneto-resistance in a prototypical 3D TI Bi₂Se₃ films, and showed that it is sensitive to TSS. In contrast with conventional magneto-resistances, this new magneto-resistance shows a linear dependence on both the applied electric and magnetic fields.

Researchers from NUS have demonstrated for the first time room temperature magnetization switching driven by giant spin-orbit torques (SOT) in topological insulator/conventional ferromagnetic heterostructures with an extremely low current density.

The researchers believe that such switching that uses so little power could be used to scale up spintronics devices. The researchers achieved the switching using an 8-nm layer of Bi₂Se₃ grown on top of a 6 nm layer of NiFe, a widely used ferromagnet.

Researcherrs from Likoping University in Sweden demonstrated a method to generate and manipulate the surface spin current in topological insulators.

The researchers used a combination of a topological insulator (Bismuth Telluride, Bi2Te3) and a regular GaAs semiconductor. The electrons were generated with the same spin in the GaAs using polarized light. The electrons were then transferred to the TI.