Sep 16, 2020 | |
Reviewing the quantum anomalous Hall effect(Nanowerk News) A collaboration across three FLEET nodes has reviewed the fundamental theories underpinning the quantum anomalous Hall effect (Small, "Quantum Anomalous Hall Effect in Magnetic Doped Topological Insulators and Ferromagnetic Spin-Gapless Semiconductors – A Perspective Review"). |
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The quantum anomalous Hall effect (QAHE) is one of the most fascinating and important recent discoveries in condensed-matter physics. | |
It is key to the function of emerging ‘quantum’ materials, which offer potential for ultra-low energy electronics. | |
QAHE causes the flow of zero-resistance electrical current along the edges of a material. | |
QAHE in topological materials: key to low-energy electronics |
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Topological insulators, recognised by the Nobel Prize in Physics in 2016, are based on a quantum effect known as the quantum anomalous Hall effect. | |
“Topological insulators conduct electricity only along their edges, where one-way ‘edge paths’ conducts electrons without the scattering that causes dissipation and heat in conventional materials,” explains lead author Muhammad Nadeem. | |
QAHE was first proposed by 2016 Nobel-recipient Prof Duncan Haldane (Manchester) in the 1980s, but it subsequently proved challenging to realize QAHE in real materials. Magnetic-doped topological insulators and spin-gapless semiconductors are the two best candidates for QAHE. | |
The quantum Hall effect (QHE) is a quantum-mechanical version of the Hall effect, in which a small voltage difference is created perpendicular to a current flow by an applied magnetic field. | |
The quantum Hall effect is observed in 2D systems at low temperatures within very strong magnetic fields, in which the Hall resistance undergoes quantum transitions — ie, it varies in discrete steps rather than smoothly. | |
QAHE describes an ‘unexpected’ (ie, ‘anomalous’) quantisation of the transverse ‘Hall’ resistance, accompanied by a considerable drop in longitudinal resistance. | |
QAHE is referred to as ‘anomalous’ because it occurs in the absence of any applied magnetic field, with the driving force instead provided by either a) spin-orbit coupling or b) intrinsic magnetization. | |
Researchers seek to enhance these two driving factors in order to strengthen QAHE, allowing for topological electronics that would be viable for room-temperature operation. | |
It’s an area of great interest for technologists,” explains Xiaolin Wang. “They are interested in using this significant reduction in resistance to significantly reduce the power consumption in electronic devices.” | |
“We hope this study will shed light on the fundamental theoretical perspectives of quantum anomalous Hall materials,” says co-author Prof Michael Fuhrer (Monash University), who is Director of FLEET. | |
The study |
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The collaborative, theoretical study concentrates on these two mechanisms: 1)large spin-orbit coupling (interaction between electrons’ movement and their spin); and 2) strong intrinsic magnetization (ferromagnetism). | |
Four models were reviewed that could enhance these two effects, and thus enhance QAHE, allowing topological insulators and spin fully-polarized zero-gap materials (spin gapless semiconductors) to function at higher temperatures. | |
“Among the various candidate materials for QAHE, spin-gapless semiconductors could be of potential interest for future topological electronics/spintronics applications”, explains Muhammad Nadeem. |
Source: ARC Centre of Excellence in Future Low-Energy Electronics Technologies (FLEET) | |
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