Case
Study
Reviewing the
quantum anomalous Hall effect (QAHE)
A FLEET collaboration in 2020 reviewed the quantum anomalous Hall effect (QAHE), one of the most fascinating and important recent discoveries in condensed-matter physics, and absolutely key to FLEET’s mission to develop ultra-low-energy electronics.
It is QAHE that allows the zero-resistance electrical ‘edge paths’ in topological insulators and other quantum materials.
“Topological insulators conduct electricity only along their edges, where one-way ‘edge paths’ conduct electrons without the scattering that causes dissipation and heat in conventional materials,” explains the review’s lead author, FLEET PhD student Muhammad Nadeem (University of Wollongong).
Nadeem led the team of FLEET researchers from UNSW, Monash University and UOW who reviewed the fundamental theories underpinning QAHE, and applications.
Demonstration of a material exhibiting QAHE, with the electrons going in opposite ways on opposite edges.
QAHE was first proposed by 2016 Nobel Prize recipient Prof Duncan Haldane (Princeton University) in the 1980s, although it subsequently proved challenging to realise QAHE in real materials. Magnetic-doped topological insulators and spin-gapless semiconductors are the two best candidates for QAHE.
QAHE describes an ‘unexpected’ (i.e. ‘anomalous’) quantisation of the transverse ‘Hall’ resistance, accompanied by a considerable drop in longitudinal resistance.
The driving force for this effect is provided by either spin-orbit coupling or intrinsic magnetisation.
Atomically-thin materials research at FLEET connects teams across the participating nodes. FLEET Research Fellow Dr Feixiang Xiang (UNSW) is shown visiting the labs at the University of Wollongong, with CI Prof Xiaolin Wang (UOW).
Researchers seek to enhance these two driving factors in order to strengthen QAHE and make topological electronics viable for room-temperature operation.
“It’s an area of great interest for technologists,” explains Prof Xiaolin Wang (UOW). “They are interested in using this significant reduction in resistance to reduce the power consumption in electronic devices.”
Four models were reviewed that could enhance these two effects and thus enhance QAHE, allowing topological insulators and spin fully-polarised, zero-gap materials (spin-gapless semiconductors) to function at higher temperatures.
Header image: Atomically-thin materials research at FLEET connects teams across the participating nodes. FLEET Research Fellow Dr Feixiang Xiang (UNSW) is shown visiting the labs at the University of Wollongong, with CI Prof Xiaolin Wang (UOW)
This research relates to FLEET milestones 1.15. See page 13 of Strategic Plan
The study was published in Small in September 2020 (see Publications)
Topological insulators conduct electricity only along their edges, where one-way ‘edge paths’ conduct electrons without the scattering that causes dissipation and heat in conventional materials.
Lead author, FLEET PhD student
Muhammad Nadeem (UOW)
Did you know...
The Quantum anomalous Hall effect was first succesfully demonstrated in the lab by FLEET PI Prof Qi-kun Xue (Tsinghua), in 2013.
Chief Investigator
Prof Xiaolin Wang
University of Wollongong
Directing Enabling technology A, Xiaolin investigates charge and spin effects in magnetic topological insulators, and leads synthesis of FLEET’s single-crystal bulk and thin-film samples.
Collaborating FLEET Personnel:
PhD Student
Muhammad Nadeem University of Wollongong
Chief Investigator
Alex Hamilton UNSW
Chief Investigator
Michael Fuhrer Monash University