Message from the Director

Research theme 1

FLEET’s Research Theme 1 is developing the concept of a topological transistor for low-energy electronics. In 2021 a UOW-Monash-UNSW team demonstrated that a particular topological transistor concept called the topological quantum field-effect transistor (TQFET) can beat ‘Boltzmann’s tyranny’ and switch at voltages lower than the limit set by room-temperature thermodynamics in a conventional transistor. The concept has been developed further by FLEET researchers at Monash, RMIT, UOW and UNSW who have proposed that the TQFET can be integrated with ferroelectric materials with effective negative capacitance to create a negative-capacitance TQFET (NC-TQFET). The team benchmarked the NC-TQFET theoretically against conventional silicon devices, demonstrating that it could use eight times less energy than a similar-sized silicon counterpart.

FLEET Theme 1 researchers continue to improve understanding of novel 2D topological materials. In 2021, FLEET researchers at RMIT and UNSW measured the magnetic quantisation axis and directly demonstrated topological spin-momentum locking in the edge states of 2D topological insulator WTe₂, a critical property for dissipationless transport of current along the edges of a 2D topological insulator.

Topological insulator electronics devices now feature as a promising ‘beyond CMOS’ technology in the 2020 IEEE International Roadmap for Devices and Systems, and in 2021 FLEET contributed updated information for the 2022 edition of this important industry roadmap.

Research theme 2

FLEET’s Research Theme 2 aims to use dissipationless flow in exciton or exciton-polariton superfluids for low-energy devices. FLEET’s team are now world leaders in the race to exploit dissipationless phenomena in 2D van der Waals semiconductors for room-temperature applications. In 2021, the team was the first in the world to demonstrate room-temperature dissipationless transport of exciton-polaritons in monolayer semiconductor WS₂. The team is also exploiting the unique properties of the half-light half-matter exciton-polaritons to create new kinds of topological states. Spatial patterning of light creates patterns that change not only the energy of the exciton-polaritons, but also their rate of creation and annihilation, allowing new ‘non-Hermitian’ topological states, which are difficult to achieve in other systems.

Theme 2 researchers have also directly visualised the existence of biexcitons (bound pairs of excitons) in monolayer semiconductors using coherent ultra-fast spectroscopy. The Theme 2 theory team continues to make advances in understanding interacting polariton systems, including how polaritons interact with each other and with free charge carriers, and how quantum correlations arise in confined polaritons.

Research theme 3

FLEET’s Research Theme 3 aims to use light to control superfluidity and topology, creating new paradigms for low-energy devices. In 2021, Theme 3 researchers at Swinburne University of Technology observed the dynamics of an ultra-cold atomic cloud that has suddenly been switched from a normal gas to a dissipationless superfluid state. Theme 3 researchers developed a comprehensive theory of vortex dynamics and pinning in superfluid flows. In related work, FLEET researchers have also observed for the first time the fluid-like flow of (non-superfluid) electrons in channels of a conventional semiconductor with very low disorder.

In the process of using ultra-fast light to modify the properties of 2D semiconductors, Theme 3 researchers at Swinburne and Monash found that they could use machine learning to disentangle the complex information in the optical spectra of 2D materials, allowing them to better understand how doping, strain and disorder in solid state materials affect their optical properties.