Three types of atomically thin metal films grown on silicon, including STM imaging. Left: SCI Pb/Si(111). Centre: √7 × √3 Pb/Si(111). Right: √7 × √3 In/Si(111)
An international FLEET collaboration publishing a review of atomically-thin ‘high temperature’ superconductors finds that each has a common driving mechanism: interfaces.
The team, including researchers from the University of Wollongong, Monash University and Tsinghua University (Beijing), found that interfaces between materials were the key to superconductivity in all systems examined.
The enhancement of superconductivity at interfaces (interface superconductivity enhancement effect) in atomically-thin superconductors is a unique tool for discovering new high-temperature superconductors, and could be used to finally unlock the elusive mechanism behind high-temperature superconductivity.
β-FeSe lattice structure. a) 3D model. b) Top view.
Systems studied include:
- elemental metals grown on semiconductors
- single-layer iron-based superconductors
- atomically-thin cuprate (copper based) superconductors
The review investigated the role of molecular-beam epitaxy (MBE), scanning tunnelling spectroscopy (STM/STS), scanning transmission electron microscopy (STEM), physical properties measurement system (PPMS), in fabricating and identifying atomically-thin superconductors.
Superconductors: a background
Atomically-thin superconductors (whether iron based or copper based) are a type of ‘high temperature’ (Type II or unconventional) superconductor in that they have a transition temperature (Tc) much higher than a few degrees Kelvin above absolute zero.
The driving force behind such Type II superconductors has remained elusive since their discovery in the 1980s. Unlike ‘conventional’ superconductors, it is clear they cannot be directly understood from the BCS (Bardeen, Cooper, and Schrieffer) electron-phonon coupling theory.
Superconductivity in single-layer FeSe films grown on STO substrates. Top: STM image, bottom: scanning tunneling spectroscopy showing superconducting gap with pronounced coherence peaks
In successive discoveries the transition temperature Tc has been driven steadily higher, and in the last decade there has been significant advances in the use of atomically-thin superconductors, both iron- and copper-based.
These new discoveries challenge current theories regarding the superconducting mechanism of unconventional superconductors and indicate promising new directions for realising high-Tc superconductors.
“The ultimate goal of the research of superconductivity is finding superconductors with a superconducting transition temperature (Tc) at or higher than room temperature,” says lead author Dr Zhi Li (University of Wollongong).
Timeline
- 1911 superconductivity discovered in Hg, Tc =4.2 K
- other elemental metals confirmed superconductors Tc< 10 K
- 1957 microscopic (Bardeen, Cooper &Schrieffer/ BCS) theory of superconductivity with electron-phonon coupling as driving force
- 1986 ‘surprising’ superconductivity of La-based cuprate (‘high temperature’ superconductors), Tc >30 K
- 2007 superconductivity in iron-based compound LaFeAsO, Tc 26 K
- 2008 iron-based superconductivity, Tc 55 K
- 2012 high-temperature interface superconductivity in single-layer FeSe films on SrTiO3
- ???? room-temperature superconductivity
The study
STM imaging (enlargements on right). Top: anatase TiO2 (001) island on SrTiO3(001) substrate. Bottom: SUC / DUC FeSe films on anatase TiO2.
The review paper Atomically thin superconductors was published in the journal Small in May 2020 (DOI 10.1002/smll.201904788).
The authors acknowledge support from the Australian Research Council’s support via the Centre of Excellence, Discovery and Future Fellowship programs.
The review investigated the role of molecular-beam epitaxy (MBE), scanning tunnelling spectroscopy (STM/STS), scanning transmission electron microscopy (STEM), physical properties measurement system (PPMS), in fabricating and identifying atomically-thin superconductors.
Collaborating FLEET personnel
- Scientific AI Dr Zhi Li, UOW
- PhD student Lina Sang, UOW
- Research Fellow Dr Peng Liu, UOW
- Research Fellow Dr Zengji Yue, UOW
- CI Prof Michael Fuhrer, Monash University
- PI Prof Qikun Xue, Tsinghua University
- CI Prof Xiaolin Wang, UOW
Novel materials study at FLEET
The properties of novel, atomically-thin materials are studied at FLEET, an Australian Research Council Centre of Excellence, within the Centre’s Enabling technology A.
The Centre for Future Low-Energy Electronics Technologies (FLEET) is a collaboration of over a hundred researchers, seeking to develop ultra-low energy electronics to face the challenge of energy use in computation, which already consumes 8% of global electricity, and is doubling each decade.
Each of FLEET’s three research themes are heavily enabled by these novel materials, including 2D topological materials (Research Theme 1), atomically thin semiconductors (as hosts for excitons in Research Theme 2, and for realising non-equilibrium topological phenomena in Research Theme 3).
More information
- Contact Dr Zhi Li zhili@uow.edu.au
- Contact Prof Xiaolin Wang xiaolin@uow.edu.au
- Read more atomically-thin materials news at FLEET
