An atomically thin, high-temperature superconductor film has been created, by a research group at Tohoku University, which has a superconducting transition temperature (Tc) of up to 60 K (-213°C).
Superconductors are looked at as being among the most promising technologies for next-generation advanced electronic devices. This is because the special quantum effects in superconductors are a big advantage in getting ultrahigh-speed processing and energy savings.
The group’s finding provides a perfect platform for investigating the mechanism of superconductivity in two-dimensional systems. It also opens a door to the development of next-generation nano-scale superconducting devices.
In order to overcome the problems inherent in the device application of superconductors, namely achieving high-density integration of superconductors into electronic devices, not to mention the necessity of a huge and expensive cooling system utilizing liquid helium, due to the low Tc of conventional superconductors, the research team at Tohoku University turned its attention to iron selenide.
The team, led by Prof. Takashi Takahashi and Asst. Prof. Kosuke Nakayama, chose iron selenide (FeSe) since although the Tc of bulk FeSe is only 8 K (-265 °C), a signature of higher-Tc superconductivity has been suggested in ultrathin film and its verification has been urgently required.
Initially, the researchers fabricated high-quality, atomically thin FeSe films, with thicknesses of between one monolayer (which corresponds to three-atoms thickness) and twenty monolayers (sixty-atoms thickness). They used the molecular-beam-epitaxy (MBE) method.
Next, they carefully investigated the electronic structure of grown films by angle-resolved photoemission spectroscopy (ARPES).
ARPES measurement revealed the opening of a superconducting gap at low temperatures, which is direct evidence of the emergence of superconductivity in the films. The researchers found that the Tc estimated from the gap-closing in a monolayer film is surprisingly high (above 60 K), which is about 8 times higher than the Tc of bulk FeSe.
An ultrathin high-Tc superconductor would contribute to a meaningful down-sizing and resulting high-density integration in electric circuits, leading to the realization of future-generation electronic devices with high energy-saving and ultrahigh-speed operation.
The present success in fabricating an atomically thin high-temperature superconductor not only provides an ideal platform to investigate the novel two-dimensional superconductivity, but also opens a route to developing an ultimate superconducting nano-device consisting of atomic-size electronic parts.
Y. Miyata, K. Nakayama, K. Sugawara, T. Sato & T. Takahashi. High-temperature superconductivity in potassium-coated multilayer FeSe thin films Nature Materials (2015) doi:10.1038/nmat4302
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