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.
Higher-Tc Superconductivity
Electrons are emitted from the surface by shinning ultraviolet light. The electronic structure of crystal is determined by measuring the energy and the emission angle of electrons.
Credit: Takashi Takahashi
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.
Reference:
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
