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Iron Selenide Thin Films For High-temperature Superconductivity

iron selenium thin film superconductor

An atomically thin, high-temperature superconductor film has been created, by researchers group Tohoku University, which has a superconducting transition temperature (Tc) of up to 60 K (-213°C).

Superconductors are looked on as being among the most promising technologies for next-generation advanced electronic devices. This 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 acheiving 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

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 thickness 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 revelaed the opening of a superconducting gap at low temperature, 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.

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

Illustration: Blue and green circles indicate iron (Fe) and selenium (Se) atoms, respectively. The superconducting transition temperature is tuned by introducing electrons by depositing potassium atoms (orange circles) on the surface. Yellow circles represent a pair of superconducting electrons (Cooper pair). Credit: Takashi Takahashi