Thin Films Become Superconductive At Higher Temperatures

This thin, iron-based film conducts electricity at 35°C above absolute zero without the need for doping.

AsianScientist (May 9, 2016) – Researchers in Japan have found that a thin film transitions to a superconducting state at a temperature far above absolute zero—a potential boon for the field of superconductivity. Their findings were published in Proceedings of the National Academy of Sciences.

Superconductivity is the phenomenon by which some materials, when cooled to a certain temperature, exhibit the unusual property of allowing an electrical current to flow through unimpeded, without the application of any additional power. This type of current expels magnetic fields from within superconductors; a useful property harnessed via the use of superconducting magnets in numerous areas such as computing, medical equipment and particle accelerators.

However, one challenge is the need for cooling with liquid helium, which is both difficult and expensive to produce and use. High-temperature superconductivity is important because it overcomes many of the difficulties associated with having to maintain conditions very close to absolute zero.

Recently, Tokyo Institute of Technology (Tokyo Tech) researchers showed that a thin film comprising of the elements iron and selenium (FeSe) can be induced to switch from an insulator-like state, where it resists the flow of electricity, to one where electricity flows through it freely at a much higher than normal temperature.

They also managed to reveal the mechanism by which this occurs: the accumulation of electrons at an extremely high density on the film’s surface. The high temperature at which this transition occurs, -238°C, or 35°C above absolute zero, widens the range of possible experiments and applications in superconductivity.

Furthermore, the researchers show that an iron selenide film approximately ten nm thick transitions from an electrical insulator-like state to a superconducting one at a temperature of 35 K—more than fourfold the equivalent temperature for the same type of film with a thickness of 110 nm.

“We used an electric double-layer transistor with a gate voltage of 5.5 V applied to thin epitaxial films of FeSe to induce a superconductive state,” said co-author Dr. Hidenori Hiramatsu.

“We found that electrons had accumulated at a very high level in the FeSe channel, which caused the high-temperature transition to superconductivity.”

“The fact that thin FeSe changes from an insulator to a superconductor at 35 K means we can now examine the induction of superconduction without having to perform doping with impurities, which can degrade the structure of the material and carrier transport,” lead author Dr. Kota Hanzawa explains.

“We should now be able to determine the absolute highest temperature at which transitions to superconductivity can occur. This can benefit research and applications across our field.”

The team plans to build on its findings in high-temperature superconductivity to develop more real-world applications utilizing the remarkable properties of superconducting materials.


The article can be found at: Hanzawa et al. (2016) Electric Field-Induced Superconducting Transition of Insulating FeSe Thin Film at 35 K.

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Source: Tokyo Institute of Technology.
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