Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

High-temperature superconductivity in atomically thin films

03.06.2015

A route to developing ultimate superconducting nano-devices

A research group at Tohoku University has succeeded in fabricating an atomically thin, high-temperature superconductor film with a superconducting transition temperature (Tc) of up to 60 K (-213°C). The team, led by Prof. Takashi Takahashi (WPI-AIMR) and Asst. Prof. Kosuke Nakayama (Dept. of Physics), also established the method to control/tune the Tc.


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

This finding not only provides an ideal platform for investigating the mechanism of superconductivity in the two-dimensional system, but also paves the way for the development of next-generation nano-scale superconducting devices.

The research results were published in Nature Materials on June 1, 2015.

Superconductors are regarded as one of the most promising candidates for next-generation advanced electronic devices, because the unique quantum effects in superconductors are a great advantage in achieving the energy-saving and ultrahigh-speed processing.

However, the device application of superconductors has long been hindered. The largest obstacle is the necessity of a huge and expensive cooling system with liquid helium, because of the low Tc of conventional superconductors, which is close to absolute zero (0 K, - 273 °C)*1. It has also been a big challenge to realize the high-density integration of superconductors into electronic devices. In order to overcome these problems, it is definitely necessary to develop a new superconductor with higher- Tc, that can be fabricated into a thin film.

The research team at Tohoku University turned its attention to iron selenide (FeSe), which is a member of iron-based superconductors*2. While 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.

The researchers at first fabricated high-quality, atomically thin FeSe films [Fig. 1], with thickness of between one monolayer (which corresponds to three-atoms thickness) and twenty monolayers (sixty-atoms thickness), by using the molecular-beam-epitaxy (MBE) method*3. Then they carefully investigated the electronic structure of grown films by angle-resolved photoemission spectroscopy (ARPES)*4 [Fig. 2].

In the ARPES measurement, the researchers observed the opening of a superconducting gap at low temperature*5, 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.

While multilayer films do not show superconductivity in the as-grown state, the researchers have discovered a novel method to deposit alkali atoms onto the films and thereby control the electron density in the film. By employing this method, the researchers have succeeded in converting non-superconducting multilayer FeSe films into high-Tc superconductors with Tc as high as ~50 K.

The present result gives a great impact to both the basic and applied researches in superconductors. The researchers have clearly shown how the superconductivity is emerged, enhanced and controlled in atomically thin FeSe films. While the Tc achieved in this study (50-60 K) is still lower than that of the cuprate high-Tc superconductors (highest Tc?135 K) which caused the "high-Tc fever" in the world 30 years ago, it obviously exceeds the record of other "high-Tc superconductors" such as fullerene (C60) superconductors (Tc~33 K) and MgB2 (Tc~39K), closely approaching the temperature of liquid nitrogen (77 K).

The present report would lead to intensive researches to further increase Tc by changing the number of atomic layers, the amount of doped electrons and the species of substrate. The present result would also widen the range of both basic and applied researches on superconductivity, because the Tc of 50-60 K achieved in the present study is high enough to keep the superconducting state by using a closed-cycle-gas-type cooling system without liquid helium.

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. The ultrathin high-Tc superconductor would effectively contribute to the significant down-sizing and consequent high-density integration in electric circuits, leading to the realization of future-generation electronic devices with high energy-saving and ultrahigh-speed operation.

This work was supported by grants from the Japan Society for the Promotion of Science (JSPS) and Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT).

###

Manuscript information:

Research team: Y. Miyata, K. Nakayama, K. Sugawara, T. Sato and T. Takahashi
Title: "High-temperature Superconductivity in Potassium-coated Multilayer FeSe Thin Films"
Publication: Nature Materials
Publication Date: June 1, 2015

Terms

*1) K (Kelvin)
A unit of temperature based on the absolute scale. The following relation converts this scale to the scale of degree Celsius (°C). °C = K - 273.15

*2) Iron-based superconductors
A group of superconductors consisting of two-dimensional iron layer, which was first discovered in 2008 by Prof. Hideo Hosono at Tokyo Institute of Technology, Japan.

*3) Molecular-beam-epitaxy method
A method of growing a thin, singlecrystal film on a substrate. Constituent atoms are selectively evaporated and deposited on a substrate under vacuum in a well-controlled manner. This method has an advantage in growing a high-quality single crystal film.

*4) Angle-resolved photoemission spectroscopy
An experimental technique to directly determine the energy and momentum of electrons in solids. It is based on the external photoelectric effect predicted by Einstein. Recent significant improvement of the energy resolution enables the precise investigation of superconducting electrons.

*5) Superconducting gap
An energy cost to create a superconducting electron pair (Cooper pair). The magnitude is directly observed by angle-resolved photoemission spectroscopy.

Contact Information:

Takashi Takahashi
WPI Research Center,
Advanced Institute for Materials Research (WPI-AIMR), Tohoku University
E-mail: t.takahashi@arpes.phys.tohoku.ac.jp
Tel: +81-22-795-6417

Kosuke Nakayama
Department of Physics, Tohoku University
E-mail: k.nakayama@arpes.phys.tohoku.ac.jp
Tel: +81-22-795-6477

For enquiries about WPI-AIMR:
E-mail: outreach@wpi-aimr.tohoku.ac.jp
Tel: +81-22-217-6146

Takashi Takahashi | EurekAlert!

More articles from Materials Sciences:

nachricht Move over, Superman! NIST method sees through concrete to detect early-stage corrosion
27.04.2017 | National Institute of Standards and Technology (NIST)

nachricht Control of molecular motion by metal-plated 3-D printed plastic pieces
27.04.2017 | Ecole Polytechnique Fédérale de Lausanne

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

From volcano's slope, NASA instrument looks sky high and to the future

27.04.2017 | Earth Sciences

Control of molecular motion by metal-plated 3-D printed plastic pieces

27.04.2017 | Materials Sciences

Move over, Superman! NIST method sees through concrete to detect early-stage corrosion

27.04.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>