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).
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
*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.
WPI Research Center,
Advanced Institute for Materials Research (WPI-AIMR), Tohoku University
Department of Physics, Tohoku University
For enquiries about WPI-AIMR:
Takashi Takahashi | EurekAlert!
Osaka university researchers make the slipperiest surfaces adhesive
18.10.2017 | Osaka University
Think laterally to sidestep production problems
17.10.2017 | King Abdullah University of Science & Technology (KAUST)
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
18.10.2017 | Materials Sciences
18.10.2017 | Physics and Astronomy
18.10.2017 | Physics and Astronomy