Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Electron "Pairing": Triplet superconductivity proven experientially for first time

01.12.2010
Tracking down Cooper pairs: RUB researchers confirm theoretical hypothesis

Researchers at Ruhr-Universität Bochum (RUB), Christian-Albrechts-Universität zu Kiel (CAU) and Santa Barbara (USA) have made the first experimental breakthrough in quantum physics: Their studies on the "pairing behavior" of electrons have proven for the first time the existence of electron pairs, so-called Cooper pairs, with parallel spin direction. Cooper pairs cause superconductivity – this is a particular state of material, in which the electrical resistance disappears. Until now the existence of triplet Cooper pairs has only been predicted theoretically.

The results achieved by this research team headed by Prof. Kurt Westerholt and Prof. Hartmut Zabel (Department of Physics and Astronomy at RUB) could contribute to new, power saving components in the future. The researchers reported on their findings in the American Physical Society's noted journal "The Physical Review“.

Electron pairs in singlet state

If it were possible to eliminate electrical resistance we could reduce our electric bill significantly and make a significant contribution to solving the energy problem, if it were not for a few other problems. Many metals as well as oxides demonstrate a superconductive state, however only at low temperatures. The superconductive effect results from Cooper pairs that migrate through the metal together "without resistance". The electrons in each Cooper pair are arranged so that their composite angular momentum is zero. Each electron has an angular momentum, the so-called spin, with a value of 1/2. When one electron spins counterclockwise (-1/2) and the other clockwise (+1/2), the total of the two spin values is zero. This effect, found only in superconductors, is called the singlet state.

Superconductive Cooper pairs

If a superconductor is brought into contact with a ferromagnetic material, the Cooper pairs are broken up along the shortest path and the superconductor becomes a normal conductor. Cooper pairs cannot continue to exist in a singlet state in a ferromagnetic material. Researches at RUB (Prof. Konstantin Efetov, Solid State Physics) among others have, however, theoretically predicted a new type of Cooper pair, which has a better chance of survival in ferromagnetic materials. In such Cooper pairs the electrons spin in parallel with one another so that they have a finite spin with a value of 1. Since this angular momentum can have three orientations in space, it is also known as the triplet state. "Obviously there can also be only one certain, small fraction of Cooper pairs in a triplet state, which then quickly revert to the singlet state" explained Prof. Kurt Westerholt. "The challenge was to verify these triplet Cooper pairs experimentally“.

Tunnel current from Cooper pairs

Superconductors allow us to produce highly sensitive detectors for magnetic fields, which even allow detection of magnetic fields resulting from brain waves. These detectors are called SQUID's (superconducting quantum interference devices) – components which use the superconductive quantum properties. The central feature in these components consists of so-called tunnel barriers with a series of layers made up of a superconductor, insulator and another superconductor. Quantum mechanics allows a Cooper pair to be "tunneled" through a very thin insulating layer. Tunneling of a large number of Cooper pairs results in a tunnel current. "Naturally the barrier cannot be too thick, otherwise the tunnel current subsides. A thickness of one to two nanometers is ideal“, according to Prof. Hermann Kohlstedt (CAU).

Double success in Bochum und Kiel

If part of the tunnel barrier is replaced by a ferromagnetic layer, the Cooper pairs are broken up while they are still in the barrier and do not reach the superconductor on the other side. The tunnel current decreases drastically. "Triplet Cooper pairs can, however, be tunneled much better through such a ferromagnetic barrier", says Dirk Sprungmann, who was involved as Ph.D. student. If we are successful in converting a portion of the singlet Cooper pairs to triplet Cooper pairs, the tunnel current should be significantly stronger and be able to pass through a thicker ferromagnetic layer. This is precisely what the physicists in Bochum and Kiel tested. They allowed the Cooper pairs to pass through ferromagnetic barriers with thicknesses of up to 10 nanometers. With this attempt the physicists achieved a double success. On the one hand they were able to experimentally verify the existence of triplet Cooper pairs, and, on the other, they demonstrated that the tunnel current is greater than for singlet Cooper pairs in conventional tunnel contacts. "These new ferromagnetic tunnel barriers may possibly be used for new types of components", states Dr. Martin Weides (Santa Barbara). With their research findings the scientists confirmed, among other things, the theoretical work of a Norwegian research team published only a few weeks before.

Title picture

D. Sprungmann, K. Westerholt, H. Zabel, M. Weides, H. Kohlstedt: Evidence of triplet superconductivity in Josephson junctions with barriers of the ferromagnetic Heusler alloy Cu2MnAl. Physical Review B 82 (2010), DOI: 10.1103/PhysRevB.82.060505

Further information

Prof. Hartmut Zabel, Prof. Kurt Westerholt, Experimental Physics IV – Solid State Physics, Department of Physics and Astronomy at RUB, Tel. +49 (0)234/32-23650, -23621, Email: hartmut.zabel@rub.de. Kurt.westerholt@rub.de

Prof. Dr. Hermann Kohlstedt, Nanoelektronik, Technische Fakultät Kiel, Christian-Albrechts-Universität Kiel, hko@tf.uni-kiel.de, +49 (0)431/880-6075

Editor: Jens Wylkop

Dr. Josef König | idw
Further information:
http://www.ruhr-uni-bochum.de/

More articles from Physics and Astronomy:

nachricht Igniting a solar flare in the corona with lower-atmosphere kindling
29.03.2017 | New Jersey Institute of Technology

nachricht NASA spacecraft investigate clues in radiation belts
28.03.2017 | NASA/Goddard Space Flight Center

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: A Challenging European Research Project to Develop New Tiny Microscopes

The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.

To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Researchers shoot for success with simulations of laser pulse-material interactions

29.03.2017 | Materials Sciences

Igniting a solar flare in the corona with lower-atmosphere kindling

29.03.2017 | Physics and Astronomy

As sea level rises, much of Honolulu and Waikiki vulnerable to groundwater inundation

29.03.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>