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 Smallest transistor worldwide switches current with a single atom in solid electrolyte
17.08.2018 | Karlsruher Institut für Technologie (KIT)

nachricht Protecting the power grid: Advanced plasma switch for more efficient transmission
17.08.2018 | DOE/Princeton Plasma Physics Laboratory

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: Color effects from transparent 3D-printed nanostructures

New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference

Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...

Im Focus: Unraveling the nature of 'whistlers' from space in the lab

A new study sheds light on how ultralow frequency radio waves and plasmas interact

Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

Im Focus: The “TRiC” to folding actin

Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.

Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

LaserForum 2018 deals with 3D production of components

17.08.2018 | Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

 
Latest News

Smallest transistor worldwide switches current with a single atom in solid electrolyte

17.08.2018 | Physics and Astronomy

Robots as Tools and Partners in Rehabilitation

17.08.2018 | Information Technology

Climate Impact Research in Hannover: Small Plants against Large Waves

17.08.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>