Featured Research

from universities, journals, and other organizations

New class of unconventional superconductors

Date:
July 3, 2012
Source:
University of Huddersfield
Summary:
Researchers have discovered a new class of exotic unconventional superconductors. When a superconductor is cooled below its 'critical temperature', the fluid of electrons, which is responsible for the conduction of electricity through the material, undergoes a radical re-organization. The electrons form 'Cooper pairs' and these Cooper pairs condense into a single, collective quantum state, which means they all behave as a single entity. This allows the manifestation of quantum-mechanical effects, which are normally confined to the world of sub-microscopic particles, on a scale that is visible to the naked eye.

The atomic-scale crystal structure of LaNiGa2.
Credit: Image courtesy of University of Huddersfield

Researchers at the Rutherford Appleton Laboratory and at the universities of Kent, Bristol and Huddersfield, in England, have discovered a new class of very exotic unconventional superconductors.

Superconductivity is one of the most fascinating phenomena known to humankind. When a superconductor is cooled below its 'critical temperature', the fluid of electrons, which is responsible for the conduction of electricity through the material, undergoes a radical re-organization. The electrons form 'Cooper pairs' and these Cooper pairs condense into a single, collective quantum state, which means they all behave as a single entity. This allows the manifestation of quantum-mechanical effects, which are normally confined to the world of sub-microscopic particles, on a scale that is visible to the naked eye.

Much recent research on superconductivity has focused on the internal structure of these Cooper pairs. While in conventional superconductors (and also in some high-temperature superconductors) the electrons in a Cooper pair have their intrinsic 'spins' pointing in opposite directions, so that the total spin of the Cooper pair is zero, in other, more exotic 'triplet' superconductors the electronic spins line up, so the Cooper pair has some intrinsic spin of its own. Such is the case, for example, of the strontium ruthernate Sr2RuO4, which is the paradigmatic example of a triplet superconductor. However, whereas in Strontium Ruthenate the Cooper pair spins are randomly-oriented, so that there is no net spin of the condensate of Cooper pairs in this material, in other, even more exotic 'non-unitary' triplet superconductors the spins of the Cooper pairs point in a particular direction. This comes about because the electrons whose spins point in that direction are more likely to form a pair than other electrons.

Until very recently, however, all known non-unitary triplet superconductors where so for a fairly simple reason, the materials were ferromagnetic, meaning that they were naturally magnetized and therefore even before the onset of superconductivity the spins of their electrons, which act as tiny bar magnets, were already aligned in a given direction. This changed in 2009 when three of the present authors reported measurements and theoretical analysis suggesting that the superconductor LaNiC2 was a non-unitary triplet superconductor [A. D. Hillier, J. Quintanilla and R. Cywinski, Phys. Rev. Lett. 102, 117007 (2009)]. This was surprising because LaNiC2 is not ferromagnetic, meaning that there had to be some as yet unknown mechanism whereby the electrons that paired up in Cooper pairs did so with their spins aligned in a particular direction. How did they chose this direction? Did the unusual crystal structure of this material, which unlike most crystal lattices is not symmetric under inversion, have something to do with it?

Now the present team has produced evidence of another material having this exotic property, namely LaNiGa2. Like in the previous case, the measurements were carried out using the muon spin rotation technique at the ISIS Facility, Rutherford Appleton Laboratory. In this technique, a powerful particle accelerator is used to bombard a sheet of graphite with a proton beam, producing muons, a subatomic particle that is then implanted in the material to be studied. After a few microseconds, the muon disintegrates, emitting a positron that is detected by the experimental apparatus. The direction of emission of the positron contains information about the atomic-scale distribution of magnetization inside the material.

Unlike its cousin LaNiC2, the crystal structure of the new superconductor does have symmetry under inversion, but the chemical similarity of the two compounds suggests that they are two instances of a new family of superconductors that have non-unitary triplet pairing even though they are not ferromagnetic. In this latest publication, the team puts forward a possible explanation, they show, by a very general reasoning based on the fundamental symmetries of nature, that the natural tendencies in these materials to magnetize under the influence of an externally-applied magnetic field, what is called 'paramagnetism', can lead to the development of a magnetization in response to the magnetic moments of the Cooper pairs themselves. In other words, rather than relying on some pre-existing magnetization, the magnetic moments of the Cooper pairs themselves create the magnetism that is required for their magnetization to be energetically favorable -- thus non-unitary triplet pairing can lift itself by its bootstraps. This would be a superconducting analogue of the way magnetism develops in ferromagnetic metals. A confirmation of this scenario would be quite spectacular, as it is a new form of magnetism that is generated by superconductivity.

The discovery of a new family of unconventional superconductors is a rare event. The challenge now is to reach a microscopic understanding of how this highly-exotic pairing structure comes about. There will also be a race to find more examples of this family as well as more experimental evidence, obtained with other techniques, of this unusual phenomenon.


Story Source:

The above story is based on materials provided by University of Huddersfield. Note: Materials may be edited for content and length.


Journal Reference:

  1. A. D. Hillier, J. Quintanilla, B. Mazidian, J. F. Annett, and R. Cywinski. Nonunitary triplet pairing in the centrosymmetric superconductor LaNiGa2. Physical Review Letters, 2012 [link]

Cite This Page:

University of Huddersfield. "New class of unconventional superconductors." ScienceDaily. ScienceDaily, 3 July 2012. <www.sciencedaily.com/releases/2012/07/120703161532.htm>.
University of Huddersfield. (2012, July 3). New class of unconventional superconductors. ScienceDaily. Retrieved October 23, 2014 from www.sciencedaily.com/releases/2012/07/120703161532.htm
University of Huddersfield. "New class of unconventional superconductors." ScienceDaily. www.sciencedaily.com/releases/2012/07/120703161532.htm (accessed October 23, 2014).

Share This



More Matter & Energy News

Thursday, October 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

3D Printed Instruments Make Sweet Music in Sweden

3D Printed Instruments Make Sweet Music in Sweden

Reuters - Innovations Video Online (Oct. 23, 2014) Students from Lund University's Malmo Academy of Music are believed to be the world's first band to all use 3D printed instruments. The guitar, bass guitar, keyboard and drums were built by Olaf Diegel, professor of product development, who says 3D printing allows musicians to design an instrument to their exact specifications. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Chameleon Camouflage to Give Tanks Cloaking Capabilities

Chameleon Camouflage to Give Tanks Cloaking Capabilities

Reuters - Innovations Video Online (Oct. 22, 2014) Inspired by the way a chameleon changes its colour to disguise itself; scientists in Poland want to replace traditional camouflage paint with thousands of electrochromic plates that will continuously change colour to blend with its surroundings. The first PL-01 concept tank prototype will be tested within a few years, with scientists predicting that a similar technology could even be woven into the fabric of a soldiers' clothing making them virtually invisible to the naked eye. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Jet Sales Lift Boeing Profit 18 Pct.

Jet Sales Lift Boeing Profit 18 Pct.

Reuters - Business Video Online (Oct. 22, 2014) Strong jet demand has pushed Boeing to raise its profit forecast for the third time, but analysts were disappointed by its small cash flow. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
Internet of Things Aims to Smarten Your Life

Internet of Things Aims to Smarten Your Life

AP (Oct. 22, 2014) As more and more Bluetooth-enabled devices are reaching consumers, developers are busy connecting them together as part of the Internet of Things. (Oct. 22) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins