Neutrons cast serious doubt on major 'suspect' in search for origin of high-temperature superconductivity

Nov 20, 2013 by Andrea Piovano

Superconductivity, the property of certain metals of opposing zero resistance to the passage of an electric current when cooled down below a critical temperature Tc is a highly prized property in both scientific research and industry. Able to form powerful low-consumption electromagnets, they are already used in MRI and NMR machines, mass spectrometers, and particle accelerators. The still relatively low temperatures required to induce this valuable property however, currently restrict wider commercial exploitation.

Progress in attaining superconductivity at higher temperatures was in the past mainly driven by fortuitous discovery. This is a rather unsatisfying situation. For researchers to optimise and finally engineer the properties of a thorough understanding of the superconducting mechanism would be desirable. This understanding is still lacking for the superconductors operating at elevated temperatures.

A popular suspect for causing superconductivity in high Tc materials is charge stripes. The stripes are created by a process known as 'doping' where an element with a different number of electrons (usually less electrons) is introduced into the buffers between the superconducting layers thus creating a charge reservoir that either may pump electrons into the layer or may extract electrons from the layers thus creating holes. These extra electrons or holes have a propensity to organize themselves into stripes. While these stripes can be observed directly when static they become difficult to observe when fluctuating. As it is the fluctuations that are supposed to play an important role in high-Tc superconductivity – no static charge stripes are observed- we have to look for indirect evidence. So far charge stripes were always accompanied by a very specific magnetic excitation spectrum given the name of 'hourglass' spectrum. Hourglass spectra are equally a hallmark of high-Tc superconductors. It was, therefore only logical to conjecture that hourglass spectra are conditioned by charge stripes and that fluctuating charge stripes should be present in the high Tc materials.

To investigate this relationship further a team or researchers from the Max-Planck-Institute in Dresden, Germany working at the ILL in Grenoble and LLB in Saclay studied the magnetism, magnetic excitations, charge ordering and electron–phonon coupling in a stripeless single-layer perovskite cobaltate compound. Whilst the compound was similar in structure and make-up to the compounds studied previously that produced the hourglass dispersion patterns, the lack of stripes should, according to the popular belief, produce no such excitation patterns.

And yet, in a new paper published in Nature Communications the team did indeed observe a familiar magnetic excitation spectrum with all the basic features of an hourglass spectrum. Their findings dismiss the link between the stripes and the hourglass dispersion in this cobaltate material.

As well as cautioning researchers when it comes to the stripe theory of superconductivity, the team also provided some evidence to support alternative causes of the hourglass excitations. In their paper they suggest that a magnetic effect known as frustration, where atoms within the crystal lattice are prevented from aligning with respect to each other due to the conflicting demands they receive from all the neighbouring atoms, creates a perfect balance of interaction that could account for the hourglass spectrum. This is particularly interesting as it links two highly active research fields that of and that of frustrated magnetism.

Explore further: Electron spin could be the key to high-temperature superconductivity

More information: "Hour-glass magnetic spectrum in a stripeless insulating transition metal oxide" Y. Drees, D. Lamago, A. Piovano, A. C. Komarek, Nature Communications 4, Article number: 2449. DOI: 10.1038/ncomms3449 Published 19 September 2013

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User comments : 5

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RealScience
2.3 / 5 (3) Nov 20, 2013
The progress in superconductor research is slowed down with the fact, the physicists are using it as a salary and job generator too - and when this research will finish, their jobs will end as well.


Bull.
In addition to typically being driven by curiosity, each individual scientist has an incentive to speed up his or her research to publish first (and this, rather than being slow, helps them keep a job or even get promoted).
Also, if anyone produces a practical room-temperature superconductor, there will be so many jobs in the resulting industry that essentially all good superconductor scientists will have high-paying private-sector job offers.

The work goes slowly because it is a hard problem.
Simca
Nov 25, 2013
This comment has been removed by a moderator.
Zephir_fan
Nov 25, 2013
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Simca
Nov 25, 2013
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Zephir_fan
Nov 25, 2013
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NOM
not rated yet Nov 25, 2013
A disguise? Do you mean underwear?
If you're wearing it on your head, then we'll know it's zephyr
Teemu
5 / 5 (1) Nov 25, 2013
Simca,

Why does Joe Eck only manage to increase the critical temperature but not the volume fraction, the proportion of the sample that is superconductive?

The critical temperature keeps on rising and rising, now supposedly well beyond room temperature, but the fraction of supposedly superconductive material stays small. If he is developing his materials systematically based on somekind of insight, the volume fraction should also go up.

If the activity on the MT curve is measurement error, or one of the other possible phenomena than superconducting transition, "increasing the critical temperature" obviously is considerably easier than increasing the yield, because you can keep trying to find this non-sc phenomena or error on the data from the higher temperatures, but obviously you can't you can't increase the volume fraction...

There is plenty of articles, discussion in the internet, about what other stuff than superconductivity can cause interesting looking stuff on the M-T curve.
Teemu
5 / 5 (1) Nov 25, 2013
But because the physicists are jealous and selfish, they don't like to participate on research, which someone else already proved sucessfull. After all, they have nowhere to hurry until their money are going.


Yeah, just like in1986 and 1987 nobody was willing to repeat and improve upon the experiments of Bednorz and Mueller, who had already succesfully proved that cuprates can be superconducting at relatively high temperature compared to previously know superconductors.

Even today really few people believe that cuprates can be superconducting at relatively high temperatures, because nobody was willing to repeat and improve upon the experiments of Bednorz and Mueller.

Seriously, the history of cuprates prooves how crap that "conspiracy theory" is. The discovery of cuprates as HTSC was a huge funding boon to everybody working in the SC field, just like the next SC breakthrough, no matter where it comes from, will be a boon for pretty musch all SC scientists.
Simca
Nov 25, 2013
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Simca
Nov 25, 2013
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Simca
Nov 25, 2013
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Minich
not rated yet Dec 18, 2013
The 1st mistake was done by the nobel cometee was in 1969 in awarding Lev Landau the NOBel Prize for the theory of superfluidity in HeII.

1. The first mistake was done by awarding by the experimenter Piotr Kapitsa the SECOND in turn.
2. The second mistake was done by preventing NN Bogoliubov from before Lev Landau. Landau had stolen an idea of rotons from NN Bogolubov. An idea of rotons was not done by Bogoljubov to an end.

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