Bristol physicists break 150-year-old law

Jul 20, 2011
Bristol physicists break 150-year-old law
Apparatus from the original 1853 paper in which the Wiedemann-Franz Law was first established

(PhysOrg.com) -- A violation of one of the oldest empirical laws of physics has been observed by scientists at the University of Bristol. Their experiments on purple bronze, a metal with unique one-dimensional electronic properties, indicate that it breaks the Wiedemann-Franz Law. This historic discovery is described in a paper published today in Nature Communications.

In 1853, two German physicists, Gustav Wiedemann and Rudolf Franz, studied the (a measure of a system’s ability to transfer heat) of a number of elemental metals and found that the ratio of the thermal to electrical conductivities was approximately the same for different metals at the same temperature.

The origin of this empirical observation did not become clear however until the discovery of the electron and the advent of quantum physics in the early twentieth century.  have a spin and a charge.  When they move through a metal they cause an electrical current because of the moving charge.  In addition, the moving electrons also carry heat through the metal but now it is via both the charge and the spin.  So a moving electron must carry both heat and charge: that is why the ratio does not vary from metal to metal.

For the past 150-plus years, the Wiedemann-Franz law has proved to be remarkably robust, the ratio varying at most by around 50 per cent amongst the thousands of metallic systems studied.

In 1996, American physicists C. L. Kane and Matthew Fisher made a theoretical prediction that if you confine electrons to individual atomic chains, the Wiedemann-Franz law could be strongly violated.  In this one-dimensional world, the electrons split into two distinct components or excitations, one carrying spin but not charge (the spinon), the other carrying charge but not spin (the holon).  When the holon encounters an impurity in the chain of atoms it has no choice but for its motion to be reflected.  The spinon, on the other hand, has the ability to tunnel through the impurity and then continue along the chain.  This means that heat is conducted easily along the chain but charge is not.  This gives rise to a violation of the Wiedemann-Franz law that grows with decreasing temperature.

The experimental group, led by Professor Nigel Hussey of the Correlated Electron Systems Group at the University of Bristol, tested this prediction on a purple bronze material comprising atomic chains along which the electrons prefer to travel.

Remarkably, the researchers found that the material conducted heat 100,000 times better than would have been expected if it had obeyed the Wiedemann-Franz law like other metals.  Not only does this remarkable capability of this compound to conduct heat have potential from a technological perspective, such unprecedented violation of the Wiedemann-Franz law provides striking evidence for this unusual separation of the spin and charge of an electron in the one-dimensional world.

Professor Hussey said: “One can create purely one-dimensional atomic chains on substrates, or free-standing two-dimensional sheets, like graphene, but in a three-dimensional complex solid, there will always be some residual coupling between individual chains of atoms within the complex that allow the electrons to move in three-dimensional space.

“In this purple bronze, however, nature has conspired to limit this coupling to such an extent that the electrons are effectively confined to individual chains and thus creating a one-dimensional world inside the three-dimensional complex.  The goal now is to find a way, for example, using pressure or chemical substitution, to increase the ability of the electrons to hop between adjacent chains and to study the evolution of the spin and charge states as the three-dimensional world is restored within the material.”

Explore further: Serial time-encoded amplified microscopy for ultrafast imaging based on multi-wavelength laser

More information: ‘Gross violation of the Wiedemann-Franz law in a quasi-one-dimensional conductor’ by Nicholas Wakeham, et al. in Nature Communications

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User comments : 21

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jimbo92107
5 / 5 (2) Jul 20, 2011
Sounds like a thin sheet of purple bronze would make a very good insulator. Also sounds like the chains in the material conduct heat almost like photons are conducted in fiber optic cable.
SteveL
5 / 5 (5) Jul 20, 2011
An electrically insulative thermal conductor would work wonders in electronic cooling.
gwrede
5 / 5 (1) Jul 20, 2011
Cool. My first thought is, doesn't this mean that while an electric current goes through a metal, there should be a difference in how well the metal conducts heat in different directions? Heat would flow "with the electrons" better than in the opposite direction.
LKD
not rated yet Jul 20, 2011
I was thinking quite the opposite, that this technology could help dissipate heat from computers more efficiently and with less intrusion. Or possibly and more importantly, in space based equipment.
Isaacsname
3 / 5 (1) Jul 20, 2011
This has potential for thermoelectrics ?
hush1
1.7 / 5 (6) Jul 20, 2011
Well, I am living in the past (730 days). I wasn't aware of spinons and holons. I considered myself well-informed scientifically until now.

http://io9.com/53...d-holons

I have no excuse for this ignorance or oversight. I guess I will be asked to leave Physorg. now.
lol
Before I am asked to leave - to my defense. I was me who discovered the origins of all human language. It is not as if I did not contribute anything to science.
:)
hush1
2 / 5 (8) Jul 20, 2011
Banish me now. Force me to rest on my laurels.
I will tell you how that is later on.
lol
LuckyBrandon
not rated yet Jul 20, 2011
sooo...electrical conduit on a metal that consists of primarily copper huh....I would be looking at how the copper melted in and see if the alignment follows that (maybe higher concertrations of copper in those specific places)....

im tired, so maybe i misunderstood...enlighten me...
Shelgeyr
4.3 / 5 (6) Jul 20, 2011
Bristol physicists break 150-year-old law


Universe sues, demands compensation if not compliance (it's a civil matter).
typicalguy
5 / 5 (3) Jul 20, 2011
Shelgeyr, will they ever learn that these prohibition laws never work? The electrons find ways to
Shelgeyr
4 / 5 (4) Jul 20, 2011
Yeah, you may call yourself "typicalguy"... Right! You're an ELECTRON, aren't you??? I've got you dead to rights! I've got my voltmeter, and my oscilloscope ready to rock, and (here's my Scientific! proof!!!1!!eleventy!!!)... You wouldn't even show up on my MONITOR if you weren't in league with the electrons!!!

"Typicalguy" my positron!

[ooops, gotta run, sounds like Shelgeyr is coming back into the room...]

Whatthe?
mattytheory
5 / 5 (2) Jul 20, 2011
And that isn't a joke either. It won't matter if they hire Johnnie Cochran for their defense. When the Universe sues, it wins. Period.

Anyhow, interesting article. Now, if they could only find a way to somehow integrate this into my CPU...
hush1
5 / 5 (1) Jul 21, 2011
lol
Creative humorous associations.
Vocabulary. Can be strange in any language.
lqtoai
5 / 5 (1) Jul 21, 2011
it is a nice paper about holon and spinon. while holon is reflected by impurities, spinon is not. It means that holon can be confined by impurities, or charge is confined by impurities. I wonder whether there is something similar to electron in quantum well with seperated energy levels.
Shelgeyr
3.7 / 5 (3) Jul 21, 2011
@lqtoai, I take great effort to derail this thread with (obviously amateur-level) humor, and there you go - dragging Science back into it!

Good going! 5 stars! (really)

But seriously, I was doing some light reading recently on the principles of charged particle acceleration (http://www.fieldp.com/cpa.html , scroll down to the pdf link, but be warned it is an 11.3 MB, 593 page textbook) and I am still unclear about how this happens. I'll admit that I have no clue about the precise meaning (much less the mechanics behind) this phrase:
The spinon, on the other hand, has the ability to tunnel through the impurity and then continue along the chain.


What's going on when the spinon "tunnels through the impurity"? Why is the holon reflected by impurities? Does its charge partially discharge? (Or, what causes the change in vector?)

Makes my head spin. I wonder if "charge posturing" amongst the quarks fits into this somewhere, and if so... how?
Ricochet
5 / 5 (2) Jul 21, 2011
I recently received a transmission from my future self on the Feynman radio concerning this article...

I said, "as soon as we discover the 3rd family of hadrons, which will be known as morons, we'll truly understand the nature of the universe."
Shelgeyr
1 / 5 (1) Jul 21, 2011
Ricochet, Thank you!

The force of the morons should be measured in oblivions.
mattytheory
5 / 5 (1) Jul 21, 2011
I don't know if this guy is correct but he made sense of this for me. Check the comments section for an explanation by Cloudypants:

http://io9.com/53...s-spinon
s-and-holons
JadedIdealist
not rated yet Jul 22, 2011
Diamond (sometimes known as ice) is an excellent thermal conductor and very poor electrical one.
The law was always limited to metals.
Now it's limited to a subclass of metals.
stealthc
not rated yet Jul 23, 2011
when can I get one for the heatsink in my laptop?
lqtoai
not rated yet Jul 23, 2011
It sounds interesting. Electrons possess holons with charge and spinons with spins. When holons are close together, they will repel each other with Coulomb force, and spinons do not suffer this strong force. However, like magnets, spin has magnetic interaction between each other, I guess if two spins are antiparallell, their interaction differs from one of parallell spins.
in the other word, I wonder if I have a spin polarized current with one spin (let's suppose spin up current), and this current is blocked by magnetic impurities. Then the tunelling behavior of the spinon of the current will depend on spin of impurities, while holon is reflected. Does it make sense?