Skip to comments.Bristol physicists break 150-year-old law
Posted on 07/21/2011 6:46:44 AM PDT by Red Badger
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 thermal conductivity (a measure of a systems 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. Electrons 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.
More information: Gross violation of the Wiedemann-Franz law in a quasi-one-dimensional conductor by Nicholas Wakeham, et al. in Nature Communications
Provided by University of Bristol
Damn, I just ordered an upgraded radiator for my PC cooling system. I wonder when this new metal will be in our cars and our PCs for cooling?
does this mean it conducts heat one direction and charge another direction?
The limitation of the heat exchanger is defined by the diffusivity of the fluids, not the barrier.
Why would electrical conductivity get in the way of heat exchangers? Copper works pretty well, even though it does conduct electricity.
The bronze merely has high ratio of thermal to electrical conductivity. It doesn’t necessarily have a very high thermal conductivity.
It would have to be something other than bronze to be used in nuclear power plants. Copper alloys are verboten now, and even a lot of fossil plants are getting rid of copper alloys as the copper tends to leach out and foul steam generators and boiler tubes.
Ping for later. This looks good.
Nope. It means it conducts heat in one direction and doesn’t conduct charge hardly at all...
Gravity: It’s Not Just a Good Idea It’s the Law
This needs to be outlawed immediately because it might be worse than cow farts in contributing somehow to global warming
By the time your car is ready for the junk heap and your computer makes a nice conversation piece in your curio cabinet...............
I see an immediate market for purple bronze cannons.
Or purple bronze rifle barrels.................
So... is that just a misdemeanor, or are they going to have to do jail time?
This research merely proves that they can break this ‘law’ under certain conditions. The metal used was just the beginning. If it can be done with this metal combo, then it most likely can be done with other metal combos as well...................
I think metal combos would not taste very good.
I always give a shudder over the abuse of the terms ‘law’ ‘theory’ ‘hypothesis’ etc
How dare anyone challenge scientific consensus!
I guess the cupronickel tubes and tubesheets in heat exchangers would be out of the question then. Unfortunately most nuclear plants have dozens of these style of shell and tube heat exchangers in operation. Stainless steel doesn’t conduct heat nearly as well as most copper alloys.
Not to step on your toes or anything, but I built a lot of replacement parts for those heat exchangers.
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