The Wiedemann-Franz Law, named after German physicists Gustav Wiedemann and Rudolf Franz, is a ratio of the thermal to electrical conductivities of metals. In 1853, the two studied the thermal conductivity, 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. 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, two American physicists Charles 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."
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- The 10 catastrophic mistakes virtual reality firms are making
- My Thoughts On The LIGO-VIRGO Result
- Henri Poincaré Predicted The Existence Of Gravitational Waves As Early As June 5, 1905
- Gravitational Waves? Watch the LIGO press conference at 10:30 Eastern.
- Using Stories To Teach Human Values To Robots
- Four Different Ways Couples Show They Care
- How Gut Inflammation Sparks Colon Cancer
- "I am somewhat confused. Where did the three solar masses that were converted to gravity waves come..."
- "Veronique,You are right to suspect that the organic industry has been more than happy to go along..."
- "I'm not understanding yet, but this is like unravelling a fun physics puzzle. I'd thank you for..."
- "I would just like to thank the author of this article for having the balls to take a stand against..."
- "I believe the point to take away from that graph is that for much of our Earth's history the CO2..."
- Natural Flavors Are More Radioactive Than Artificial Ones.
- Bariatric Surgery Beneficial Even for Older People
- Opiates No Better at Easing Knee Osteoarthritis Pain
- BRCA Tests Increasing for Younger Breast Cancer Patients
- EWG Verified: A New Way To Greenmail Food Companies
- A Cluttered Kitchen May Undo Your Diet
- Eating breakfast could help obese people get more active
- 'Jaws' may help humans grow new teeth, shark study suggests
- For a special Valentine? Beyond diamonds and gems: The world's rarest minerals
- Most precise measurement of reactor Antineutrino spectrum reveals intriguing surprise
- Using stories to teach human values to artificial agents