The Wiedemann-Franz Law and Electron's Independent Spin and Charge

In 1853, Wiedermann and Franz found that elemental metals conducted electricity and heat at roughly the same ratios at the same temperature. This is because electricity moves through electrons, and heat uses electron's charge and spin to move through a 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. [1]"

In 1996, American physicists C. L. Kane and Matthew Fisher predicted that the Wiedemann-Franz Law could be violated if electrons were confined to a single dimension. Electrons in 1D would have independent charge and spin excitation. Well, they found a metal that could prove this.

Purple bronze is a metal with a one dimension electrical property, conducting heat well, but not conducting electricity. Its 1D property may have something to do with its "3D crystal, but with a quasi 1-dimensional band structure." In my own non-complicated words, it's a bunch of extremely thin wires that lie right next to each other but do not touch. This unique structure allows it to have 1D atomic chains, which is possible on 2D structure like graphene, but very unusual for complex 3D strctures. 3D structures tend to electron coupling within the complex. However, in PB, 1D atomic chains confine electrons so they can't move around very much. Because electricity depends on electron movement, PB does not transmit electricity very well. Professor Hussey of the Correlated Electron Systems Group at the University of Bristol said, "the electrons are effectively confined to individual chains and thus creating a one-dimensional world inside the three-dimensional complex." 

You might be thinking that this isn't so impressive because other compounds have one-dimensional electrical properties, as well, e.g. diamonds. Diamonds conduct heat, but not electricity. However, diamond is pure carbon, an organic element, while PB is metallic. The fact that PB breaks the rules and shares properties similar to non-metals is an interesting challenge to the Wiedemann-Franz Law, and the fact that something 1D can exist in a 3D structure will let scientists see the effects of dimension on electron charge and spin.

PB?

What is bronze? It's basically any alloy of copper and another metal. For example, tungsten oxide bronzes (copper with tungsten and oxygen) and molybdenum bronzes (copper and molybdenum) have been proposed for use as ion-selective electrodes. Purple bronze (Li0.9Mo6O17) is lithium, molybdenum, and oxygen. It's not actually a "purple bronze". The alloy named so because of its unique color, either purple or bronze, depending on the optical orientation.

Original article found here.

An article from Nature on the violation of the WF Law, but this time more on 1D nature of electron spin.
Some of this is confusing for me. By the way, the spinon and the holon mentioned are just statistical representations of group properties and not actual particles.


Purple bronze research at MSU

Posted in: physics