'Impossible' conductivity explained

May 19, 2010
'Impossibleconductivity explained
In a stacked atomic structure of lanthanum oxide with a strontium titanate capping layer on a substrate of strontium titanate (crystal structure from left to right, top of illustration), the internal potential in the LAO layer brings about a redivision of charge. The resulting electrons on the interface leave behind holes that are just one nanometre apart. The electrons (left) and gaps (right) in parallel produce a contribution to the electrical conductivity.

(PhysOrg.com) -- Bring two materials that are not themselves conductive into contact and, exactly at their interface, something remarkable happens: at that precise point, conduction is possible.

Researchers from the MESA+ Institute for of the University of Twente, The Netherlands, together with colleagues from Munich, Berkeley and Davis, have now also demonstrated that at this interface two parallel conductive ‘paths’ are created, just one nanometre apart. That is not only a breakthrough in our understanding of the phenomenon, it also opens up possibilities for new forms of nanoelectronics. The researchers have published their findings in .

The researchers from the University of Twente had earlier demonstrated that two non-conductive metal oxides could become conductive at the exact point where they come into contact, and that non-magnetic metal oxides 'suddenly' become magnetic at their interface, for example in the combination of strontium and aluminate. When these two complex oxides come into contact, various are present on both crystal interfaces, all with their own charges. When the two oxides come into contact, a rearrangement of the charge, known as electronic reconstruction, takes place.

At the point where the are more numerous, these electrons can now conduct electricity. At the same time, it would be expected that holes - positive charge carriers - would be created elsewhere in the structure, where the original electrons were located. The new calculations and experiments have now shown that these holes do indeed exist, and that the holes and the electrons move in parallel to each other, with a space of just one nanometre between them. This is not only a breakthrough in the understanding of conduction at the interface, it also opens up the way for new applications that are not yet possible in current semi-conductor electronics. One exciting possibility, for example, is that interaction might also occur in these conductive layers, which are so close together, with new particles and quantum states as a result.

What is more, until now it was assumed that oxides with a specific thickness were needed to achieve this effect. However, the newly published research shows that the mechanism occurs even with a thickness of a single unit cell: just one layer in the crystal. The MESA+ Institute for Nanotechnology has unique facilities for building up these types of oxides atomic layer by atomic layer, and in this way creating materials with an astonishingly wide range of properties.

Explore further: Controlling defects in engineered liquid crystals

More information: The article 'Parallel Electron-Hole Bilayer Conductivity from Electronic Interface Reconstruction', by R. Pentcheva et al. has already been published online on the website of Physical Review Letters and will soon appear in print. (prl.aps.org/)

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May 19, 2010
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not rated yet May 19, 2010
I'm going to say something that I never imagined I would have to say: Hubbard was right.

Before he started his religi-con he was a SciFi writer and wrote a (very bad) novel called Battlefield Earth. In this novel the aliens carve paths into isolator material and that path conducts electricity.

Who woulda thought that he was right on the money with that one o_O ?
5 / 5 (2) May 20, 2010
antialias: isn't this more a case of a million monkeys typing the works of Shakespeare rather than of being correct about a natural phenomenon?
not rated yet May 20, 2010
Maybe because there are more things possible that we could ever imagine. Im really glad im living in this period of time when we realize that.
not rated yet May 20, 2010
Can't wait until johanfprins sees this article. He'll be jumping for joy at validation of some of his hypotheses but he'll be furious that the charge carrier statements are still contrary to his core statements.
not rated yet May 21, 2010
Maybe because there are more things possible that we could ever imagine. Im really glad im living in this period of time when we realize that.
Well, in former times people used to know about that. And were frightened.
not rated yet May 21, 2010
..he'll be jumping for joy at validation of some of his hypotheses..
I presume not - this is rather classical phenomena, which has nothing to do with superconductivity and charge waves in addition. You're just confused by many concepts presented here.

We can prepare semiconductor, the conductivity of which will be increased by some strong donors. If you add many weak acceptors to it, then the conductivity will be decreased again. Now we can prepare another piece of insulating superconductor in the opposite way: with a few strong donor dopants and many weak acceptor ones.

What will happen in mutual contact of both these semiconductor materials? The concentration of both types of charge carriers would compensate at different distance from contact - and as the result, the pair of conductive diodes will be formed there.

After all, this principle doesn't differ very much from production of FET transistors, which are using the resulting conductive channel for switching purposes
3.7 / 5 (3) May 21, 2010
You can find a MOSFET animation there - so you can see, it basically works in the same way, like the "impossibly conductive" system presented above:


The fast increasing volume of human knowledge makes often difficult to recognize well known and used concepts from these very new ones. This is an undeniable consequence of informational explosions.

As the result, many half-educated skeptics here are fighting against quite trivial conclusions, just because they don't know/understand all their connections of background. Or vice-versa: they're accepting many ideas in noncritical way as a very new impressive findings.
May 23, 2010
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