Researchers Induce Superconductivity in an Insulator

Nov 24, 2008 By Laura Mgrdichian feature

( -- To continue to improve semiconductor devices, such as transistors, which form the backbone of the consumer electronics industry, researchers need to be able to control the movement and density of the electric charge within them.

Many scientists are particularly interested in finding ways to increase the maximum density of charge in semiconductor devices. Doing so could lead to a major achievement in semiconductor research: inducing superconductivity in field-effect transistors (FETs) -- tiny semiconductor-based devices essential to integrated circuits (a single computer chip can contain millions). FETs could be vastly improved, eventually leading to better products for consumers.

One key way to control charge density is by mixing in impurity atoms, a process called doping. Another way is using external electric fields. But in the latter method, problems arise with FET types that have insulating layers, such as the metal-oxide-semiconductor FET, or MOSFET (where the oxide layer is an insulator).

Recently, researchers from Tohoku University in Sendai, Japan, and the Japan Science and Technology Agency demonstrated that it is possible to make an insulator superconduct within an FET structure. In the October 12 online edition of Nature Materials, the scientists describe their unusual FET structure, which incorporates an organic current-carrying material (an electrolyte) consisting of a polymer mixed with a salt.

The basic structure is layered: a top platinum electrode, the electrolyte, and strontium titanate (SrTiO3), a mineral and strong insulator. Attached to the SrTiO3 surface are two gold islands that serve as electric leads and contacts. The total structure has a thickness of only a few hundred nanometers (billionths of a meter).

When a voltage is applied across the platinum layer and gold contacts using a battery, turning the structure "on," the effect is of a double-layer capacitor. The voltage splits the positive and negative ions in the electrolyte, sending negative charge to upward to the platinum surface and positive charge downward. This induces a very large negative "image" charge on the SrTiO3 surface, forming a conduction path between the two gold contacts. The electrolyte acts as a dielectric, an insulating material used between two capacitor plates to allow more charge to be stored before the capacitor breaks down.

Corresponding author Masashi Kawasaki, who is affiliated with both Tohoku University and the Japanese Science and Technology Agency, told, "The problem with past attempts to use electric fields to induce superconductivity in an insulator is there were no dielectric materials that could sustain a high enough field to build up the necessary charge in the insulator. So instead of the standard dielectric oxide, we've used a conducting polymer."

Using this method the researchers increased the SrTiO3 charge-carrier density from zero to approximately 10 trillion carriers per square centimeter. When cooled down to 0.4 K (about -460 degrees Fahrenheit), it becomes superconducting.

Kawasaki and his colleagues think their approach is a promising way to discover superconducting behavior in other unlikely materials.

"We do not need to worry about the complicated chemistry involved in mixing materials. All we need is a polymer and a battery. This way of making a superconductor may open a door to unexplored superconducting materials," said Kawasaki.

Citation: K. Ueno, S. Nakamura, H. Shimotani, A. Ohtomo, N. Kimura, T. Nojima, H. Aoki, Y. Iwasa and M. Kawasaki, Nature advance online publication 12 October 2008; doi:10.1038/nmat2298

Copyright 2007
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of

Explore further: Physical constant is constant even in strong gravitational fields

add to favorites email to friend print save as pdf

Related Stories

Mass spectrometry in your hand

Sep 09, 2014

If you're out in the field doing environmental testing, food checks, forensic work, or other chemical analysis, mass spectrometry is an extremely accurate detection tool with one huge drawback: You can lose ...

Omni3D's big idea: Wind turbines in backpacks

Aug 18, 2014

Mention wind energy and one thinks on a large-scale, a farm of structures, tracts of land, multi-year roadmaps, and a web of public and private agencies signing off on agreements and contracts over months ...

Doped graphene nanoribbons with potential

Sep 08, 2014

Graphene is a semiconductor when prepared as an ultra-narrow ribbon – although the material is actually a conductive material. Researchers from Empa and the Max Planck Institute for Polymer Research have ...

Recommended for you

How Paramecium protozoa claw their way to the top

12 hours ago

The ability to swim upwards – towards the sun and food supplies – is vital for many aquatic microorganisms. Exactly how they are able to differentiate between above and below in often murky waters is ...

User comments : 5

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Nov 24, 2008
cool.and cold.

1 / 5 (1) Nov 24, 2008
a polymer and a battery... hey you never know!!!!!
1 / 5 (2) Nov 25, 2008
This results corresponds the AWT mechanism of superconductivity - a highly compressed electrons are moving without friction through material, because their repulsive forces are stronger, then those between electrons and other atoms.

The problem in using of this mechanism for energy transmission is, how to compress electrons at larger scales - but this system can result into new kind of superconductive FET switches with zero resistance in connected state.
not rated yet Nov 28, 2008
I wonder if this could be used on a large scale in hybrid cars and solar panals to make them more efficient. It seems like this would be relatively cheap to manufacture.
not rated yet Feb 04, 2009
The only problem is, we're required to use very stiff and inert material at the same moment, capable to keep holes in it even under strong electrostatical field intensity. Currently only diamond was proven to be able to keep holes in the form of oxide atoms and able to form a superconductive layer at the surface.