WIRE PRODUCTION

The tiny wires are created at the Chair held by Ralph Claessen. “We steam gold atoms onto little plates made of germanium, which are one centimetre in length and three millimetres wide. This is done in ultra-high vacuum equipment at a temperature of 500 degrees celsius,” states associate professor Jörg Schäfer, whilst at work in the laboratory.
Thanks to a sophisticated process the physicists in Würzburg can load the blanks in such a way that the gold atoms arrange themselves into straight, parallel chains, thus creating the nano wires. The wires are far enough apart not to influence one another – which is vital for conducting further research into them.

Nano wires: Possible applications

But what can these wires potentially be used for? “They consist of individual atoms which means it is practically impossible to make electrical conduits that are any smaller,” says Jörg Schäfer. As a result, the nano wires could possibly be used to make components that push the miniaturisation of computers to its limits. The vision of one day demonstrating the world’s smallest quantum computer is one that has great appeal to the Würzburg physicists.
At present, they are mainly using the nano wires as an atomic playground. “We can expand the wires on their sides by adding individual gold atoms. Or else, we can create cross bridges between them. And then we can analyse how this changes their electronic attributes,” explains Professor Claessen.
And their next aim? The team in Würzburg hopes to succeed in influencing the nano wire’s electrical conductivity. “This can be done with the help of additional atoms. Using the tip of a scanning tunneling mircroscope, we can also fill a wire with an electrical charge, making it possible to switch it on and off in a controlled manner. By removing the additional atom or allowing the charge to flow away, the wire would be switched on again,“ says Schäfer. And if this works, would implications would it have? Basically, it would create a fundamental prerequisite for using nano wires as components in quantum computers.

Amazing phenomena in nano structures

The electrical circuit of a nano wire can also lead to new findings of a more fundamental nature. The smaller a solid body is, the greater the surprises concealed within it. “Many astounding phenomena occur in nano-structures that contradict our intuition as physicists,” states Schäfer.
Why is this so? These structures are so tiny that the electrons, the carriers of the electrical charge, can only move along a tightly enclosed path – that is, along the wires. In a conventional piece of metal the electrons can move in many different directions. However, when the electrons are enclosed in a tiny space so that they cannot avoid one another, unusual quantum effects occur. This can, above all, affect electrical conductivity.

A model for Luttinger liquids?

The physicists in Würzburg believe that their nano wires represent an innovative model system for one-dimensional electron liquids. In concrete terms, they are hoping to observe a so-called Luttinger liquid. This is the term physicists give to electrons that can only move in one dimension – in this particular case, along the length of the nano wires.
“However, it is really difficult to prove in the lab the properties of a Luttinger liquid as predicted in theory,” states Schäfer. “However, we have come across first indications. Luckily, the innovative nano wires remain conductive even at the low temperatures required to make the necessary tunnel spectroscopy measurements.”
The team in Würzburg details its arguments in an article for the Physical Review Letters. The editors believe the article to be of significant importance and have, therefore, highlighted it as the Editors' Suggestion: This title indicates to readers that the report is of interest to physicists from all fields.
“New Model System for a One-Dimensional Electron Liquid: Self-Organized Atomic Gold Chains on Ge(001)”, J. Schäfer, C. Blumenstein, S. Meyer, M. Wisniewski and R. Claessen, Phys. Rev. Lett. 101, 236802 (2008), doi 10.1103/PhysRevLett.101.236802

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