Graphene insulators pave way for quantum computing

23 December 2013
By Tereza Pultarova
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Researchers have changed properties of graphene making it act as a topological insulator

Researchers have changed properties of graphene making it act as a topological insulator [Credit:MIT]

American researchers have discovered how to make graphene capable of filtering electrons according to their ‘spins’, opening new possibilities for future quantum computing.

Taking advantage of the so-called Hall Effect, the team from the Massachusetts Institute of Technology (MIT), led by professors Pablo Jarillo-Herrero and Ray Ashoori managed to alter the behaviour of the wonder material making electrons with positive spins to move clockwise around the conductive edge of a graphene sheet and those with negative spins to circle anti-clockwise. The study has been published in the latest issue of the journal Nature.

“We created an unusual kind of conductor along the edge, virtually a one-dimensional wire,” said Andrea Young, a Pappalardo Postdoctoral Fellow in MIT’s physics department, explaining that segregation of electrons according to their spins is a normal feature of topological insulators. However, graphene is not normally a topological insulator.

“We’re getting the same effect in a very different material system,” Young said.

Under normal circumstanced sheets of graphene behave as normal conductors. When voltage is applied, the electric current flows throughout the two-dimensional flake. If a graphene flake is, in addition, subject to a magnetic field perpendicular to the flake itself, its behaviour changes with current flowing only along the edge and the bulk becoming an insulator. In such a situation, electric current flows only in one direction, either clockwise or anti-clockwise, depending on the orientation of the magnetic field. This phenomenon is known as the quantum Hall effect.

In the newest experiment, the MIT researchers discovered that if a second powerful magnetic field is applied, this time in the same plane as the graphene flake, electrons with different spins start moving in different directions.

“We can turn these edge states on and off,” Young said, explaining that such capability would allow creating graphene circuits and transistors, possibly paving the way for future quantum computers.

The experiment was conducted using a magnetic field of about 35 Tesla - ten times stronger than an MRI scanner - at temperatures about 0.3 degrees Celsius above absolute zero.

According to Jarillo-Herrero, the Mitsui Career Development Associate Professor of Physics at MIT, such behaviour in graphene has previously been predicted but never actually observed.

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