Scientists Advance Toward ‘Spin’ Computers

Scientists at the University of California, Riverside, have made a key advance in computer technology that could combine logic with nonvolatile memory, eliminating the current bottleneck between processors and memory, and potentially paving the way for “instant-on” computers.

The team, led by associate professor of physics and astronomy Roland Kawakami, said they had achieved a technique called “tunnelling spin injection” into a material called graphene, a one-atom-thick layer of graphite that is seen by some scientists as a potential successor to silicon.

Their results were published last week in the journal Physical Review Letters.

Spin injection

The technique involves injecting a spinning electron into graphene in such a way that the electron can be used to represent one bit of data. In theory the bits injected in this way can be stored in a nonvolatile state, without the need for electricity, and could be used for both storage and computations.

Kawakami’s team used a semiconductor laser to polarise electrons and give them a directional orientation, called “spin” – either “spin up” or “spin down”. Electrons polarised in this way can be used to represent either a one or a zero. Once the electrons are in place they remain there for the life of the chip.

“Spin computers, when developed, would utilise the electron’s spin state to store and process vast amounts of information while using less energy, generating less heat and performing much faster than conventional computers in use today,” the university said in a statement.

Kawakami’s team inserted a nanometre-thick insulating layer into the graphene, called a “tunnel barrier”, which improved the efficiency of the spin injection process.

“We found a 30-fold increase in the efficiency of how spins were being injected by quantum tunneling across the insulator and into graphene,” stated Kawakami. “We now have world record values for spin injection efficiency into graphene.”

Energy usage

However, the process needs to be made to use less energy, according to Kawakami – one of the key technical hurdles to be solved before a working “spin computer” can be made possible.

The team chose graphene because it is extremely strong and flexible, is a good conductor of electricity and is capable of resisting heat. The discoverers of graphene won a Nobel prize earlier this month.

“Graphene has among the best spin transport characteristics of any material at room temperature, which makes it a promising candidate for use in spin computers,” stated Kawakami.

He said the team’s next project is to demonstrate a working spin logic device. Such devices could make their way into products in five or ten years, Kawakami said.