A Brand-new Way to Produce Electron Spin Currents

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With apologies to Isaac Asimov, the most exciting phase to hear in science isn’t “Eureka,” but “That’s funny…”

A “that’s funny” moment in a Colorado State University physics lab has led to a fundamental discovery that could play a key role in next-generation microelectronics.

Nature Physics

Publishing in Nature Physics April 25, the scientists led by Mingzhong Wu, professor of physics in CSU’s College of Natural Sciences, are the first to demonstrate using non-polarized light to produce what’s called a spin voltage – a unit of power produced from the quantum spinning of an individual electron. Controlling electron spins for use in memory and logic applications is a relatively new field called spin electronics, or spintronics, and the subject of the 2007 Nobel Prize in Physics.

Spintronics exploits the notion that electron spins can be manipulated and used to process and store information, with a fraction of the power needed in conventional electronics. Wu and his group’s passion is to find new, better ways to control electron spins, the physics of which isn’t yet completely understood.

Next-gen Electronics

Consider that the iPhone and every electronic device out there is built upon centuries of science around charge current – positive or negative charges flowing through a device. The perennial problem is the enormous power consumption of charge-current devices, and the electrical resistance that causes power loss in the form of heat – which is why your laptop keeps overheating.

These power and heat barriers limit smaller, more powerful electronics. And that’s why science is turning to spintronics, because it offers a completely new way of making a device work. No charge current is necessary to utilize power from an electron spin. All that’s needed is a magnetic field or a magnetic material, which can orient the spins “up” or “down.” The up and down spins are the analog to positive and negative charges.

Existing methods for creating spin currents include using a charge current (which kind of defeats the purpose), microwaves, or a heat source. But for the first time, the CSU team has used light – or in the quantum world, photons – to generate their spin currents.

Other scientists have done similar things, but with a special kind of polarized light. Here, the CSU scientists used plain unpolarized light – “a halogen bulb purchased at Ace Hardware,” said graduate student David Ellsworth, who is the first author on the paper. They demonstrated a “pure” spin current – involving no charge movement. It was an unprecedented feat.

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