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Breakthrough controls the spin of electrons via all electric means

Many of the electronic devices in your home transmit data by controlling the movement of the charge in an electron. Researchers and scientists have found that by using a different means that controls the spin of an electron rather than its charge, transistors would require less energy and create less heat while being able to operate at faster speeds.

The field of research into controlling the spin of an electron is called spin electronics or spintronics for short. A group of researchers at the University of Cincinnati has developed a novel way to control the spin of electrons using pure electric means. The researchers have published their findings in Nature Nanotechnology.

Before the researchers made their breakthrough, the only way to control the spin of electrons was by using local ferromagnets in device architectures. The scientists say that this technique results in design complexities when the demands for electronics require smaller and smaller transistors.

Philippe Debray, research professor in the Department of Physics in the McMicken College of Arts & Sciences said, "Until now, scientists have attempted to develop spin transistors by incorporating local ferromagnets into device architectures. This results in significant design complexities, especially in view of the rising demand for smaller and smaller transistors. A far better and practical way to manipulate the orientation of an electron's spin would be by using purely electrical means, like the switching on and off of an electrical voltage. This will be spintronics without ferromagnetism or all-electric spintronics, the holy grail of semiconductor spintronics."

The team used a device called a quantum point contact for their breakthrough. Debray said, "We used a quantum point contact — a short quantum wire — made from the semiconductor indium arsenide to generate strongly spin-polarized current by tuning the potential confinement of the wire by bias voltages of the gates that create it."

He continued saying, "The key condition for the success of the experiment is that the potential confinement of the wire must be asymmetric — the transverse opposite edges of the quantum point contact must be asymmetrical. This was achieved by tuning the gate voltages. This asymmetry allows the electrons — thanks to relativistic effects — to interact with their surroundings via spin-orbit coupling and be polarized. The coupling triggers the spin polarization and the Coulomb electron–electron interaction enhances it."

The team says that the next step in their research is to achieve the same results at higher temperatures using a different material like gallium arsenide.

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RE: Spintronics...uh???
By MrPoletski on 11/4/2009 10:19:47 AM , Rating: 2
I'll try to lamen-termsify it...

An electron has 'spin', in actual fact, every subatomic particle has spin it's just an electron is easier to work with.

What is 'spin'? imagine a snookerball. You can hit it with back/top spin (vertical axis) and you can hit it with left/right hand spin (horizontal axis). The 'spin' is the z component of this, difficult to visualise unless you start to think about the snookerball orbiting something. You can't 'spin' a ball so that it ends up moving around full circle that's unpossible (technical term). But we know that objects (like our moon around the earth) have a momentum associated with their orbit. The moon could have zero topspin and zero sidespin and still orbit around the earth.

In Quantum Mechanics, this z-component of angular momentum is normalised, so the 'spin' of the electron isn't in fact it's orbital angular momentum like I've been telling you, but the allowable values of its spin (electrons are allowed a spin of +1/2 or -1/2) designate what orbits the electrons are following. To get the actual momentum values would require further calculation, but would include the spin in the equation.

Spin is a property (like charge or colour), not a value (like speed or weight).

How is spin useful?

Spin is useful because the spin of an electron can be determined and modified. Immediately there you have 1 bit of memory whose maximum theoretical speed is limited only by that of the equipement you use to read or alter the spin.

What is this breakthrough?

Actually altering the spin of an electron is very difficult, now they have a technique that uses only electronics. It's kind of akin to the 'spintronics' field of science, like the rail industry, moving away from steam engines over to electric ones.

what they appear to be doing is creating an exact charge distribution that friggles the electron in such a way as to change the spin. It appears to do this by a cunningly designed charge distribution forcing the electron to move in a particular way. in getting it to move this way, the electron is interacting with its surroundings by a well documented quantum mechanical effect (spin ourbit coupling) and the spin is inverting.

So imagine the electron is a tennis ball and that this charge distribution is a bedsheet. A flat bedsheet has no charge. Poke a pencil up from underneath the bedsheet and you end up with a peak. This represents a negative charge, maximum at the pencil tip, reducing as you get further away (and the bedsheets get lower down and closer to the bed). Roll the tennis ball towards this peak and watch it deflect off the side of it.

now get several pencils and make a cool shape by poking them up under your bedsheet. Make a circle and make it badly. Your tennis ball cant roll up the sides of this ring, so its trapped. Keep rolling it around in circles inside this bedsheet bowl held up by pencils and you are almost there. When those pencils have their exact height under the bedsheet tuned exactly right (i.e. your charge dsitribution is correct), you can control the way the electron spins around inside your bowl. If you suddenly lifted one or two pencils high up, for example, you might be able to change the direction the ball is rolling in.

voila, you can control an electrons spin by manipulating electrical charges present in a system.

This is useful?
incredibly just not for some time (like most things). I have no doubt that this method, when refined, will make a huge difference to quantm computing to just mention one thing.

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