Quantum electronics: Crucial twist?

Table of contents:

Quantum electronics: Crucial twist?
Quantum electronics: Crucial twist?

Crucial shoot?

Power on or power off - current computer models create entire (virtual) worlds with these two states. The electronics of the future should be more diverse and also take into account the torque of the electrons, their spin. But to do this, you first have to be able to distinguish between the particles according to their spin states. At school, it still looks so simple and literally "obvious": Two wires, a lamp, a battery - everything connected, and we schoolboys saw the light. If electricity can flow between plus and minus without any interference, it makes the glowing wire shine. And electricity - that was the next level of knowledge - is nothing more than a bunch of electrons, all of which are negatively electrically charged.

Happy if this knowledge is enough and since then you are no longer surprised when the uplighter actually provides pleasant reading light when you press the light switch. It's your own fault if you're curious to dig deeper and want to learn more about current flow and these dubious electrons. Because from now on it will only get more complicated, more diverse, more confused. But the unsteady mind didn't want it any other way.

So he learns that current flowing in a magnetic field not only creates light, but also experiences a force. Which means that the wandering electrons in the conductor are thrown off the straight path with gentle force. Instead of stubbornly going ahead, the wire also goes to the side. But because all electrons have the same negative charge, they all turn to the same side, which is why it's a bit overcrowded, while the opposite side is yawning emptiness. Too many electrons here, too few there - this results in a voltage that is called the Hall voltage after its discoverer Edwin Hall. It's not too big and is perpendicular to the direction of the current and the magnetic field, but it's clearly there and is even relatively easy to measure experimentally.

This may not seem too complicated. But we are still at the beginning. Next up are the electrons, which quantum physics reports are not only electrically charged, but also have an angular momentum, also known as spin. Graphically speaking, such a spin is very similar to the rotation of a globe in its holder: it either wobbles correctly from west to east or it rotates around its axis from east to west. If we disregard the fact that such an electron has to rotate twice through 360 degrees in order to have reached the initial state again (that's where the confusion begins), this analogy applies quite well. In any case, the spin of an electron points up or down.

If we now throw these two harmless additional pieces of knowledge together, then the Hall effect and electron spin result in something new that even seasoned physicists are currently having problems with: the spin Hall effect. For several decades it has been known - theoretically - that wandering electrons are also deflected by their spin properties. However, nobody can say exactly why this happens. Ideas range from scattering at imperfections in the conductor to this-is-an-internal-thing-of-the-electrons.

Anyone who does not shrug their shoulders and returns to the battery and the small lamp at this point is setting up heavy experimental setups in the laboratory in order firstly to find out whether this spin Hall effect also exists in experimental reality, and secondly to find out how, why and anyway. So did Sergio Valenzuela and Mike Tinkham from Harvard University. Two other groups before them had already demonstrated the predicted unequal distribution using optical methods, but Valenzuela and Tinkham wanted to capture the electrons in a manner befitting their status – electronically.

For this purpose, they made a nano-device that can only be properly recognized under an atomic force microscope. Essentially, this is an aluminum cross known in specialist circles as the Hall Cross. If a current flows from top to bottom, no voltage can be detected on the side arms, since the electron spins point up as often as down on average. It was therefore necessary to disturb this spin balance - which can be done particularly well with electrons from a material similar to iron, because such materials naturally contain more electrons with one spin direction. So the researchers placed a corresponding electrode across the top bar of the Hall cross and allowed spin-polarized electrons to tunnel into the cross over a barrier. Lo and behold: The asymmetry of the spins caused the expected electron migration and the hoped-for spin Hall voltage.

The measured value of ten billionths of a volt obtained by Valenzuela and Tinkham is quite small, but sufficient to use it in further experiments as an indicator of the spin Hall effect. For the near future, this means that equipped physicists will finally be able to delve even deeper into the mysteries of strange electrons. And on the horizon beckons the promising utopia of spintronics, in which information for new computers is no longer represented as banal on and off, but rather is contained in the spin properties. This is what can happen when you start harmlessly with wires, batteries and lamps and are still curious afterwards.

Popular topic