For the first time, quantum physicists at Delft University of Technology have shown the possibility of controlling and manipulating spin waves on a chip using superconductors. This breakthrough will not only give new insight into the interaction between magnets and superconductors, but the tiny waves in magnets could also offer an alternative to electronics in the future.
Controlling Spin Waves With Superconductors
Spin waves refer to the waves in a magnetic material which can be used in transmitting information. Since spin waves have the potential to be a building block for an energy-efficient replacement for electronics, experts have been searching for an efficient way of controlling them for years.
By theory, it is predicted that metal electrodes give control over spin waves, but scientists have barely seen such efforts in experiments until now. Led by Michael Borst, the research team at Delft University of Technology has proven that they can control spin waves properly if a superconducting electrode is used.
The researchers used a thin magnetic layer of yttrium iron magnet (YIG) which is known as the best magnet on Earth. On top of that, they laid a superconducting electrode and other electrodes to induce the spin waves. The electrode was turned into a superconducting state by cooling it to -268 degrees.
The spin waves were imaged by measuring their magnetic field using a unique sensor made from electrons in diamond. This imaging technique enables them to look through the opaque superconductor at the spin waves underneath, in the same way that an MRI scanner can look through the skin into someone's body.
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Useful Applications of Spin Wave Manipulation
A spin wave generates a magnetic field which generates a supercurrent in the superconductor. This supercurrent serves as a mirror for the spin wave, with the superconducting electrode reflecting the magnetic field back to the spin wave. The superconducting mirror causes the spin waves to move up and down more slowly, making the waves easily controllable.
According to Borst, it was found that the wavelength of the spin waves changes completely when they pass under the superconducting electrode. They can even tune the magnitude of the change very accurately by varying the temperature of the electrode slightly.
For the scientists, it was an amazing sight to see the spin waves getting slower and slower as the electrode gets colder. This gave the researchers a unique handle to manipulate the spin waves, allowing them to deflect and reflect the spin waves and make them resonate.
As described by Borst, spin wave technology is still in its infancy. For instance, using this breakthrough to make energy-efficient computers requires building small circuits to perform calculations. The discovery made by the researchers opens a door by allowing countless new and energy-efficient spin-wave circuits.
It is now possible to design devices on spin waves and superconductors that generate little heat and sound waves. This can be thought of as the spintronics version of frequency filters or resonators where the components can be found in electronic circuits of cell phones. They can also be seen as circuits that can serve as transistors or connectors between qubits in a quantum computer.
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