Engineering 101

Electrons Go Fast and Slow Simultaneously

For electrons moving along a quantum wire, researchers in Cambridge and Frankfurt have discovered that there are two ‘lanes’, and electrons can take both simultaneously!

The flow of electrons carries the current in a wire. If the wire is narrow, the electrons strongly repel each other. Current, or energy, is carried by waves of compression as one particle pushes on the next.

There are two types of excitations for electrons, as in addition to charge, they also have a property called spin. Spin and charge excitations travel at fixed but different speeds. Theorists cannot calculate what precisely happens beyond only small perturbations, as the interactions are too complex. The researchers measured these speeds and found that a very simple picture emerged. Each type of excitation can have low or high kinetic energy, but for spin and charge, the masses are different, and, since charges repel and so cannot occupy the same state as another charge, there is twice as wide a range of momentum for charge as for spin.

What is remarkable here is that we are no longer talking about electrons but (quasi)particles of spin and charge – commonly dubbed spinons and holons, respectively. For a long time, scientists believed they became unstable at such high energies; however, they seem to behave in a way similar to normal, free, stable electrons, each with their own mass, except that they are not, in fact, electrons, but excitations of a whole sea of charges or spins!

The research results open the question of whether this spin-charge separation of the whole electron sea remains robust beyond 1D, e.g., in high-temperature superconducting materials. It can be applied to logic devices that harness spin, which drastically reduces the energy consumption of a transistor, simultaneously improving our understanding of quantum matter and providing a new tool for engineering quantum materials.

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