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Imagine a highway with two lanes in each direction. One lane is for slow cars and the other is for fast cars. For electrons moving along a quantum wire, the Cambridge and Frankfurt researchers found that there are also two 'tracks,' but electrons can take both at the same time.
The current in a wire is carried by the flow of electrons. When the wire is very narrow (one-dimensional, 1D) then electrons cannot overtake each other, as they strongly repel each other. Current, or energy, is carried instead by waves of compression as one particle pushes on the next. It has long been known that there are two types of excitation for electrons, as in addition to their charge they have a property called spin. Spin and charge excitations travel at fixed, but different speeds, as predicted by the Tomonaga-Luttinger model many decades ago. However, theorists are unable to calculate what precisely happens beyond only small perturbations, as the interactions are too complex. The Cambridge team has measured these speeds as their energies are varied, and found that a very simple picture emerges (now published in the journal Science Advances). Each type of excitation can have low or high kinetic energy, like cars on a road, with the well-known formula E=1/2 mv2, which is a parabola. But for spin and charge the masses m 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. The results measure energy as a function of magnetic field, which is equivalent to momentum or speed v, showing these two energy parabolas, which can be seen in places all the way up to five times the highest energy occupied by electrons in the system. 'It's as if the cars (like charges) are travelling in the slow lane but their passengers (like spins) are going more quickly, in the fast lane', explained Pedro Vianez, who carried out the measurements for his PhD at the Cavendish Laboratory in Cambridge. 'Even when the cars and passengers slow down or speed up, they still remain separate!' 'What is remarkable here is that we are no longer talking about electrons but, instead, about composite (quasi)particles of spin and charge - commonly dubbed spinons and holons, respectively. For a long time, these were believed to become unstable at such high energies, yet what is observed points to exactly the opposite - they seem to behave in a way very 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!' said Oleksandr Tsyplyatyev, the theorist who led the work at the Goethe University in Frankfurt. (ANI)
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