There are two lanes in each direction. There are two lanes for fast and slow cars. There are two lanes for electrons moving along a quantum wire, but they can take both at the same time.
The flow of electrons carries a current. electrons can't overtake each other if the wire is very narrow Waves of compression are used to carry current and energy.
There are two types of electrons that have a property called spin. The Tomonaga-Luttinger model predicted that spin and charge excitations would travel at different speeds. The interactions are too complex to be calculated by theorists. A very simple picture emerged from the Cambridge team's measurement of these speeds as their energies were varied. The well-known formula E is a parabola, which means that each type of excitation can have low or high energy levels. Since charges can't occupy the same state as another charge, there is twice as wide a range of momentum for charge as for spin. The two energy parabolas can be seen in places all the way up to five times the highest energy occupied by electrons.
Pedro Vianez, who carried out the measurements for his PhD at the Cavendish Laboratory in Cambridge, said that it was as if the cars were travelling in the slow lane but their passengers were in the fast lane. The cars and passengers are still separate even when they slow down.
We are no longer talking about electrons but about spin and charge particles called spinons and holons. For a long time, these were thought to be unstable, yet what is observed shows that they are just like normal, free, stable electrons.
Chris Ford, the leader of the experimental team, said the paper represents the culmination of over a decade of experimental and theoretical work on the physics of one-dimensional systems. We improved our measurement resolution to pick out new features when we took the system to higher energies. We fabricated a series of wires ranging from 1 to 18 microns in length, which is down to a thousandth of the millimeter, with as few as 30 electrons in a wire, and measured them at 0.3 K.
There are details on experimental techniques.
A map of the relation between energy and momentum can be created by the tunneling of electrons from the 1D wires into an adjacent electron gas. A commonly used method for determining the band structure of materials is angle-resolved photoemission spectroscopy. Vianez said that the system is buried 100 nanometers below the surface. The researchers were able to achieve resolution and control in this experiment.
It was the conclusion.
The question of whether the spin-charge separation of the whole electron sea remains robust beyond 1D has been raised. It may be applied to logic devices that harness spin, which offers a drastic reduction in the energy consumption of a transistor, as well as improving our understanding of quantum matter.
More information: Pedro M. T. Vianez et al, Observing separate spin and charge Fermi seas in a strongly correlated one-dimensional conductor, Science Advances (2022). DOI: 10.1126/sciadv.abm2781 Journal information: Science Advances
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