Electrons take the fast and slow lanes at the same time

Electrons take the fast and slow lanes at the same time

Figure 1. A parabola for spin (in green) and charge excitation (purple). The inset shows the charging line in more detail. Credit: Research Team, Cavendish Laboratory, Department of Physics, University of Cambridge

Imagine a road with two lanes in each direction. One is for slow cars and the other for fast cars. For electrons moving along a quantum wire, researchers in Cambridge and Frankfurt have discovered that there are also two “lanes”, but electrons can take both at the same time!

The current in the wire is transmitted by the flow of electrons. When the wire is too narrow (one-dimensional, 1D), the electrons cannot outpace each other, because they repel each other strongly. The current, or energy, is instead transferred by compression waves as one particle pushes on the next.

It has long been known that there are two types of excitation of electrons, in addition to their charge, they have a property called yarn. The excitation of spin and charge travel at constant, but different speeds, as the Tomonaga-Luttinger model predicted several decades ago. However, theorists are unable to accurately calculate what happens after only small perturbations, because the interactions are so complex. The Cambridge team measured these speeds due to their varying energies, and found that a very simple image (now published in the journal) shows science progress). Each type of excitation can have low or high kinetic energy, such as cars on the road, with the known formula E = 1/2 mv2, which is a parabola. But for fans to spin and charge M different, and since charges repel each other and therefore cannot occupy the same state as another charge, the momentum range of a charge is twice that of a charge’s momentum compared to spin. The results measure energy as a function of the magnetic field, which is equivalent to momentum or velocity Fifthwhich shows these two energy parabolas, which can be seen in places along the way up to five times the highest energy occupied by the electrons in the system.

Electrons take the fast and slow lanes at the same time

Figure 2. Turn (green) and charge (holon, purple) excitation in a one-dimensional wire. Credit: Research Team, Cavendish Laboratory, Department of Physics, University of Cambridge

“It’s as if cars (like cargo) are going in the slow lane, but their passengers (like turning) are going faster, in the fast lane,” explained Pedro Vianez, who took the measurements for his Ph.D. At the Cavendish Laboratory in Cambridge. “Even when cars and passengers slow down or speed up, they stay separate!”

“What is remarkable here is that we are no longer talking about electrons but, instead, about (semi) complex particles of spin and charge – commonly called spinons and holons, respectively. For a long time, it was thought that they became unstable at such energies High, however, what was observed indicates the exact opposite – they seem to behave in a very similar way to normal, free and stable electrons, each with their own mass, except that they are not actually electrons, but are actually excitations of a whole sea of ​​charges or spins!” Oleksandr said. Tsiblatiev, the theorist who led the work at Goethe University in Frankfurt.

“This paper represents the culmination of more than a decade of experimental and theoretical work in the physics of one-dimensional systems,” said Chris Ford, who led the experimental team. “We were always curious to see what would happen if we took the system to higher energies, so we gradually improved the measurement accuracy to choose new features. We made a series of semiconductor arrays from wires ranging from 1 to 18 microns in length (that is, down to a thousandth of a millimeter or about 100 times thinner than a human hair), with less than 30 Electrons in a wire, measured at 0.3 K (or in other words, -272.85 C, ten times colder than Outer Space). “

Electrons take the fast and slow lanes at the same time

Figure 3a. Scanning electron micrographs of a device, showing the different gates used to identify 1D wires (Part 1). Credit: Research Team, Cavendish Laboratory, Department of Physics, University of Cambridge

Details of the experimental technique

Electrons are spent from the 1D wires into a neighboring 2D electron gas, which acts as a spectrometer, producing a map of the relationship between energy and momentum. “This technique is very similar to the angle solving method in all respects photoemission spectroscopy (ARPES), a commonly used method for determining the band structure of materials in condensed matter physics. The main difference, Vianez said, is that, instead of probing the surface, our system is buried a hundred nanometers beneath it,” allowing the researchers to achieve unprecedented precision and control for this type of spectroscopy experiment.

Electrons take the fast and slow lanes at the same time

Figure 3b. Scanning electron micrographs of a device, showing the different gates used to identify 1D wires (part 2). Credit: Research Team, Cavendish Laboratory, Department of Physics, University of Cambridge

conclusion

These results now open the question whether the spin charge separation of the entire electron sea remains strong beyond 1D, for example, in high-temperature superconducting materials. It can also now be applied to spin-harness logic devices (spintronics), which provide a drastic reduction (by three orders of magnitude!) energy consumption of the transistor, which at the same time improves our understanding of quantum matter as well as offering a new tool for engineering quantum materials.


A quantum simulator shows how bits of electrons move at different speeds in 1D


more information:
Pedro MT Vianez et al, Observation of discrete spin and charge in the Fermi seas in a highly interconnected one-dimensional conductor, science progress (2022). DOI: 10.1126 / sciadv.abm2781

Introduction of
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