A graphene device just directly measured particles carrying a third of an electron's charge

[DeanAmbrose]

Researchers have built a device that directly measures the fractional electric charge carried by some of the strangest objects in condensed matter physics, published in Nature Physics. An electron is supposed to be indivisible, carrying exactly one unit of charge, but under extreme conditions large numbers of electrons act collectively and give rise to quasiparticles that behave as if they carry only a fraction of that charge.

Those extreme conditions come from the quantum Hall effect, where electrons confined to two dimensions and exposed to an intense magnetic field at very low temperatures stop behaving like individual particles and organize into highly ordered collective states. The device itself is built from bilayer graphene, two sheets of carbon atoms, with electrical gates used to carve out a tiny energy hill called an antidot that quasiparticles move around in well defined paths.

Changing the magnetic field or gate voltage causes the quasiparticles to tunnel across the device at regular intervals, and each tunneling event produces a small oscillation in the electrical signal. By measuring the spacing between those oscillations, the researchers could work out the actual charge of the quasiparticles directly, essentially turning the antidot into an extremely sensitive charge meter.

The measurements revealed quasiparticles carrying one third of an electron's charge at several distinct quantum Hall states. Including states labeled 4/3, 5/3 and 7/3, along with quasiparticles carrying two thirds of an electron's charge at other states.

This kind of direct charge measurement matters because fractional quantum Hall states are a leading candidate platform for topological quantum computing. And precisely characterizing the actual quasiparticles involved, rather than just inferring their existence indirectly, is exactly the kind of foundational measurement that eventually determines whether a specific material platform is genuinely viable for building more complex devices on top of it

Graphene Device Fractional Electric Quantumphys.org