EPFL · Wetenschap

Graphene Device Measures Fractional Electron Charges

EPFL researchers have developed a novel graphene device capable of measuring the fractional electric charges of quasiparticles, which are emergent quantum objects formed by large numbers of electrons acting collectively under extreme conditions.

Under specific conditions known as the quantum Hall effect—where electrons are confined to two dimensions, subjected to intense magnetic fields, and cooled to very low temperatures—electrons cease to behave as individual particles. Instead, they organize into ordered quantum states, giving rise to quasiparticles that appear to carry only a fraction of an electron's fundamental charge.

The new device, constructed from bilayer graphene, utilizes an electrical gate to create a small energy barrier called an antidot. Quasiparticles travel around this antidot, and their tunneling events across the device at regular intervals generate electrical signal oscillations. By analyzing the spacing of these oscillations, researchers can determine the charge of the quasiparticles, effectively using the antidot as a sensitive charge meter.

Measurements using this device confirmed the presence of quasiparticles with charges of one-third of an electron's charge in several quantum Hall states (4/3, 5/3, and 7/3), as well as charges of two-thirds and three-fifths of an electron. The 8/3 state exhibited unusual behavior, showing signatures of both one-third and two-thirds electron charges, which the researchers are exploring through various explanations.

These fractionally charged quasiparticles are key characteristics of topological quantum matter and are crucial for testing fundamental quantum mechanics principles and understanding exotic states of matter. The compact, tunable graphene device offers a simpler and more practical method for studying these phenomena compared to previous complex experiments, with potential applications in future quantum technologies and the possibility of adaptation to other two-dimensional materials.

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