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Fractional charge carriers make some noise with photons!

Researchers from CEA-Iramis have designed a new experimental method using microwave photons that brings additional proof that the electrical charge of carriers may amount to a third or a fifth of the elementary charge of the electron. Moreover, the experiment shows that these fractionally charged carriers (called "anyons") interact with microwave photons and can therefore be manipulated. This discovery is the first step towards the study of anyons' quantum and statistical properties.
Published on 29 April 2019

The electron is an elementary particle, with an elementary electrical charge that is, a priori indivisible.

However, in 1997, the Iramis team proved for the first time the existence of fractional electrical charges, in a two-dimensional conductor subjected to an intense magnetic field. This result came after the basic discovery, in 1980, of the fractional quantum Hall effect. These fractional charge carriers, which can only live in the conductor but not in free space, were named "anyons" because they displayed a different behavior from fermions (electrons) and bosons (photons): any-ons!

To proceed, the Iramis researchers have detected and analyzed the very tiny "noise" (fluctuations) of a very weak electrical current. Indeed, for a strong electrical current, the noise level is proportional to the current's strength, but it is different for a very weak current at a very low temperature. The charges are carried individually and the "noise" can give us information like the granularity of the charge. It is as if listening to the rain could tell us about the size of the drops…

More practically, the researchers studied a monolayer of electrons confined at the interface of two semi-conducting layers (GaAs and AIGaAs). This two-dimensional conductor was placed in a strong  magnetic field of about ten teslas and at a temperature of 20 millikelvins. They designed a circuit that allowed the electrical charges to flow one by one, and they recorded their movements over time. They analyzed the fluctuations they observed and deduced the value of the carried charges: e/3.

Today the team showed that it was possible to manipulate these anyons using photons. To that end, they used the same experiment as before, but added a microwave field over the DC (direct current) voltage applied to the circuit. These microwave photons induce an extra noise above a particular DC voltage whose value is directly linked to the fractional charge. Not only does this experiment corroborates and strengthens the results published in 1997 thanks to the observation of the e/5 fraction, but it also demonstrates the anyons' capacity to absorb or emit microwave photons.

The discovery of this interaction has several consequences. It is now possible to create and manipulate anyons at will, which opens up a whole new field of study regarding their properties. Since they are neither fermions nor bosons, what quantum statistics do these particles obey? We now have the tools to answer this very basic question.

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