For more than half a century, physicists who study the flow of electrons have wondered how high conductance can go in a material. Conductance is the opposite of resistance; it describes how easily current passes through. Physicists study conductance to investigate fundamental properties of electrons. From a more practical standpoint, devices with high conductance make appealing components for future electronic devices.
The standard assumption, based on pioneering work from the 1960s, predicts a natural maximum for free electrons. Electrons lose momentum as they interact with the impurities, walls, and vibrations of the material, all sources of resistance. But even if they travel ballistically—unimpeded and without scattering—a quantum limit should apply. But new experiments have revealed streams of electrons flagrantly exceeding that upper bound as they flowed through tiny channels in a graphene device—not unlike water or gas streaming through a pinhole.
The work, led by physicist Andre Geim at the University of Manchester and with theoretical support from Marco Polini of Istituto Italiano di Tecnologia, in Genoa, reports the first experimental evidence of higher-than-expected conductance, with the electrons flowing like a fluid more viscous than honey. They describe the behavior as “superballistic” because it exceeds the limit for ballistic travel.
Finding such high conductance was “one of the big surprises in these experimental findings,” says physicist Kin Chung Fong at Harvard University, who was not involved in the study.
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