Experts demonstrated a situation, previously only theoretically predicted, in which electrons flow through a superconductor like water through a tube. As a working group led by Hong Yue Yang of Boston College reported in Nature Communications,, the strange fluid is created when the electrons react vigorously to the lattice vibrations of the material and recover all the energy given to them. Under these conditions they form a liquid with oscillation quanta known as phonons. This means that the electrons are no longer moving as individual particles, but in a common state described by the hydrodynamic equations.
So far, proof of the expected existence of the liquid has failed because none of the superconducting materials had the necessary combination of properties. In order for electrons and phonons to couple to each other, some other interaction, for example inter-electron scattering processes, must be very small. This is NbGe in the examined material2 the case. Under these conditions, something strange happens: although the electrons continue to transfer their momentum to the phonons of the lattice vibrations during the scattering processes, they, in turn, are scattered by the electrons and transfer the momentum back. As a result, momentum rotates between electrons and phonons without losses, and instead of the movement of individual particles determined by scattering and diffusion, one observes a flowing substance.
Yang’s team demonstrated the existence of the strange fluid based on three variations of classical superconductors. On the other hand, the effective mass of electrons turned out to be three times higher than expected, and this is due to the fact that phonons contribute to the mass thanks to the coupling; On the other hand, the electrical properties of the material have changed. Finally, infrared scattering experiments show that the material vibrates differently than one would expect in the case of classical superconductivity. This is a consequence of the hydrodynamic behavior of electrons, which is fundamentally different from the classical motion of scattered particles. The working group now wants to examine whether the superconductor behaves differently when it is a few nanometers in diameter – which is comparable to water flowing through an increasingly narrow tube.
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