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    訪客 2021/07/14 16:26

    CUA Virtual Seminar – Polaron physics from the perspective of collective modes in one and two spatial dimension
    Pavel Dolgirev

    The Fermi-polaron problem of a mobile impurity interacting with fermionic medium emerges in various contexts, ranging from the foundations of Landau’s Fermi-liquid theory to electron-exciton interaction in semiconductors, to unusual properties of high-temperature superconductors. While classically the medium provides only a dissipative environment to the impurity, quantum picture of polaronic dressing is more intricate and arises from the interplay of few- and many-body aspects of the problem. The conventional expectation for the dynamics of Fermi polarons is that it is dissipative in character, and any excess energy is rapidly emitted away from the impurity as particle-hole excitations. Here we report a strikingly different type of polaron dynamics in a one-dimensional system of the impurity interacting repulsively with the fermions. When the total momentum of the system equals the Fermi momentum, there emerges a sharp collective mode corresponding to long-lived oscillations of the polaronic cloud surrounding the impurity. This mode can be observed experimentally with ultracold atoms using Ramsey interferometry and radio-frequency spectroscopy. Time allows, I will touch also polarons in two spatial dimensions in the context of excitons immersed into a sea of strongly interacting electrons in a magnetic field. It is the collective modes of the fermionic ground state, such as integer Quantum Hall states or Wigner crystal state, that determine exciton spectral properties.