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Publisher: [London] : Nature Publishing Group × Subject: Magnetic properties and materials ×

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    High-energy magnetic excitations from heavy quasiparticles in CeCu2Si2
    ([London] : Nature Publishing Group, 2021) Song, Yu; Wang, Weiyi; Cao, Chongde; Yamani, Zahra; Xu, Yuanji; Sheng, Yutao; Löser, Wolfgang; Qiu, Yiming; Yang, Yi-feng; Birgeneau, Robert J.; Dai, Pengcheng
    Magnetic fluctuations is the leading candidate for pairing in cuprate, iron-based, and heavy fermion superconductors. This view is challenged by the recent discovery of nodeless superconductivity in CeCu2Si2, and calls for a detailed understanding of the corresponding magnetic fluctuations. Here, we mapped out the magnetic excitations in superconducting (S-type) CeCu2Si2 using inelastic neutron scattering, finding a strongly asymmetric dispersion for E ≲ 1.5 meV, which at higher energies evolves into broad columnar magnetic excitations that extend to E ≳ 5 meV. While low-energy magnetic excitations exhibit marked three-dimensional characteristics, the high-energy magnetic excitations in CeCu2Si2 are almost two-dimensional, reminiscent of paramagnons found in cuprate and iron-based superconductors. By comparing our experimental findings with calculations in the random-phase approximation,we find that the magnetic excitations in CeCu2Si2 arise from quasiparticles associated with its heavy electron band, which are also responsible for superconductivity. Our results provide a basis for understanding magnetism and superconductivity in CeCu2Si2, and demonstrate the utility of neutron scattering in probing band renormalization in heavy fermion metals.
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    Observation of the sliding phason mode of the incommensurate magnetic texture in Fe/Ir(111)
    ([London] : Nature Publishing Group, 2024) Yang, Hung-Hsiang; Desplat, Louise; Kravchuk, Volodymyr P.; Hervé, Marie; Balashov, Timofey; Gerber, Simon; Garst, Markus; Dupé, Bertrand; Wulfhekel, Wulf
    The nanoscopic magnetic texture forming in a monolayer of iron on the (111) surface of iridium, Fe/Ir(111), is spatially modulated and uniaxially incommensurate with respect to the crystallographic periodicities. As a consequence, a low-energy magnetic excitation is expected that corresponds to the sliding of the texture along the incommensurate direction, i.e., a phason mode, which we explicitly confirm with atomistic spin simulations. Using scanning tunneling microscopy (STM), we succeed to observe this phason mode experimentally. It can be excited by the STM tip, which leads to a random telegraph noise in the tunneling current that we attribute to the presence of two minima in the phason potential due to the presence of disorder in our sample. This provides the prospect of a floating phase in cleaner samples and, potentially, a commensurate-incommensurate transition as a function of external control parameters.