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arXiv · 2105.00387

High-energy magnetic excitations from heavy quasiparticles in CeCu$_2$Si$_2$

Yu Song·Weiyi Wang·Chongde Cao·Zahra Yamani·Yuanji Xu·Yutao Sheng·Wolfgang Löser·Yiming Qiu·Yi-feng Yang·Robert J. Birgeneau·Pengcheng Dai
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Abstract

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 CeCu$_2$Si$_2$, and calls for a detailed understanding of the corresponding magnetic fluctuations. Here, we mapped out the magnetic excitations in \ys{superconducting (S-type)} CeCu$_2$Si$_2$ using inelastic neutron scattering, finding a strongly asymmetric dispersion for $E\lesssim1.5$~meV, which at higher energies evolve into broad columnar magnetic excitations that extend to $E\gtrsim 5$ meV. While low-energy magnetic excitations exhibit marked three-dimensional characteristics, the high-energy magnetic excitations in CeCu$_2$Si$_2$ 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 CeCu$_2$Si$_2$ 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 CeCu$_2$Si$_2$, and demonstrate the utility of neutron scattering in probing band renormalization in heavy fermion metals.

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Yu Song, Weiyi Wang, Chongde Cao, Zahra Yamani, Yuanji Xu, Yutao Sheng, Wolfgang Löser, Yiming Qiu, Yi-feng Yang, Robert J. Birgeneau, Pengcheng Dai. 2021-05-02. High-energy magnetic excitations from heavy quasiparticles in CeCu$_2$Si$_2$. https://doi.org/10.1038/s41535-021-00358-x

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