Ultrafast lasers are an increasingly important tool to control and stabilize emergent phases in quantum materials. Among a variety of possible excitation protocols, a particularly intriguing route is the direct light engineering of microscopic electronic parameters, such as the electron hopping and the local Coulomb repulsion (Hubbard $U$). In this work, we use time-resolved x-ray absorption spectroscopy to demonstrate the light-induced renormalization of the Hubbard $U$ in a cuprate superconductor, ${\mathrm{La}}_{1.905}{\mathrm{Ba}}_{0.095}{\mathrm{CuO}}_4$. We show that intense femtosecond laser pulses induce a substantial redshift of the upper Hubbard band while leaving the Zhang-Rice singlet energy unaffected. By comparing the experimental data to time-dependent spectra of single- and three-band Hubbard models, we assign this effect to an approximately 140-meV reduction of the on-site Coulomb repulsion on the copper sites. Our demonstration of a dynamical Hubbard $U$ renormalization in a copper oxide paves the way to a novel strategy for the manipulation of superconductivity and magnetism as well as to the realization of other long-range-ordered phases in light-driven quantum materials.

中文翻译：

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铜酸盐超导体中现场库仑排斥的超快重整化

超快激光器是控制和稳定量子材料中出射相的日益重要的工具。在各种可能的激发方案中，一个特别有趣的途径是微观电子参数的直接光工程，例如电子跳跃和局部库仑排斥（哈伯德$ü$）。在这项工作中，我们使用时间分辨 X 射线吸收光谱来证明 Hubbard 的光诱导重整化$ü$ 在铜酸盐超导体中， ${拉}_{1.905}{巴}_{0.095}{\mathrm{氧化铜}}_4$. 我们表明，强烈的飞秒激光脉冲会引起上哈伯德波段的大量红移，同时不影响 Zhang-Rice 单重态能量。通过将实验数据与单波段和三波段 Hubbard 模型的时间相关光谱进行比较，我们将这种效应归因于铜位点上的现场库仑排斥减少了大约 140 meV。我们对动态哈伯德的演示$ü$ 氧化铜中的重整化为操纵超导和磁性的新策略以及在光驱动量子材料中实现其他长程有序相铺平了道路。