Ultrafast renormalization of the onsite Coulomb repulsion in a cuprate superconductor

TL;DR

This study demonstrates that intense ultrafast laser pulses can dynamically reduce the onsite Coulomb repulsion in a cuprate superconductor, offering a new method to control electronic phases in quantum materials.

Contribution

It provides the first experimental evidence of light-induced renormalization of the Hubbard U in a cuprate superconductor using time-resolved x-ray absorption spectroscopy.

Findings

Ultrafast lasers cause a redshift of the upper Hubbard band.

The Coulomb repulsion U is reduced by approximately 140 meV.

The Zhang-Rice singlet energy remains unaffected.

Abstract

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, La$_{1.905}$Ba$_{0.095}$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 a $\sim140$ meV reduction of the onsite 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, magnetism, as well as to the realization of other long-range-ordered phases in light-driven quantum materials.