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 ). In this work, we use time-resolved x-ray absorption spectroscopy to demonstrate the light-induced renormalization of the Hubbard in a cuprate superconductor, . 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 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.
- Received 25 June 2021
- Revised 19 September 2021
- Accepted 9 November 2021
DOI:https://doi.org/10.1103/PhysRevX.12.011013
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
One of the most fundamental properties of atoms in a lattice is the energy cost of placing two electrons within a single orbital. This energy scale, known as the Hubbard , arises as a result of electric repulsion between like charges and crucially contributes to a wide variety of quantum phases of matter, from antiferromagnetism to high-temperature superconductivity. In most inorganic materials, the Hubbard is thought to be modified only by changing the basic chemical makeup of a substance, thus preventing its manipulation through external perturbations. Here, we experimentally demonstrate that the Hubbard of a high-temperature superconductor can be dynamically and reversibly altered by ultrashort laser pulses.
To probe changes in the Hubbard , we use time-resolved x-ray absorption spectroscopy, an established technique for monitoring modifications in the electronic structure of a material. While probing a high-temperature superconductor with ultrafast x rays, we simultaneously excite the sample with 50-fs pulses from an infrared laser. The x-ray absorption spectroscopy reveals a characteristic energy shift due to a change of the electronic structure and consistent with a lowering of the Hubbard —an effect akin to lowering the electric repulsion between electrons.
Our work paves the way for a novel strategy for the manipulation of emergent phases in light-driven quantum materials via dynamical engineering of the effective electronic interactions.
