Decoding and controlling quantum materials with light
Dr. Hari Padma
Postdoctoral Fellow, Department of Physics
Harvard University
Describing quantum materials using effective models is key to understanding their behavior and rationally manipulating them. However, this approach can be challenging to apply in interacting many-body systems, as exemplified by the cuprate high-temperature superconductors. The cuprates exhibit strong electronic correlations, resulting in ordered phases that are intertwined across a complex phase diagram. While the Hubbard model has long been believed to capture the essential physics of these compounds, recent studies show that it fails to reproduce a homogeneous superconducting ground state. In this talk, I will describe how tailored electromagnetic fields allow us to reconstruct and then dynamically engineer the Hamiltonian describing the prototypical cuprate ladder Sr 14 Cu 24 O 41 . First, using resonant inelastic x-ray scattering, we observe that magnetic excitations from doped holes are strongly suppressed compared to the pure Hubbard model. Mapping our results to theoretical calculations, we find signatures of an enhanced hole pairing arising from a nearest-neighbor attractive interaction beyond the Hubbard model.
Next, I will illustrate how dressing the electronic Hamiltonian by intense optical fields enables the creation of a novel metastable nonequilibrium electronic state. Ultrafast terahertz and resonant x-ray spectroscopy reveal an optically-driven, long-lived segregation of holes, resulting in a nonequilibrium state with emergent plasmon-like collective excitations. The electronic metastability is induced by the optical activation of a hopping pathway that is otherwise forbidden by symmetry. Finally, I will discuss how light-matter interaction can reveal geometric properties of the Bloch wavefunction, towards the next frontier in the understanding and control of quantum materials.
Hosted by Prof. Ghimire