Persistent coherence of quantum superpositions in an optimally doped cuprate revealed by 2D spectroscopy

TL;DR

This study uses 2D spectroscopy to reveal long-lasting quantum coherence in a cuprate superconductor, providing new insights into the interplay of excitations relevant to high-temperature superconductivity.

Contribution

First application of multidimensional coherent spectroscopy to a cuprate, uncovering persistent quantum coherence linked to electronic correlations in superconductors.

Findings

Quantum coherence persists for ~500 fs.

Coherence originates from superpositions of states separated by 20-60 meV.

Reveals correlation between high and low energy excitations.

Abstract

Understanding of the precise mechanisms of high-temperature superconductivity is elusive. In particular, in order to solve the puzzle of the pairing mechanism, it is important to understand the detailed nature of the excitations at energies around the superconducting gap. While measurements of the dynamics of excited electronic populations have been able to give some insight, they have largely neglected the intricate dynamics of quantum coherence. Here, we apply multidimensional coherent spectroscopy for the first time to a prototypical cuprate and report unprecedented coherent dynamics persisting for ~500 fs, originating directly from the quantum superposition of optically excited states separated by 20 - 60 meV. These results reveal the correlation between high and low energy excitations, and indicate that the interplay between many-body states on different energy scales conserves phase coherence. In revealing these dynamics we demonstrate that multidimensional coherent spectroscopy can address electronic correlations and interrogate many-body quantum systems in unprecedented ways.