Correlation-induced phase shifts and time delays in resonance enhanced high harmonic generation from Cr+

TL;DR

This study explores resonance-enhanced high harmonic generation in Cr+ using various models, revealing electron correlation effects and a significant time delay linked to resonance dynamics, advancing ultrafast spectroscopy understanding.

Contribution

It demonstrates that electron correlations are crucial for rHHG and uncovers a correlation-induced 480-attosecond delay, challenging previous models and interpretations.

Findings

TDDFT reveals spin-down 3p states dominate rHHG

Electron correlations are essential for accurate rHHG modeling

A ~480 attosecond delay is induced by electron correlation

Abstract

We investigate resonance-enhanced high harmonic generation (rHHG) in Cr+ by comparing a 1D shape-resonant model, time-dependent density functional theory (TDDFT), and independent particle approximation (IPA) simulations. Previous studies linked rHHG to the 3p -> 3d giant resonance, suggesting a modified four-step model where recolliding electrons are first captured in the autoionizing state before recombining into the ground state, potentially leading to an emission delay associated with the resonance lifetime. While both the 1D-model and TDDFT reproduce experimental spectra, TDDFT reveals that rHHG counterintuitively originates from spin-down 3p states, while spin-up 3d electrons negligibly contribute. The IPA fails to reproduce rHHG, highlighting the significance of electron correlations. Furthermore, TDDFT revealed a correlation induced ~480 attosecond time delay, accompanied by a strong phase shift across the resonance, potentially explaining earlier RABBIT measurements. Our work sheds light on long-standing open questions in rHHG and should advance novel ultrafast spectroscopies of electron correlations and resonances.