Impact of a Fano resonance on the measured transition time scale in solid state photoemission

TL;DR

This study investigates how a Fano resonance affects the measurement of quantum transition time scales in solid-state photoemission, revealing significant deviations from traditional models near resonance conditions.

Contribution

It demonstrates that Fano resonances alter the spin polarization signals used to measure transition times, challenging existing semi-analytical models and highlighting the need for resonance-specific information.

Findings

Spin polarization sign reversal near Fano resonance

Significant decrease in measured transition time

Breakdown of conventional models at resonance

Abstract

Fundamental quantum transition time scales are accessible through the spin polarization of photoelectrons coming from initially spin-degenerate states for solid-state materials . In this work we investigate the modification of this time scale in the vicinity of a Fano resonance in photoemission from a solid. We employ spin- and angle-resolved photoemission spectroscopy (SARPES) to study the valence band of 1T-TiSe$_2$ and 1T-TiTe$_2$, with an excitation photon energy coinciding with the Ti 3p-3d autoionization state. The energy derivative of the measured spin polarization, which is in the off-resonance case proportional to the transition time, reveals a sign reversal and significant magnitude decrease compared to off-resonance measurements. We show that this effect goes beyond conventional semi-analytical models used to translate spin polarization to the EWS time delay. At the Fano resonance, the underlying interference assumption of the model breaks down, and additional information about resonance strength is needed to extract the transition time delays.