Dependency of quantum time scales on symmetry

TL;DR

This study measures quantum photoemission time delays in materials with different symmetries, revealing a strong dependence of attosecond time scales on the system's dimensionality and symmetry.

Contribution

It introduces an experimental approach linking quantum time delays to material symmetry, providing new insights into the role of symmetry in quantum time scales.

Findings

Quasi 2D materials show ~150 as delays.

Quasi 1D materials show >200 as delays.

3D Cu exhibits 26 as delay.

Abstract

Although used extensively in everyday life, time is one of the least understood quantities in physics, especially on the level of quantum mechanics. Here we use an experimental method based on spin- and angle-resolved photoemission spectroscopy from spin-degenerate dispersive states to determine the Eisenbud-Wigner-Smith (EWS) time delay of photoemission. This time scale of the quantum transition is measured for materials with different dimensionality and correlation strength. A direct link between the dimensionality, or rather the symmetry of the system, and the attosecond photoionisation time scale is found. The quasi 2-dimensional transition metal dichalcogenides 1T-TiSe$_2$ and 1T-TiTe$_2$ show time scales around 150 as, whereas in quasi 1-dimensional CuTe the photoionisation takes more than 200 as. This is in stark contrast with the 26 as found for 3-dimensional pure Cu. These results provide new insights into the role of symmetry in quantum time scales and may provide a route to understanding the role of time in quantum mechanics.