Anomalous spin dynamics after dual optical excitation

TL;DR

This paper shows that dual femtosecond optical pulses can fundamentally alter electron spin dynamics in copper, leading to longer spin imbalance decay times and challenging existing models of ultrafast light-matter interactions.

Contribution

It demonstrates that dual optical excitation can transiently modify electron dynamics beyond simple energy level occupancy changes, opening new possibilities for ultrafast spin control.

Findings

~2.5-fold increase in spin imbalance decay time with dual pulses

Dual excitation affects angular momentum transfer efficiency

Challenges conventional ultrafast light-matter interaction models

Abstract

Ultrashort optical pulses are a cornerstone for manipulating electronic and magnetic states in materials on a femtosecond timescale. Conventional models assume that optical excitation primarily modifies the occupation of the electron energy levels without long-lasting altering of the coupling of individual electrons in certain processes. Here, we demonstrate that optical excitation with two femtosecond pulses that come from different directions fundamentally transforms the electron dynamics in copper, affecting the efficiency of angular momentum transfer between electrons and the lattice. Using time-resolved magneto-optical Kerr effect measurements, we reveal a ~2.5. increase in spin imbalance decay time following inverse Faraday effect excitation under dual-pump conditions compared to single-pulse excitation. This observation challenges the prevailing paradigm of ultrafast light-matter interactions, showing that dual optical excitation can transiently modify electron dynamics beyond simple changes in the energy levels occupancy. Our findings open new avenues for controlling quantum states through a dual pump approach, with implications for ultrafast spintronics and the design of novel light-driven states.