Attosecond All-Optical Retrieval of Valley Polarization via Circular Dichroism in Transient Absorption

TL;DR

This paper introduces an attosecond optical method using circular dichroism in transient absorption to directly and quantitatively measure ultrafast valley polarization dynamics in 2D materials with subfemtosecond precision.

Contribution

It presents a novel all-optical scheme for real-time retrieval of valley polarization dynamics in 2D materials using attosecond circular dichroism spectroscopy, supported by ab initio calculations.

Findings

Successfully demonstrated the scheme for h-BN and MoS2.

Achieved subfemtosecond time resolution in measuring valley polarization.

Enabled quantitative tracking of transient valley polarization switching.

Abstract

We propose a scheme for retrieving the ultrafast valley polarization (VP) dynamics in two-dimensional hexagonal materials via attosecond circular dichroism (CD) transient absorption spectroscopy. This approach builds on the CD transition between the first and higher conduction bands induced by the circularly polarized probe pulses. The population imbalance at nonequivalent valleys in the first conduction band is proportionally mapped onto the difference in absorption coefficients of two probe pulses with opposite helicities, supporting an unprecedented quantitative retrieval of the corresponding VP dynamics with subfemtosecond time resolution. We theoretically demonstrate the scheme for h-BN and MoS2 through ab initio calculations, achieving an accurate retrieval of the VP dynamics, particularly the transient VP switching processes, with a time resolution of 250 as.