Effect of Berry connection on attosecond transient absorption spectroscopy in gapped graphene

TL;DR

This study explores how Berry connection influences attosecond transient absorption spectra in gapped graphene, revealing additional spectral components and providing analytical insights into the underlying mechanisms.

Contribution

The paper introduces a numerical and analytical investigation of Berry connection effects on ATAS in gapped graphene, highlighting new spectral features caused by symmetry breaking.

Findings

Gapped graphene exhibits an additional spectral oscillation at the pump frequency due to Berry connection.

Analytical model qualitatively reproduces numerical spectral features.

Spectral intensity depends on Berry connection and electron energy shifts at van Hove singularities.

Abstract

We investigate the attosecond transient absorption spectroscopy (ATAS) in gapped graphene by numerically solving the four-band density matrix equations. Our results reveal that, in contrast to pristine graphene, whose fishbone-shaped spectra oscillate at twice the pump laser frequency, the ATAS of gapped graphene exhibits an additional component oscillating at the pump laser frequency, induced by the Berry connection. To gain insight into these interesting results, we employ a simplified model to derive an analytical expression for the spectral component stemming from the Berry connection. Our analytical results qualitatively reproduce the key features observed in the numerical simulations, revealing that the intensity of the fundamental-frequency spectral component depends not only on the Berry connection but also on the energy shifts associated with the effective mass of electrons at the van Hove singularities. These results shed light on the complex generation mechanism of the ATAS in symmetry-broken materials.