Attosecond transient absorption spectroscopy in monolayer hexagonal boron nitride

TL;DR

This study uses simulations and analytical models to explore the attosecond transient absorption spectra of monolayer hexagonal boron nitride, revealing the roles of Berry connection and gap energy in spectral features.

Contribution

The paper introduces a simplified single-electron model at the M point to analytically explain the fishbone structure in ATAS of hBN, highlighting the influence of Berry connection.

Findings

The fishbone structure exhibits a temporal period matching the pump laser.

Both interband transition dipole moments and Berry connection influence the spectral features.

ATAS intensity increases with the gap energy, consistent with analytical predictions.

Abstract

We simulate the attosecond transient absorption spectroscopy (ATAS) of monolayer hexagonal boron nitride (hBN) using the time-dependent density functional theory and two-band density-matrix equations within the tight-binding approximation. The simulation results from the two methods are qualitatively consistent. We focus on the fishbone structure around the gap energy of the M point, which exhibits a temporal period equal to that of the pump laser. To gain deeper insight into this structure, we simplify the two-band model to a single-electron model located at the M point, allowing us to derive an analytical expression that can qualitatively reproduce the numerical results. By isolating the influence of the Berry connection on the ATAS, our analytical results reveal that both the interband transition dipole moments and the Berry connection play important roles in the fishbone structure of the ATAS. Moreover, we also have investigated the dependence of ATAS on the gap energy based the tight-binding approximation. The results demonstrate that the ATAS intensity is enhanced as the gap energy increases, in agreement with our analytical prediction. Our study may shed light on the generation mechanism of the fishbone structure of the ATAS in hBN.