Abstract
We extend the first-principles analysis of attosecond transient absorption spectroscopy to two-dimensional materials. As an example of two-dimensional materials, we apply the analysis to monolayer hexagonal boron nitride (h-BN) and compute its transient optical properties under intense few-cycle infrared laser pulses. Nonadiabatic features are observed in the computed transient absorption spectra. To elucidate the microscopic origin of these features, we analyze the electronic structure of h-BN with density functional theory and investigate the dynamics of specific energy bands with a simple two-band model. Finally, we find that laser-induced intraband transitions play a significant role in the transient absorption even for the two-dimensional material and that the nonadiabatic features are induced by the dynamical Franz–Keldysh effect with an anomalous band dispersion.
Highlights
Attosecond transient absorption spectroscopy (ATAS) is a technique that employs attosecond laser pulses to probe modifications to the optical absorption in the time domain
Because its attosecond time-resolution is shorter than a typical time-scale of electron dynamics, which is on the order of femtosecond, it can naturally capture ultrafast electron dynamics in matter
Ab initio time-dependent density functional theory (TDDFT) simulations are a good candidate to analyze ATAS for 2D materials. To realize such simulation methods, we extend the TDDFT pump–probe simulation [31] of transient absorption spectroscopy to 2D materials
Summary
Attosecond transient absorption spectroscopy (ATAS) is a technique that employs attosecond laser pulses to probe modifications to the optical absorption in the time domain. ATAS has been further extended to solid-state materials to investigate rather complex electron dynamics in various phenomena such as band-gap renormalization [8], petahertz optical drive [9], dynamical. In order to fully understand such laser-induced ultrafast electron dynamics, ATAS is one of the most desirable experimental techniques as it can resolve the dynamics with natural time-resolution. To demonstrate the ab initio ATAS simulation, we employ monolayer h-BN as an example of a 2D material and investigate its transient optical property under intense infrared (IR) laser pulses. We analyze the obtained transient absorption spectra of h-BN with a 2D parabolic two-band model and clarify the microscopic mechanism of the ultrafast modification of the optical property.
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