Nonlinear Optical Spectroscopy of Nodal-Line Semimetals

TL;DR

This study explores how nonsymmorphic symmetry in 2D nodal-line semimetals influences their nonlinear optical responses, revealing unique harmonic generation mechanisms and polarization effects that could advance ultrafast photonic devices.

Contribution

It uncovers the fundamental role of nonsymmorphic symmetry in nonlinear optical phenomena of NLS, detailing polarization-dependent harmonic generation mechanisms and their potential applications.

Findings

Odd-order harmonics generated due to symmetry breaking.

Harmonics emitted parallel and perpendicular to laser polarization.

Distinct intrachain and interchain generation mechanisms.

Abstract

Intense laser-driven nonlinear optical phenomena in two-dimensional (2D) nodal-line semimetals (NLS) exhibit complex mechanisms, particularly in the NbSi$_{x}$Te$_{2}$ material systems characterized by nonsymmorphic symmetry-protected band degeneracy. Our findings reveal how nonsymmorphic symmetry-protected band degeneracy fundamentally influences the material's nonlienar optical responses. Notably, the nonsymmorphic glide-mirror symmetry leads to the exclusive generation of odd-order harmonics from inversion-symmetry-broken NLS. Moreover, harmonics are emitted parallel and perpendicular to the driving laser's polarization. We demonstrate distinct generation mechanisms arise from intrachain and interchain processes, with their relative contributions varying significantly with the polarization of the driving laser pulse. The polarization-dependence exhibits two-fold anisotropy, with each harmonic order showing characteristic angular distributions of maximum yield. Additionally, our analysis of the ellipticity-dependence reveals an intricate interplay between interband and intraband mechanisms. These insights open new possibilities for controlling harmonic generation through precise tuning parameters of the driving laser and highlight the potentials of NLS materials to fabricate lightwave-based photonics, optoelectronic and quantum devices operating on ultrafast timescales.