  High harmonic generation (HHG) spectra have the potential to show novel
signatures of ordered phases in condensed matter. We studied the femtosecond
laser-driven electronic response of monolayer NbSe2 using state-of-the-art
computational methods, which can guide future synthesis and optical
characterization. Earlier studies found distinct signatures of charge density
wave (CDW) ordered phases in the ground state of NbSe2 monolayers, in
co-existence with superconductivity. Driving such systems with ultrashort laser
pulses can shed new light on optically controlling various exotic phases (e.g.
CDW) in monolayer NbSe2. This will not only provide a fundamental understanding
of non-equilibrium phase-transitions in NbSe2, but also will open a path
forward for revolutionizing quantum information technologies, such as
valleytronics. To this end, we have studied high harmonic generation (HHG) in
monolayer NbSe2 under various optical pump intensities using real-time
time-dependent density functional theory (RT-TDDFT). Our calculations predict
distinct signatures in HHG spectra for certain harmonics in the presence of CDW
order in monolayer NbSe2. Finally, we also examined the dependence of HHG
spectra on excitation intensity and qualitatively revealed its power-law
behavior.
