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Optical Distinguishability of Mott Insulators in Time vs Frequency Domain

High Harmonic Generation (HHG) promises to provide insight into ultrafast dynamics and has been at the forefront of attosecond physics since its discovery. One class of materials that demonstrate HHG are Mott insulators whose electronic properties are of great interest given their strongly-correlated nature. Here, we use the paradigmatic representation of Mott insulators, the half-filled Fermi-Hubbard model, to investigate the potential of using HHG response to distinguish these materials. We develop an analytical argument based on the Magnus expansion approximation to evolution by the Schrodinger equation that indicates decreased distinguishability of Mott insulators as lattice spacing, $a$, and the strength of the driving field, $F_0$, increase relative to the frequency, $ω_0$. This argument is then bolstered through numerical simulations of different systems and subsequent comparison of their responses in both the time and frequency domain. Ultimately, we demonstrate reduced resolution of Mott insulators in both domains when the dimensionless parameter $g \equiv aF_0 / ω_0$ is large, though the time domain provides higher distinguishability. Conductors are exempted from these trends, becoming much more distinguishable in the frequency domain at high $g$.