Nonperturbative effects in second harmonic generation
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arXiv
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| Format: | Preprint |
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2026
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| _version_ | 1866915920515956736 |
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| author | Kitayama, Keisuke Ogata, Masao |
| author_facet | Kitayama, Keisuke Ogata, Masao |
| contents | Second-harmonic generation (SHG) is a quintessential probe of inversion symmetry breaking in condensed matter. While perturbative $χ^{(2)}$ processes are well-documented, the nonperturbative regime under intense driving remains largely unexplored. In this Letter, we develop a nonperturbative Floquet-Keldysh theory to describe SHG in two-band systems. Our analysis reveals the emergence of two distinct types of nonperturbative saturation: a transition from the conventional $E^2$ scaling to a linear $E$ dependence, and a stronger saturation regime where the SHG response becomes independent of the field amplitude. These behaviors are analytically shown to be governed by one-photon and two-photon resonance processes, respectively. By applying our formalism to a tight-binding model of monolayer GeS, we demonstrate that these specific scaling behaviors are observable in realistic materials and are fully consistent with large-scale numerical Floquet-matrix calculations. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2604_05710 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Nonperturbative effects in second harmonic generation Kitayama, Keisuke Ogata, Masao Strongly Correlated Electrons Mesoscale and Nanoscale Physics Second-harmonic generation (SHG) is a quintessential probe of inversion symmetry breaking in condensed matter. While perturbative $χ^{(2)}$ processes are well-documented, the nonperturbative regime under intense driving remains largely unexplored. In this Letter, we develop a nonperturbative Floquet-Keldysh theory to describe SHG in two-band systems. Our analysis reveals the emergence of two distinct types of nonperturbative saturation: a transition from the conventional $E^2$ scaling to a linear $E$ dependence, and a stronger saturation regime where the SHG response becomes independent of the field amplitude. These behaviors are analytically shown to be governed by one-photon and two-photon resonance processes, respectively. By applying our formalism to a tight-binding model of monolayer GeS, we demonstrate that these specific scaling behaviors are observable in realistic materials and are fully consistent with large-scale numerical Floquet-matrix calculations. |
| title | Nonperturbative effects in second harmonic generation |
| topic | Strongly Correlated Electrons Mesoscale and Nanoscale Physics |
| url | https://arxiv.org/abs/2604.05710 |