2023 Fiscal Year Research-status Report
Nonlinear response of driven correlated materials
| Project/Area Number |
23K03300
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| Research Institution | Kyoto University |
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Principal Investigator |
Peters Robert 京都大学, 理学研究科, 講師 (80734293)
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| Project Period (FY) |
2023-04-01 – 2028-03-31
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| Keywords | nonlinear response / correlation effects / Edelstein effect / HHG / shift current / Rice-Mele model |
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| Outline of Annual Research Achievements |
The research on nonlinear phenomena in correlated materials advanced in two stages. On the one hand, we analyzed the nonlinear Edelstein effect in correlated materials using a perturbative technique. On the other hand, we made significant progress in analyzing responses with real-time evolution.
We developed a method to study the nonlinear spin response using single-particle Green's functions. Our analysis revealed that the nonlinear Edelstein effect can occur in centrosymmetric systems and that correlations enhance this effect. We also explored the optical version of the effect, i.e., the build-up of a static spin polarization in a time-dependent electric field, and we identified a delicate interplay between the lifetime of excitations and renormalization that can enhance or suppress the Edelstein effect. These results have been submitted to Phys. Rev. B.
Second, we studied the non-equilibrium dynamics of correlated systems and analyzed the response to an external electric field. Here, we perturbatively included fluctuations in the calculations using a correlation expansion. We demonstrated that for a noninteracting system, the Green's function technique mentioned above and the time evolution yield identical results. Then, we demonstrated in an interacting Rice-Mele model that the biexciton transition strongly enhances the response whenever the frequency of the incident light matches the exciton energy. These results have been published.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Due to very promising results, we focused more on the spin response in 2023 than on the nonlinear electric conductivity and the shift current. As described above, we made significant progress in the nonlinear Edelstein effect, exploring correlation effects on the static and optical versions of it.
Due to this, we have postponed the calculations of the second-order nonlinear conductivity in correlated Mott and Kondo insulators.
Furthermore, we also made some remarkable progress calculating the time evolution of correlated materials using the correlation expansion. Thus, we were able to calculate the nonlinear response in a correlated Rice Mele model based on time evolution. Due to this progress, we were also able to start comparing the response based on Green's function technique and the response calculated by the time evolution. Such calculations were initially planned to start in the second part of this project. Now, we were able to start this part early, which will open up new exciting possibilities in the future.
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| Strategy for Future Research Activity |
In 2024, we plan to shift our focus back to analyzing correlation effects on the second-order conductivity in strongly correlated insulators, such as Mott and Kondo insulators.
We plan to study the correlation effects on the second-order high-harmonic generation (HHG) and the shift current. Our investigation will focus on understanding the circumstances under which the interplay between correlations, band structure, and driving frequency generates a large shift current. In 2024, we also plan to calculate the nonlinear response of these correlated models in the ordered phases. We will focus on the Hubbard model and the periodic Anderson model, which also hosts several magnetic and superconducting phases. To study the nonlinear response of these phases, we will use the Green's function method.
Furthermore, we plan to advance our study of correlation effects using time evolution, including an external field. On the one hand, we want to use the correlation expansion. On the other hand, we recently made some progress in using neural network quantum states to simulate the time evolution of correlated systems. We thus will try to advance our calculation of the nonlinear response to an external field. After studying the interacting Rice-Mele model, we would try to study the Hubbard model using the correlation expansion or neural networks. This would allow us to analyze the impact of spin fluctuations on the nonlinear response.
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| Causes of Carryover |
During this fiscal year, we completed all planned activities, such as purchasing a computer and attending research workshops. However, there was a small amount of money remaining, which will be carried over to the next fiscal year.
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