セミナー案内

日時
6月 4日 (水), 13:30-
場所
Onsite (Room 413)
お問い合わせの際はtanaka.hiroto.54z[@]st.kyoto-u.ac.jp ([]を外す) までご連絡ください。
講演者
Mr. Hiroto Tanaka (Condensed Matter Theory Group)
タイトル
"Linear and Nonlinear Optical Responses in Topological Superconductors: Quantum Geometry and Collective Mode "
備考欄　（アブストラクト等）

Abstract:
 Optical measurements have revealed remarkable properties of superconductors. Recent progress in experimental techniques enables us to access nonlinear optical phenomena in superconductors. Nonlinear optics can detect the Higgs mode [1]. Another intriguing aspect of nonlinear optics is its close relation to quantum geometry in topological materials. The quantum geometric quantities, such as the Berry curvature and the quantum metric, give characteristic contributions to the superconducting nonlinear conductivities [2,3].
 Although the relationship between optical phenomena and the quantum-geometric properties has been focused on, the many-body effect on the quantum-geometric contribution to optical responses remains uncovered. In this study, we investigate the effects of collective modes on the linear and nonlinear optical responses in the promising platforms of topological superconductivity [4].We also explore the possibility of nonlinear responses to detect topological superconductivity. This study focuses on photocurrent conductivity. Our numerical results demonstrate the sign reversal of the photocurrent conductivity at the topological transition.
 To obtain the above results, we have developed a theoretical formulation of linear and nonlinear optical responses based on the Kadanoff-Baym method. Our formula leads to physically reasonable results of optical responses in a broad range of multiband superconductors. Optical responses would pave the way for investigating the interplay of quantum geometry and collective modes in superconductors.

References:
[1] R. Matsunaga et al., Science 345, 1145 (2014); R. Shimano and N. Tsuji, Annual Review of Condensed Matter Physics 11, 103 (2020).
[2] H. Watanabe et al., Phys. Rev. B 105, 024308 (2022).
[3] H. Tanaka et al., Phys. Rev. B 110, 014520 (2024).
[4] H. Tanaka and Y. Yanase, arXiv:2502.15373.