1. multipoint correlation functions: spectral representation and numerical evaluation

Seung-Sup B. Lee

Ludwig Maximilian University of Munich, Germany

12 August 2021 Thu 4 pm

                                      IBS Center for Theoretical Physics of Complex Systems (PCS), Administrative Office (B349), Theory Wing, 3rd floor

                                      Expo-ro 55, Yuseong-gu, Daejeon, South Korea, 34126 Tel: +82-42-878-8633                     

Four-point correlation functions on the real-frequency axis describe experimentally relevant properties, such as nonlocal susceptibilities, transport, and inelastic photon scattering, of the systems of interacting quantum particles. However, the non-perturbative computation of real-frequency multipoint functions has been intractable. In this talk, I will summarize our recently developed method for non-perturbatively computing multipoint functions and its applications [1, 2]. We have derived generalized spectral representations for multipoint functions that apply in all of the commonly used many-body frameworks [1]: the imaginary-frequency Matsubara and the real-frequency zero-temperature and Keldysh formalisms. We have developed a numerical renormalization group (NRG) method for evaluating the spectral representations for local multipoint functions, which can treat temperatures and frequencies---imaginary or real---of all magnitudes, from large to arbitrarily small ones [2]. I will present the numerical results of four-point vertex functions and resonant inelastic x-ray scattering (RIXS) spectra of quantum impurity systems.

[1] F. B. Kugler*, S.-S. B. Lee*, and J. von Delft, arXiv:2101.00707, Accepted in Phys. Rev. X.

[2] S.-S. B. Lee*, F. B. Kugler, and J. von Delft, arXiv:2101.00708, Accepted in Phys. Rev. X.

*: (co-)first authors.