Since the discovery of high transition-temperature superconductivity in cuprates, extensive studies have been done to elucidate unusual physical properties such as metal-insulator transition, pseudogap, and magnetic fluctuations [1–3]. To understand these unusual physical properties, it is crucial to clarify the roles of the entangled many-body interactions such as the electron-phonon interaction, electron-electron interaction, and electron-magnon (spin wave) interaction. The characteristics of these interactions are reflected in the functional form of the self-energy, Σ(k,ω;T) which is embedded in the high-resolution angle-resolved photoemission (ARPES) spectral shape. The major manifestation of the self-energy is the “kink structure” in the band dispersion, and energy-dependent linewidth broadening. In cuprate superconductors, two characteristic ARPES spectral features have been observed: the low-energy kink (LEK) around -80 meV and the high-energy anomaly (HEA) around -300 meV. By extracting the self-energy from the ARPES spectrum, one can clarify the many-body interactions that induce unusual physical properties of cuprate superconductors. However, the self-energy responsible for the LEK and HEA have not been consistently evaluated, and their origin and interrelationships have been elusive.
In this talk, we present temperature-dependent many-body interactions in heavily overdoped cuprate superconductor, Bi2201, using high-resolution ARPES. By developing a new analysis method based on the Kramers-Kronig transformation, we have successfully extracted self-energies corresponding to two distinct energy scales: the LEK and HEA. By comparing our experimental data with theoretical calculations, we found that the magnitude of the self-energy for the LEK significantly enhanced upon cooling while that for HEA was almost temperature-independent. The temperature dependence of self-energy for the LEK cannot be explained solely by the electron-phonon interaction, suggesting an unexplored enhancement mechanism emerging from entangled many-body interactions. On the other hand, the self-energy responsible for the HEA is assumed to originate from the strongly damped local excitations characterized by t (energy for charge transfer) or J (energy for magnetic interaction with neighboring sites).
[1] M. Imada et al., Rev. Mod. Phys. 70, 1039 (1986)
[2] M. Hashimoto et al., Nat. Phys. 10, 483-495 (2014)
[3] A. Kopp et al., Proc. Natl. Acad. Sci. 104, 6123 (2007)