Abstract
Conventional superconductivity is caused by electron-phonon coupling. The discovery of high-temperature superconductors raised the question of whether such strong electron-phonon coupling is realized in cuprates. Strong coupling with some collective excitation mode has been indicated by a dispersion “kink”. However, there is intensive debate regarding whether the relevant coupling mode is a magnetic resonance mode or an oxygen buckling phonon mode. This ambiguity is a consequence of the energy of the main prominent kink. Here, we show a new landscape of dispersion kinks. We report that heavily overdoping a Bi2Sr2CaCu2O8+δ superconductor results in a decline of the conventional main kink and a rise of another sharp kink, along with substantial energy shifts of both. Notably, the latter kink can be ascribed only to an oxygen-breathing phonon. Hence, the multiple phonon branches provide a consistent account of our data set on the multiple kinks. Our results suggest that strong electron-phonon coupling and its dramatic change should be incorporated into or reconciled with scenarios for the evolution of high-Tc superconductivity.
Highlights
Conventional superconductivity is caused by electron-phonon coupling
Angle-resolved photoemission spectroscopy (ARPES) has served as a momentum-resolved probe of the coupling strength distribution, and it has been reported that the electronic dispersion of high-Tc cuprates usually has a prominent “kink” at around ω ~ 65 meV3–6
This has been ascribed to strong coupling with the bond-buckling B1g phonon of CuO2 planes[7,8,9,10,11] or the magnetic resonance mode detected by inelastic neutron scattering (INS)[12,13,14]
Summary
Conventional superconductivity is caused by electron-phonon coupling. The discovery of hightemperature superconductors raised the question of whether such strong electron-phonon coupling is realized in cuprates. Angle-resolved photoemission spectroscopy (ARPES) has served as a momentum-resolved probe of the coupling strength distribution, and it has been reported that the electronic dispersion of high-Tc cuprates usually has a prominent “kink” at around ω ~ 65 meV3–6 This has been ascribed to strong coupling with the bond-buckling B1g phonon of CuO2 planes[7,8,9,10,11] or the magnetic resonance mode detected by inelastic neutron scattering (INS)[12,13,14]. One can drastically reduce the magnitude of the superconducting gap without increasing the temperature[19, 20] This is ideal for studying the origin of the dispersion kink, because the kink energy depends on the boson frequencies and on the electronic excitation[8, 9]. We argue that a strong electron-phonon coupling is needed to explain the results
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