Effect of charge excitations and electron-phonon coupling on the robust superconductivity in tri-layer cuprate Bi2Sr2Ca2Cu3O10+x

The superconductivity in tri-layer cuprate Bi2Sr2Ca2Cu3O10+x (Bi2223) is intriguing, not only because it has the highest Tc,max (~110K) among Bi-family, but also the Tc shows a negligible reduction with overdoping. This is very surprising since this obviously violates the Tc dome that is deemed a universal trend for cuprates. However, there is still no consensus on why the Tc is so robust in the overdoped Bi2223. Here we propose to use the high resolution resonant inelastic X-ray scattering (RIXS) to examine the T-dependence of charge excitations and electron-phonon coupling (EPC) in optimally and overdoped Bi2223, which are reported to entangle with the superconducting phase of cuprates. The aim is to determine their correlations with the robust high Tc and find out the essential factor for the high Tc superconductivity in Bi2223. The answer can reveal the nature of the highest Tc in tri-layer cuprates and provide insights on how to raise Tc.