Palestrante: Thaís Victa Trevisan (UEC/IFGW/DFMC)

Resumo: The nature of the superconducting (SC) state of doped SrTiO₃ remains a subject of intense research. It is known experimentally that its SC transition temperature T_c displays a double a dome shape as function of the carrier density n. Quantum oscillations experiments reveal, in agreement with first principle calculation and earlier quantum tunneling experiments, that multiple bands become occupied as the concentration n changes, i.e., STO is a multi-band superconductor. In the low density region of the phase diagram, at critical concentration where the second band starts to be populated, the topology of the Fermi surface changes and the system undergoes a Lifshitz transition (LT). Surprisingly, around this critical concentration, it is observed a suppression of T_c . The same phenomenon happens in the interface LAO/STO. The origin of such a suppression of T_c across a LT remains widely debated and we show that it can be explained due to the combination of disorder and repulsive inter-band interactions, since in this case the pair-breaking effect caused by inter-band impurity scattering can overcome the increase of T_c favored by the enhancement of the density of states. We also show that this process is accompanied by a change of symmetry of the SC state from s^+- to s⁺⁺, indicating that STO is an unconventional multi-band superconductor