Complex Lattice and Charge Inhomogeneity Favoring Quantum Coherence in High-Temperature Superconductors

The presence of two components in the electron fluid of high-temperature superconductors and the complex charge and lattice inhomogeneity have been the hot topics of the international conference of the superstripes series, SUPERSTRIPES 2015, held in Ischia in 2015. The debate on the mechanisms for reaching room-temperature superconductors has been boosted by the discovery of superconductivity with the highest critical temperature in pressurized sulfur hydride. Different complex electronic and structural landscapes showing up in superconductors which resist to the decoherence effects of high temperature have been discussed. While low-temperature superconductors described by the BCS approximation are made of a single condensate in the weak coupling, the high-temperature superconductors are made of coexisting multiple condensates (in different spots of the k-space and the real space) some in the BCS-BEC crossover regime and others in the BCS regime. The role of “shape resonance” in the exchange interaction between these different condensates, like “the Fano-Feshbach resonance” in ultracold gasses, is emerging as a key term for high-temperature superconductivity.