Emergent phenomena from correlation and competition: a case of figure from high temperature superconductivity
Marcello Civelli (LPS Orsay)
Emergent phenomena are common in correlated systems. For instance, in correlated quantum materials novel phases appear displaying remarkable properties, like e.g. colossal magneto-resistance, exotic charge and magnetic order, quantum criticality, unconventional superconductivity….Tuning the system from one phase to another via the application of an external parameter, like temperature, pressure, doping, or by manipulating intrinsic parameters via, for example, light-matter interaction, offer the possibility to exploit a large variety of different functionalities on the same device and opens the route to the development of novel technologies.
Two main concepts that frame the emergence of novel phenomena from correlation have been at the front stage. On one side the competition between quantum phases, famously advocated for example in the case of quantum critical phase transitions in heavy fermion compounds. On the other side, the idea that “more is different” (P.W. Anderson), i.e. that our understanding of these new quantum phenomena require a new quantum state of matter, sharply different from the ones that we have known so far.
We shall show how these two concepts merge in the most known exotic state of matter rising from correlation, the high-temperature superconductivity in cuprates. The scenario that we propose is obtained by resolving the Hubbard Model, which is the simplest model capturing the salient features of cuprates. In particular we shall show that an unprecedented form of superconducting pairing arises from correlation, requiring to go beyond the main concepts of unconventional superconductivity developed so far.