In most conductors of electricity, the kinetic energy of electrons widely outweighs the Coulomb repulsion between electric charge carriers of similar sign. However, in the "Mott insulators", the Coulomb repulsion is at the same level as the kinetic energy of electrons. Yet, it is precisely this particularity that allows us to see quantum properties emerge, like high critical temperature superconductivity in some special crystalline structures such as cuprates.

However, can we quickly control the electronic properties of a material such as this without it heating up? It is of course possible to change the temperature or the chemical composition (by impurity doping) but it is a slow process. Yet recently, a superconducting transition, though short, was identified in cuprates illuminated by a femtosecond laser (10^-15s).

IPhT researchers Francesco Peronaci, Marco Schiro and Olivier Parcollet modeled this illumination in a Mott insulator. To this end, they adapted a traditional physics model of the condensed state, the Hubbard model, to a non-equilibrium state in the presence of a periodic disturbance over time (laser). When confronted to extremely high laser frequencies, electrons do not have the time to heat up. Thanks to their model, the physicists were able to show that a system of highly correlated electrons, such as a Mott insulator, does not heat up at all as long as the laser frequency stays under a finite value. However, as soon as the laser frequency reaches its resonant frequency, the system violently flares.

The theoreticians now hope to be able to explain the origin of the superconducting transition in the cuprates and to find out how to sustain it.