Ricerc@Sapienza

Equilibrium states at ¿negative¿ absolute temperature are found when the entropy of a system is a decreasing function of its total energy, i.e. when providing additional energy results in a contraction of the phase-space volume accessible to the system. Negative absolute temperatures are well known to characterize, for instance, the high-energy limit of nuclear spins systems, cold atoms trapped in optical lattices and interacting vortexes in two-dimensional hydrodynamics.

In recent years studies on negative-temperature equilibrium states were also carried out by mean of simple one-dimensional chains of Hamiltonian oscillators with bounded and periodic kinetic terms. The aim of this project is to study the behavior of those chains when they are driven out of equilibrium by two thermal baths imposing different temperatures at the boundaries (even with opposite signs). A systematic investigation of those models will allow for a better understanding of dynamical properties of systems with negative temperature in out-of-equilibrium conditions.

An extensive employment of GPU computer simulations will be able to characterize the properties of out-of-equilibrium response functions in those models, in presence of negative absolute temperature conditions. This will be an important step to understand the relation between response, temperature and transport properties. A particularly intriguing situation is obtained by imposing temperatures with opposite signs to the boundaries of the chain, resulting in a spatial cross-over between positive and negative temperature; in this case it is not clear what would be the effect on the T>0 region of a local perturbation in the T