Integrable transport anomalies and the emergence of boundary resistances

Transport phenomena are central to physics: A typical situation is when two macroscopically different classical or quantum piece of matter are joint together and the whole system experiences an energy or particle stream flowing from one side to the other. Transport phenomena are fundamental to engineer Non-Equilibrium Stationary-States (NESS) indeed, and in the fully-quantum and many-body realms they are attracting an increasing amount of attention. Quantum(NESS) strongly affects the transport properties in low dimension and, recently, a new generalised hydrodynamic (GHD) picture has been developed for interacting integrable models: It has been shown that such models do support ballistic transport of excitations at all energies. But what does it happen when two different integrable models are joint together?
This question has been addressed by Mario Collura and collaborators by studying the energy and magnetisation currents in non homogenous spin chains. The two pieces of "integrable materials" support different energy carriers in the bulk, however the full system is not integrable anymore: Nearby the junction a sub-ballistic region emerges, with a strong tendency towards thermalisation.  
Suppression of energy and particle flow is accompanied by a local entanglement entropy growth as well; moreover, at infinite time the system displays a discontinuity in the local effective temperature at the junction, thus indicating the presence of a non-vanishing Kapitza boundary resistance: This is the only parameter which enters into the theoretical description of the phenomenon and it establishes a bridge between ballistic and diffusive behaviours. As a matter of fact, this study paves definitively the way to the analysis of the interplay between transport, integrability, and local defects. 
 
Full paper here
 

Dated: November 8, 2019