impurity mediated interaction
A material's resistance originates from the diffusion of conduction electrons onto the material's defects (impurities, misarrangement etc.).
Mathematically these defects are described by a scattering potential. If the defects are charged, electrons want to hide (screen) this charge
and another potential builds up around the impurity. This self-consistent potential (the interaction potential) can also difuse electrons and therefore change the resistance of a material.
During my Phd in GHMFL, I studied the influence of this potential which varies strongly with temperature. I showed experimentally that there are in fact two regimes
of interaction depending on the temperature and impurity spacing. The transition between these regimes had never been observed.
To learn more, read the Physical Review B article or the free version downloadable at Cornell's archive.
boundary mediated interactions
Although poorly undestood, the interaction potential was well known when assisted by impurities. During my postdoc in the Quantum Solid State research group
at NTT BRL (Japan) we showed that this potential can also influence the conduction in systems without imputirties.
Indeed, this potential (see the image) also builds up at the boundaries of a system. If the boudaries are close enough, it can modify the conduction.
This result is important because electronic components shrink in dimensions and we may reach sizes where this effect my become dominant.
For more details, read the Physical Review Letters article or the free version downloadable at Cornell's archive.