Transport Properties of Holographic Defects
  We study the charge transport properties of fields confined to a (2+1)-dimensional defect coupled to (3+1)-dimensional super-Yang-Mills at large-$\nc$ and strong coupling, using AdS/CFT techniques applied to linear response theory. The dual system is described by $\nf$ probe D5- or D7-branes in the gravitational background of $\nc$ black D3-branes. Surprisingly, the transport properties of both defect CFT's are essentially identical -- even though the D7-brane construction breaks all supersymmetries. We find that the system possesses a conduction threshold given by the wave-number of the perturbation and that the charge transport arises from a quasiparticle spectrum which is consistent with an intuitive picture where the defect acquires a finite width. We also examine finite-$\lambda$ modifications arising from higher derivative interactions in the probe brane action. 
Robert C. Myers and Matthias C. Wapler