Tunnel and thermal c-axis transport in BSCCO in the normal and pseudogap states

We consider the problem of c -axis transport in double-layered cuprates, in particular with reference to Bi 2 Sr 2 CaCu 2 O 8+? compounds. We exploit the effect of the two barriers on the thermal and tunnel transport. The resulting model is able to describe accurately the normal state c -axis resistivity in Bi 2 Sr 2 CaCu 2 O 8+? , from the underdoped side up to the strongly overdoped. We extend the model, without introducing additional parameters, in order to allow for the decrease of the barrier when an external voltage bias is applied. The extended model is found to describe properly the c -axis resistivity for small voltage bias above the pseudogap temperature T * , the c -axis resistivity for large voltage bias even below T c , and the differential d I /d V curves taken in mesa structures.