Role of contacts in mesoscopic devices

The conductance of a mesoscopic device is usually described in terms of the transmission of electrons between electrical contacts. Implicit in this description is the assumption that contacts can be approximated as ideal thermal reservoirs which act solely to thermalise incident electrons before re-injecting them into the device. We describe two classes of experiment where this assumption is not valid. First, when the dissipation in the system is strongly dependent on an external parameter, such as temperature or magnetic field, the physical position of the contact may itself depend the parameter. We study this by investigating the transport properties of quantum wires with disordered contacts. Second, when there is the possibility of some sort of interaction between the electrons in the contact and those in the device, as we find in resonant tunnelling from a 2D contact into a 0D state. In both cases we find that the conductance properties of the device are strongly modified by the nature of the contact.