Nonlocalizability of contact phenomena in composite, two-dimensional charged systems

A two-dimensional Corbino disk is used as an example to show that contact of an initially neutral, two-dimensional electronic system (2DEG) with ''external'' metal electrodes, whose internal characteristics are different from the 2DEG (the work functions are different), leads to breakdown of local neutrality of the two-dimensional part of the disk over the entire width of the disk. A classical description is given of anomalously long contact nonuniformities in the distribution of the 2D electron density. The role of quantum corrections to the classical theory is discussed. The effect of contact nonuniformities of the density on the linear part of the current-voltage characteristic of a Corbino sample under the conditions of the quantum Hall effect is discussed. The available experimental data for a Corbino disk, which indicate the existence of an equilibrium nonuniformity of the 2D electron density in the disk, are evaluated, In particular, the contact potential difference in this system is estimated. (C) 1995 American Institute of Physics.