Exciton condensation and perfect Coulomb drag

摘要

Coulomb drag is a process whereby the repulsive interactions between electrons in spatially separated conductors enable a current flowing in one of the conductors to induce a voltage drop in the other. If the second conductor is part of a closed circuit, a net current will flow in that circuit. The drag current is typically much smaller than the drive current owing to the heavy screening of the Coulomb interaction. There are, however, rare situations in which strong electronic correlations exist between the two conductors. For example, double quantum well systems can support exciton condensates, which consist of electrons in one well tightly bound to holes in the other. 'Perfect' drag is therefore expected; a steady transport current of electrons driven through one quantum well should be accompanied by an equal current of holes in the other. Here we demonstrate this effect, taking care to ensure that the electron-hole pairs dominate the transport and that tunnelling of charge between the quantum wells, which can readily compromise drag measurements, is negligible. We note that, from an electrical engineering perspective, perfect Coulomb drag is analogous to an electrical transformer that functions at zero frequency.%从一个导体中流过的电流，能够通过被称为rn“库仑相互作用”的电子—电子排斥力在另一rn个与第一个在空间上分开的导体中诱导产生电rn流。这样所产生的“拖拽电流”通常较小，但rn人们一直认为，在某些情况下这一电流有可能rn与驱动电流具有相同的量级。现在，这一预测rn通过在一个双层二维电子系统中对“完美”拖rn拽的演示得到了证实。在该系统中，一层电子rn被耦合到有相同数量空穴的另一层电子上，它rn们一起能够形成一个激子凝聚态。本文作者们rn明确认为，第一层中的电子流能在第二层中驱rn动产生一个相等的、但相反的电子流。