Drag effect and Cooper electron-hole pair fluctuations in a topological insulator film

Manifestations of fluctuating Cooper pairs formed by electrons and holes populating opposite surfaces of a topological insulator film in the Coulomb drag effect are considered. A fluctuational Aslamazov-Larkin contribution to the transresistance between surfaces of the film is calculated. The contribution is the most singular one in the vicinity of critical temperature T _d and diverges in the critical manner as ⁽ T ^- T _d ^)- 1. In the realistic conditions γ∼T _d , where γ is the average scattering rate of electrons and holes, the Aslamazov-Larkin contribution plays an important role and can dominate the fluctuation transport. The macroscopic theory based on the time-dependent Ginzburg-Landau equation is developed for a description of the transport in the system. The results can be easily generalized for other realizations of an electron-hole bilayer.