# Boltzmann-Langevin theory: Applications to Coulomb drag

Monday, March 26, 2018 - 4:00pm - 5:00pm

Lind 409

Alex Levchenko (University of Wisconsin, Madison)

We will review the Boltzmann-Langevin transport theory in general and its description of the Coulomb drag effect in clean double-layer systems in particular. Coulomb drag arises from density fluctuations with spatial scales of order of interlayer separation. At low temperatures, their characteristic frequencies exceed the intralayer equilibration rate of the electron liquid, and Coulomb drag may be treated in the collisionless approximation. As temperature is raised, the electron mean free path becomes short due to electron-electron scattering. This leads to local equilibration of electron liquid, and consequently drag is determined by hydrodynamic density modes. Boltzmann-Langevin theory applies to both the collisionless and the hydrodynamic regimes, and it enables one to describe the crossover between them. We will find that drag resistivity exhibits a nonmonotonic temperature dependence with multiple crossovers at distinct energy scales. At the lowest temperatures, Coulomb drag is dominated by the particle-hole continuum, whereas at higher temperatures of the collision-dominated regime it is governed by the plasmon modes.