Theory of Coulomb drag in spatially inhomogeneous 2D materials

Abstract

Coulomb drag between parallel two-dimensional electronic layers is an excellent tool for the study of electron-electron interactions. In actual experiments, the layers display spatial charge density fluctuations due to imperfections such as external charged impurities. However, at present a systematic way of taking these inhomogeneities into account in drag calculations has been lacking, making the interpretation of experimental data problematic. On the other hand, there exists a highly successful and widely accepted formalism describing transport within single inhomogeneous layers known as effective medium theory. In this work, we generalize the standard effective medium theory to the case of Coulomb drag between two inhomogeneous sheets and demonstrate that inhomogeneity in the layers has a strong impact on drag transport. In the case of exciton condensation between the layers, we show that drag resistivity takes on a value determined by the amplitude of density fluctuation. Next we consider drag between graphene sheets, in which the existence of spatial charge density fluctuations is well-known. We show that these inhomogeneities play a crucial role in explaining existing experimental data. In particular, the temperature dependence of the experimentally observed peaks in drag resistivity can only be explained by taking the layer density fluctuations into account. We also propose a method of extracting information on the correlations between the inhomogeneities of the layers. The effective medium theory of Coulomb drag derived here is general and applies to all two-dimensional materials.arXiv:1611.03089v2 [cond-mat.mes-hall]

First-principles quantum corrections for carrier correlations in double-layer two-dimensional heterostructures

“…5 to 7 to determine the nature of correlation between the layers. This would be especially useful for clarifying the source of the unexpected sign changes [85][86][87] in Coulomb drag experiments that have been explained by earlier works simply asserting correlation 61,88 or anti-correlation 60,62 without proof. In the case of bilayer graphene, Ref.…”

“…Of particular interest to us are situations that are not easily tackled with orbital-based techniques, for example 2D material sheets of mesoscopic size that are subjected to aperiodic disorder potentials. Such situations are for example of current interest in studies on Coulomb drag 59 where there exists an unsettled controversy as to whether the behavior of drag measured in experiment 60 is due to correlation 61 or anticorrelation 62 between the density fluctuations of the layers.…”

Effect of quasiparticle excitations and exchange-correlation in Coulomb drag in graphene

“…8c for both T ¼ 240 K and 300 K. In this case, the functional form of ρ D has been assessed separately for the k F d < 1 and k F d > 1 regimes, with ρ D varying as 1=d γ with γ ¼ 1:5 and 1.75, respectively. It should be noted that, close to the Dirac point, the effects of the charge density fluctuations, known as electronhole puddles, in the two graphene layers need to be taken into account 44 . In the calculations presented here, far from the Dirac point, these effects have been neglected.…”

Дефекты межслоевой поверхности и термоэлектрические свойства в слоистых пленках топологических изоляторов n-Bi-=SUB=-2-=/SUB=-Te-=SUB=-2.7-=/SUB=-Se-=SUB=-0.15-=/SUB=-S-=SUB=-0.15-=/SUB=-

“…Значительный интерес представляют теоретические [14,15] и экспериментальные [16,17] исследования эффекта сверхтекучести бозе-энштейновского конденсата межслоевых [15] экситонов, известных также как топологические [18] или двухслойные [9] экситоны, которые возникают благодаря сильному кулоновскому взаимодействию электронно-дырочных токов в пространственно разделенных проводящих слоях ТИ. В тонкопленочных двухслойных экситонных структурах на основе n-и p-типа Bi 2 Te 3 , разделенных изолирующим слоем, за счет кулоновского взаимодействия электроннодырочных пар на границе полупроводника и изолятора возникают межслоевые экситоны при оптимальных толщинах пленок и изолирующих слоев.…”