We report a fully microscopic theory for transconductivity, or, equivalently, momentum transfer rate, of Coulomb coupled electron systems. We use the Kubo linear response formalism, and our main formal result expresses the transconductivity in terms of two fluctuation diagrams, which are topologically related, but not equivalent to, the Aslamazov-Larkin diagrams known for superconductivity. Previously reported results are shown to be special cases of our general expression; specifically, for constant impurity scattering rates, we recover the Boltzmann equation results in the semiclassical clean limit, and the memory function results in dirty systems. Furthermore, we show that for energy dependent relaxation times, the final result is not expressible in terms of standard density-response functions. Other new results include: (i) at T = 0, the frequency dependence of the transfer rate is found to be proportional to Ω and Ω 2 for frequencies below and above the impurity

We derive an expression for the drag rate (i.e., interlayer momentum transfer rate) for carriers in two coupled two-dimensional gases to lowest nonvanishing order in the screened interlayer electron-electron interaction, valid for arbitrary intralayer scattering mechanisms, using the Boltzmann transport equation. We calculate the drag rate for experimentally relevant parameters, and show that for moderately high temperatures (T > ∼ 0.2T F , where T F is the Fermi temperature) the dynamical screening of the interlayer results in a large enhancement of the drag rate due to the presence of coupled plasmon modes. This plasmon enhancement causes the scaled drag rate to have a peak (i) as a function of temperature at T ≈ 0.5T F , and (ii) as a function of the ratio of densities of the carriers in the two layers when their Fermi velocities are equal. We also show that the drag rate can be significantly affected by the intralayer scattering mechanisms; in particular, the drag rate changes approximately by a factor of 2 when the dopant layer modulation doped structures are moved in from 400Å to 100Å. 73.50.Dn, 73.20.Mf

We show theoretically that the Coulomb drag rate between two parallel quasi-two-dimensional electron gases is substantially enhanced by the coupled acoustic and optic plasmon modes of the system at temperatures T > ∼ 0.2T F (where T F is the Fermi temperature) for experimentally relevant parameters.The acoustic mode causes a sharp upturn in the scaled drag rate as a function of temperature at T ≈ 0.2T F . Other experimental signatures of plasmondominated drag are a d −3 dependence on the well separation d, and a peak in the drag rate as a function of relative carrier densities at matched Fermi velocities.73.50.Dn, 73.20.Mf Typeset using REVT E X

We consider hot carrier inelastic scattering due to electron-electron interactions in graphene, as functions of carrier energy and density. We calculate the imaginary part of the zero-temperature quasiparticle self-energy for doped graphene, utlizing the G0W and random phases approximations. Using the full dynamically screened Coulomb interaction, we obtain the inelastic quasiparticle lifetimes and associated mean free paths. The linear dispersion of graphene gives lifetime energy dependences that are qualitatively different from those of parabolic-band semiconductors. We also get good agreement with data from angle-resolved photoemission spectroscopy experiments.

We study the Coulomb drag between two single graphene sheets in intrinsic and extrinsic graphene systems with no interlayer tunneling. The general expression for the nonlinear susceptibility appropriate for single-layer graphene systems is derived using the diagrammatic perturbation theory, and the corresponding exact zerotemperature expression is obtained analytically. We find that, despite the existence of a nonzero conductivity in an intrinsic graphene layer, the Coulomb drag between intrinsic graphene layers vanishes at all temperatures. In extrinsic systems, we obtain numerical results and an approximate analytical result for the drag resistivity D , and find that D goes as T 2 at low temperature T, as 1/d 4 for large layer separation d, and 1 / n 3 for high carrier density n. We also discuss qualitatively the effect of plasmon-induced enhancement on the Coulomb drag, which should occur at a temperature of the order of or higher than the Fermi temperature.Introduction. With the recent advent of the experimental fabrication of a single layer of graphene, the electronic and transport properties of this newly discovered material have been intensively studied both experimentally 1,2 and theoretically. 2-4 Whereas electronic structure experiments have revealed detailed subtle many-body effects on the graphene energy spectrum, transport experiments on graphene have also revealed some unusual features, most noticeably, the nonzero minimum conductivity around zero bias gate voltage. 1 Up to now, the transport experiments performed have been focused only on the longitudinal and Hall transport properties 1,5 ͑in both weak and strong magnetic fields, including the quantum Hall regime͒ and weak localization. 6 All these phenomena depend on the physics of scattering of individual single quasiparticle from impurities, with electron-electron many-body interaction effects playing a quantitatively minor role. In two-dimensional electron gas ͑2DEG͒ semiconductor double-layer structures ͑e.g., modulation-doped GaAs/ Al x Ga 1−x As double quantum wells͒, electron-electron scattering between the 2DEG layers gives rise to the Coulomb drag effect, where a "drag" current is induced purely from the momentum exchanges through interlayer electron-electron scattering events. 7-9 One measures the effect of Coulomb drag by the drag resistivity defined by D = E pas. / J act. , where E pas. is the drag electric field in the open-circuited passive layer and J act. is the current density in the active layer. In high-mobility samples where the disorder is weak, D goes as T 2 at low temperatures T, and as d −4 for large double-layer separation d ͑see Refs. 7 and 10͒.In this paper, we investigate the Coulomb drag in graphene double-layer systems, considering both the intrinsic ͓chemical potential = Dirac pt. ͑=0 in this paper͔͒ and extrinsic ͑ 0͒ cases. So that there is no semantic confusion in what we mean by double-layer graphene, we emphasize that in our terminology "double-layer" means two isolated parallel two-dimensional ͑2D͒ monolayers s...

We consider theoretically the electron-electron interaction induced exchangecorrelation effects in the lowest subband of a quasi-one-dimensional GaAs quantum wire structures. We calculate, within the leading order dynamical screening approximation (i.e. the so-called GW approximation of the electron gas theory), the electron self-energy, spectral function, momentum distribution function, inelastic scattering rate, band gap renormalization, and, the many-body renormalization factor both at zero and finite temperatures, and, both with and without impurity scattering effects.We also calculate the effects of finite temperatures and finite impurity scattering on the many-body properties. We propose the possibility of a hot-electron transistor device with a large negative differential resistance which is based on the sudden onset of plasmon emission by energetic ballistic electrons in one dimension. The issue of the existence or non-existence of the Fermi surface among the interacting onedimensional quantum wire electrons is critically discussed based on our numerical results.

At temperatures comparable to the Fermi temperature, we have measured a plasmon enhanced Coulomb drag in a GaAs/AlGaAs double quantum well electron system. This measurement provides a probe of the many-body corrections to the coupled plasmon modes, and we present a detailed comparison between experiment and theory testing the validity of local field theories. Using a perpendicular magnetic field to raise the magnetoplasmon energy we can induce a crossover to single-particle Coulomb scattering.

Nanogel-based nanoplatforms have become a tremendously promising system of drug delivery. Nanogels constructed by chemical crosslinking or physical self-assembly exhibit the ability to encapsulate hydrophilic or hydrophobic therapeutics, including but not limited to small-molecule compounds and proteins, DNA/RNA sequences, and even ultrasmall nanoparticles, within their 3D polymer network. The nanosized nature of the carriers endows them with a specific surface area and inner space, increasing the stability of loaded drugs and prolonging their circulation time. Reactions or the cleavage of chemical bonds in the structure of drug-loaded nanogels have been shown to trigger the controlled or sustained drug release. Through the design of specific chemical structures and different methods of production, nanogels can realize diverse responsiveness (temperature-sensitive, pH-sensitive and redox-sensitive), and enable the stimuli-responsive release of drugs in the microenvironments of various diseases. To improve therapeutic outcomes and increase the precision of therapy, nanogels can be modified by specific ligands to achieve active targeting and enhance the drug accumulation in disease sites. Moreover, the biomembrane-camouflaged nanogels exhibit additional intelligent targeted delivery features. Consequently, the targeted delivery of therapeutic agents, as well as the combinational therapy strategy, result in the improved efficacy of disease treatments, though the introduction of a multifunctional nanogel-based drug delivery system.