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Register a new userHeat Transport Through Plasmonic Interactions in Closely Spaced Metallic Nanoparticles Chains
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Philippe Ben-Abdallah
Publication date
2008
fields
Physics
and research's language is
English
Authors
Philippe Ben-Abdallah
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We report a numerical investigation on the heat transfer through one dimensional arrays of metallic nanoparticles closely spaced in a host material. Our simulations show that the multipolar interactions play a crucial role in the heat transport via collective plasmons. Calculations of the plasmonic thermal conductance and of the thermal conductivity in ballistic and diffusive regime, respectively have been carried out. (a) Using the Landauer-Buttiker formalism we have found that, when the host material dielectric constant takes positive values, the multipolar interactions drastically enhance by several order of magnitude the ballistic thermal conductance of collective plasmons compared with that of a classical dipolar chain. On the contrary, when the host material dielectric constant takes negative values, we have demonstrated the existence of non-ballistic multipolar modes which annihilate the heat transfer through the chains. (b) Using the kinetic theory we have also examined the thermal behavior of chains in the diffusion approximation. We have shown that the plasmonic thermal conductivity of metallic nanoparticle chains can reach 1% of the bulk metal thermal conductivity . This result could explain the anomalously high thermal conductivity observed in many colloidal suspensions, the so called nanofluids.
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Anisotropic plasmon coupling in closely-spaced chains of Ag nanoparticles was visualized using the electron energy loss spectroscopy in a scanning transmission electron microscope. For dimers as the simplest chain, mapping the plasmon excitations with nanometers spatial resolution and 0.27 eV energy resolution intuitively identified two coupling plasmons. The in-phase mode redshifted from the ultraviolet region as the inter-particle spacing was reduced, reaching the visible range at 2.7 eV. Calculations based on the discrete dipole approximation confirmed its optical activeness, where the longitudinal direction was constructed as the path for light transportation. Two coupling paths were then observed in an inflexed 4-particle chain.
Metallic atomic junctions pose the ultimate limit to the scaling of electrical contacts. They serve as model systems to probe electrical and thermal transport down to the atomic level as well as quantum effects occurring in one-dimensional systems. Charge transport in atomic junctions has been studied intensively in the last two decades. However, heat transport remains poorly characterized because of significant experimental challenges. Specifically the combination of high sensitivity to small heat fluxes and the formation of stable atomic contacts has been a major hurdle for the development of this field. Here we report on the realization of heat transfer measurements through atomic junctions and analyze the thermal conductance of single atomic gold contacts at room temperature. Simultaneous measurements of charge and heat transport reveal the proportionality of electrical and thermal conductance, quantized with the respective conductance quanta. This constitutes an atomic scale verification of the well-known Wiedemann-Franz law. We anticipate that our findings will be a major advance in enabling the investigation of heat transport properties in molecular junctions, with meaningful implications towards the manipulation of heat at the nanoscale
We describe a technique to fabricate closely spaced electron-hole bilayers in GaAs-AlGaAs heterostructures. Our technique incorporates a novel method for making shallow contacts to a low density ($<10^{11}cm^{-2}$) 2-dimensional electron gas (2DEG) that do not require annealing. Four terminal measurements on both layers (25nm apart) are possible. Measurements show a hole mobility $mu_{h}>10^{5}{rm cm}^{2}{rm V}^{-1}{rm s}^{-1}$ and an electron mobility $mu_{e}>10^{6}{rm cm}^{2}{rm V}^{-1}{rm s}^{-1}$ at 1.5K. Preliminary drag measurements made down to T=300mK indicate an enhancement of coulomb interaction over the values obtained from a static Random Phase Approximation (RPA) calculation.
The transport properties of junctions composed of a central region tunnel-coupled to external electrodes are frequently studied within the single-impurity Anderson model with Hubbard on-site interaction. In the present work, we supplement the model with an important ingredient, namely the charge-bond interaction, also known as correlated or assisted hopping. Correlated hopping enters the second-quantised Hamiltonian, written in the Wannier representation, as an off-diagonal many-body term. Using the equation of motion technique, we study the effect of the correlated hopping on the spectral and transport characteristics of a two-terminal quantum dot. Two different Green functions (GFs) appear: one of them describes the spectral properties of the quantum dot, the other the transport properties of the system. The calculation of the transport GF requires the knowledge of the spectral one. We use decoupling procedures similar to those which properly describe the standard Anderson model within the Kondo regime and outside of it. For an arbitrary ratio $x$ between the amplitudes of correlated and single-particle hopping terms, the transport GF fulfils the $x leftrightarrow 2-x$ symmetry of the model. The average occupation of the dot also obeys this symmetry, albeit the spectral function of the quantum dot, calculated within an analogous decoupling scheme as for the transport GF, does not. We identify the physical reason for this behavior, and propose a way to cure it. Since the correlated-hopping term breaks the particle-hole symmetry of the model and modifies all transport characteristics of the system, the detailed knowledge of its influence on measurable characteristics is a prerequisite for its experimental detection. Simple, experimentally feasible methods are proposed.
There is so far no clear-cut experimental analysis that can determine whether dipole-dipole interactions enhance or reduce the blocking temperature $T_{B}$ of nanoparticle assemblies. It seems that the samples play a central role in the problem and therefore, their geometry should most likely be the key factor in this issue. Yet, in a previous work, Jonsson and Garcia-Palacios did investigate theoretically this problem in a weak-interaction limit and without the presence of an external DC field. Based on symmetry arguments they reached the conclusion that the variation of the relaxation rate is monotonous. In the presence of an external magnetic field we show that these arguments may no longer hold depending on the experimental geometry. Therefore, the aim of this paper is to evaluate the variation of $T_{B}$ for a model system consisting of a chain of ferromagnetic nanoparticles coupled with long-range dipolar interaction with two different geometries. Rather than addressing a quantitative analysis, we focus on the qualitative variation of $T_{B}$ as a function of the interparticle distance a and of the external field $h$. The two following situations are investigated: a linear chain with a longitudinal axial anisotropy in a longitudinal DC field and a linear chain with a longitudinal axial anisotropy in a transverse field.
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