Study of radiative heat transfer in Ångström- and nanometre-sized gaps

Cui, Longji; Jeong, Wonho; Fernández-Hurtado, Víctor; Feist, Johannes; García‐Vidal, F. J.; Cuevas, Juan Carlos; Meyhöfer, Edgar; Reddy, Pramod

doi:10.1038/ncomms14479

Cited by 153 publications

(173 citation statements)

References 56 publications

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“…But it is also interesting to examine the tunneling regime, when contacts are broken. This regime is still challenging for experimentalists, since signals are rather small and contamination of surfaces may play a crucial role [79]. Moreover, as the gap between the electrodes increases, at some point the thermal radiation via photon tunneling may give a contribution of similar order [54].…”

Section: Dft-based Transport Results: Phonon Transportmentioning

confidence: 99%

Thermal conductance of metallic atomic-size contacts: Phonon transport and Wiedemann-Franz law

et al. 2017

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], we present here an extensive theoretical analysis of the thermal conductance of atomic-size contacts made of three different metals, namely gold (Au), platinum (Pt), and aluminum (Al). The main goal of this work is to elucidate the role of phonons in the thermal transport through these atomic contacts as well as to study the validity of the Wiedemann-Franz law, which relates the electrical and the thermal conductance. For this purpose, we have employed two different custom-developed theoretical approaches. The first one is a transport method based on density functional theory (DFT) that allows one to accurately compute the contributions of both electrons and phonons to the thermal transport in few-atom-thick contacts. The second technique is based on a combination of classical molecular dynamics (MD) simulations and a tight-binding model that enables the efficient calculation of the electronic contribution to the thermal conductance of atomic contacts of larger size. Our DFT-based calculations show that the thermal conductance of few-atom contacts of Au and Pt is dominated by electrons, with phonons giving a contribution typically below 10% of the total thermal conductance, depending on the contact geometry. For these two metals we find that the small deviations from the Wiedemann-Franz law, reported experimentally, largely stem from phonons. In the case of Al contacts we predict that the phononic contribution can be considerably larger with up to 40% of the total thermal conductance. We show that these differences in the phononic contribution across metals originate mainly from their distinct Debye energies. On the other hand, our MD-based calculations demonstrate that the electronic contribution to the thermal conductance follows very closely the Wiedemann-Franz law, irrespective of the material and the contact size. Finally, the ensemble of our results consistently shows that the reported observation of quantized thermal transport at room temperature is restricted to few-atom contacts of Au, a monovalent metal in which the transport is dominated by the s valence orbitals. In the case of multivalent metals like Pt and Al this quantization is statistically absent due to the fact that additional orbitals contribute to the transport with conduction channels that have intermediate transmissions between 0 and 1, even in the case of single-atom contacts.

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Section: Dft-based Transport Results: Phonon Transportmentioning

confidence: 99%

Thermal conductance of metallic atomic-size contacts: Phonon transport and Wiedemann-Franz law

et al. 2017

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“…Recent advancement in the experimental instruments and operational protocols has enabled the measurement of heat flow through nano-devices with a resolution of picowatts [297][298][299][300][301][302]. Presently, the calorimeters have been applied to monitor cellular activities [303,304]; and to study radiative heat transfer [305][306][307][308][309][310], thermal conductivity of nanostructures [311][312][313][314][315], and phase transitions of nanomaterials [316].…”

Section: General Principle Of Nanocalorimetric Techniquesmentioning

confidence: 99%

Local temperatures out of equilibrium

2019

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The temperature of a physical system is operationally defined in physics as "that quantity which is measured by a thermometer" weakly coupled to, and at equilibrium with the system. This definition is unique only at global equilibrium in view of the zeroth law of thermodynamics: when the system and the thermometer have reached equilibrium, the "thermometer degrees of freedom" can be traced out and the temperature read by the thermometer can be uniquely assigned to the system. Unfortunately, such a procedure cannot be straightforwardly extended to a system out of equilibrium, where local excitations may be spatially inhomogeneous and the zeroth law of thermodynamics does not hold. With the advent of several experimental techniques that attempt to extract a single parameter characterizing the degree of local excitations of a (mesoscopic or nanoscale) system out of equilibrium, this issue is making a strong comeback to the forefront of research. In this paper, we will review the difficulties to define a unique temperature out of equilibrium, the majority of definitions that have been proposed so far, and discuss both their advantages and limitations. We will then examine a variety of experimental techniques developed for measuring the non-equilibrium local temperatures under various conditions. Finally we will discuss the physical implications of the notion of local temperature, and present the practical applications of such a concept in a variety of nanosystems out of equilibrium. Figure 4: (a) The product of the density of states η(E) times the global distribution function ϕ|ρ|ϕ forms a strongly pronounced peak at the expectation value of the global system energyĒ. (b) The logarithm of the local distribution function a|ρ|a (solid line) and the logarithm of a canonical distribution (dashed line) with the same local temperature for a harmonic chain. (a) and (b) are reprinted with permission from [74].

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“…In nanojunctions heat transport via photons may yield another contribution, beside those of electrons and phonons discussed here. Indeed evanescent waves can enhance radiative thermal transport contributions in nanogaps, as studied in recent experiments [29][30][31]. Since we focus in this work on the contact regime and the precise magnitude depends on assumptions about the macroscopic shape of the electrodes [32], we will neglect radiative heat transport.…”

Section: Introductionmentioning

confidence: 99%

Statistical analysis of electronic and phononic transport simulations of metallic atomic contacts

et al. 2019

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We adapt existing phonon heat transport methods to compute the phononic thermal conductance of metallic atomic contacts during a stretching process. Nonequilibrium molecular dynamics (NEMD) simulations are used to generate atomic configurations and to simultaneously determine the phononic thermal conductance. Combining the approach with established electronic structure calculations based on a tight-binding parameterization allows us to calculate in addition charge transport properties of each contact geometry within the Landauer-Büttiker formalism. The method is computationally fast enough to perform a statistical analysis of many stretching events, and we apply it here to atomic junctions formed from three different metals, namely gold (Au), platinum (Pt) and aluminum (Al). The description of both phononic and electronic contributions to heat transport allows us to examine the validity of the Wiedemann-Franz law at the atomic scale. We find that it is well obeyed in the contact regime at room temperature for Au and Al as far as only electronic contributions are concerned, but deviations of up to 10% arise for Pt. If the total thermal conductance is studied, deviations of typically less than 10% arise for Au and Al, which can be traced back mainly to phononic contributions to the thermal conductance, while electronic and phononic contributions can add up to some 20% for single-atom contacts of Pt. arXiv:1907.08403v1 [cond-mat.mes-hall]

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Study of radiative heat transfer in Ångström- and nanometre-sized gaps

Cited by 153 publications

References 56 publications

Thermal conductance of metallic atomic-size contacts: Phonon transport and Wiedemann-Franz law

Thermal conductance of metallic atomic-size contacts: Phonon transport and Wiedemann-Franz law

Local temperatures out of equilibrium

Statistical analysis of electronic and phononic transport simulations of metallic atomic contacts

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