International audienceHeat can be exchanged between two surfaces through emission and absorption of thermal radiation. It has been predicted theoretically that for distances smaller than the peak wavelength of the blackbody spectrum, radiative heat transfer can be increased by the contribution of evanescent waves(1-8). This contribution can be viewed as energy tunnelling through the gap between the surfaces. Although these effects have already been observed(9-14), a detailed quantitative comparison between theory and experiments in the nanometre regime is still lacking. Here, we report an experimental setup that allows measurement of conductance for gaps varying between 30 nm and 2.5 mu m. Our measurements pave the way for the design of submicrometre nanoscale heaters that could be used for heat-assisted magnetic recording or heat-assisted lithography

Combining Scanning Gate Microscopy (SGM) experiments and simulations, we demonstrate low temperature imaging of electron probability density |Ψ| 2 (x, y) in embedded mesoscopic quantum rings (QRs). The tip-induced conductance modulations share the same temperature dependence as the Aharonov-Bohm effect, indicating that they originate from electron wavefunction interferences. Simulations of both |Ψ| 2 (x, y) and SGM conductance maps reproduce the main experimental observations and link fringes in SGM images to |Ψ| 2 (x, y). Thanks to the scanning tunnelling microscope (STM), remarkable precision has been achieved in the local scale imaging of surface electron systems. Only a few years after the STM invention, electron interferences could be visualized in real space inside artificially confined surface structures, the "quantum corrals" [1]. However, since they rely on the measurement of a current between a tip and the sample, STM techniques are useless when the system of interest is buried under an insulating layer, as in two-dimensional electron gases (2DEGs) confined in semiconductor heterostructures. To circumvent the obstacle, a new method was developed: the Scanning Gate Microscopy (SGM). SGM consists in mapping the conductance of the system as the polarized tip, acting as a flying nano-gate, scans at a constant distance above the 2DEG. SGM gave many valuable insights into the physics of quantum point contacts (QPCs) [7].[In some cases, the mechanism of SGM image formation is readily understandable. For example, in the vicinity of a QPC [2], coherent electron flow is imaged due to multiple reflections and interferences of electrons bouncing between the QPC and the tip-induced depleted region. In comparison, the situation seems more complex when the tip scans directly over an open mesoscopic billiard [6]: the tip perturbation extends over the whole system of interest, so that all semi-classical trajectories are modified. The mechanisms that link conductance maps to the properties of unperturbed electrons still need to be clarified. Recently, we showed that SGM images in the vicinity of a QR allow direct observation of iso-phase lines for electrons in an electrostatic Aharonov-Bohm (AB) experiment [8].In this Letter, we discuss SGM images obtained as the tip scans directly over coherent quantum rings (QRs). Experimentally, we find that the amplitude of conductance modulations shares a common temperature dependence with the Aharonov-Bohm effect, a direct evidence that SGM probes the quantum nature of electrons. On the other hand, we perform quantum mechanical simulations of SGM experiments. First, the amplitude of conductance fringes is found to evolve linearly at low perturbation amplitude, both in experiments and simulations. Second, we observe a direct correspondence between simulated SGM data and simulations of the electron probability density |Ψ| 2 (x, y, E F ). We deduce that, in this linear regime, SGM reliably maps |Ψ| 2 (x, y, E F ) in coherent QRs.We fabricated two QRs, samples R1 and R2, from an InGa...

It is shown that a graphene layer on top of a dielectric slab can dramatically influence the ability of this dielectric for radiative heat exchange. Effect of graphene is related to thermally excited plasmons. Frequency of these resonances lies in the terahertz region and can be tuned by varying the Fermi level through doping or gating. Heat transfer between two dielectrics covered with graphene can be larger than that between best known materials and even much larger at low temperatures. Moreover, high heat transfer can be significantly modulated by electrical means that opens up new possibilities for very fast manipulations with the heat flux.PACS numbers: 44.40.+a, 42.50.Lc, Radiative heat transfer (RHT) in vacuum at small distances between bodies is much increased in the near-field regime as compared to that given by the black body law [1][2][3]. It happens due to interaction of evanescent waves at distances small in comparison with the thermal wavelength λ T = c/T (here k B = 1). Particularly strong enhancement occurs when bodies can support surface modes such as plasmon-polaritons and phonon-polaritons [4,5]. This effect can be used to improve performance of near-field photovoltaic devices [6], in nanofabrication [7], and in near-field imaging systems [8].Graphene attracted recently enormous attention as a two dimensional carbon material with unusual electronic properties [9]. It is considered as a promising material for the development of high-performance electronic devices [10,11]. Plasmons in graphene show favorable behavior for applications such as large confinement, long propagating distances, and high tunability via electrostatic gating [12]. In contrast with nobel-metals the plasmon frequencies lie in the terahertz region that is interesting for radiative heat transfer, but the topic was not explored yet. Heat transfer was considered [13] only between closely spaced graphene and SiO 2 substrate where plasmons do not play significant role.Pristine graphene at zero temperature does not support plasmon excitations but doped material does [14]. On the other hand at finite temperature plasmons exist even for undoped material [15]. These thermoplasmons were shown to change significantly the thermal Casimir force for suspended graphene [16] and graphene-covered materials [17]. In this paper we show that plasmon excitations in graphene have striking effect on the near-field RHT between bodies if at least one of them is covered with graphene.Usual local materials have fixed frequencies of phononpolariton or plasmon-polariton resonances. Graphene is essentially nonlocal material and its plasmon frequency changes with the wavenumber. Moreover, it varies significantly with the doping level. These properties make plasmons in graphene a convenient tool to control the heat transfer between bodies.To evaluate the RHT between two bodies 1 and 2 one has to know the reflection coefficients r for each body as functions of the frequency ω and the wave vector q. These coefficients are different for each polarization µ = ...