Using a block of three separated solid elements, a thermal source and drain together with a gate made of an insulator-metal transition material exchanging near-field thermal radiation, we introduce a nanoscale analog of a field-effect transistor that is able to control the flow of heat exchanged by evanescent thermal photons between two bodies. By changing the gate temperature around its critical value, the heat flux exchanged between the hot body (source) and the cold body (drain) can be reversibly switched, amplified, and modulated by a tiny action on the gate. Such a device could find important applications in the domain of nanoscale thermal management and it opens up new perspectives concerning the development of contactless thermal circuits intended for information processing using the photon current rather than the electric current.

We present measurements of the near-field heat transfer between the tip of a thermal profiler and planar material surfaces under ultrahigh vacuum conditions. For tip-sample distances below 10 −8 m our results differ markedly from the prediction of fluctuating electrodynamics. We argue that these differences are due to the existence of a material-dependent small length scale below which the macroscopic description of the dielectric properties fails, and discuss a corresponding model which yields fair agreement with the available data. These results are of importance for the quantitative interpretation of signals obtained by scanning thermal microscopes capable of detecting local temperature variations on surfaces.PACS numbers: 44.40.+a, 03.50.De, 78.20.Ci Radiative heat transfer between macroscopic bodies increases strongly when their spacing is made smaller than the dominant wavelength λ th of thermal radiation. This effect, caused by evanescent electromagnetic fields existing close to the surface of the bodies, has been studied theoretically already in 1971 by Polder and van Hove for the model of two infinitely extended, planar surfaces separated by a vacuum gap [1], and re-investigated later by Loomis and Maris [2] and Volokitin and Persson [3,4]. While early pioneering measurements with flat chromium bodies had to remain restricted to gap widths above 1 µm [5], and later studies employing an indium needle in close proximity to a planar thermocouple remained inconclusive [6], an unambiguous demonstration of near-field heat transfer under ultrahigh vacuum conditions and, thus, in the absence of disturbing moisture films covering the surfaces, could be given in Ref. [7].The theoretical treatment of radiative near-field heat transfer is based on fluctuating electrodynamics [8]. Within this framework, the macroscopic Maxwell equations are augmented by fluctuating currents inside each body, constituting stochastic sources of the electric and magnetic fields E and H. The individual frequency components j(r, ω) of these currents are considered as Gaussian stochastic variables. According to the fluctuationdissipation theorem, their correlation function reads [9]where E(ω, β) = ω/ exp(β ω) − 1 , with the usual inverse temperature variable β = 1/(k B T ); the angular brackets indicate an ensemble average. Moreover, ǫ ′′ (ω) denotes the imaginary part of the complex dielectric function ǫ(ω) = ǫ ′ (ω) + iǫ ′′ (ω). It describes the dissipative properties of the material under consideration, which is assumed to be homogeneous and non-magnetic. Thus, Eq. (1) contains the idealization that stochastic sources residing at different points r, r ′ are uncorrelated, no matter how small their distance may be. Applied to a material occupying the half-space z < 0, facing the vacuum in the complementary half-space z > 0, these propositions can be evaluated to yield the electromagnetic energy density in the distance z above the surface, giving [10]dκ ρ E (ω, κ, β, z) + ρ H (ω, κ, β, z)

We study the near-field heat exchange between hyperbolic materials and demonstrate that these media are able to support broadband frustrated modes which transport heat by photon tunnelling with a high efficiency close to the theoretical limit. We predict that hyperbolic materials can be designed to be perfect thermal emitters at nanoscale and derive the near-field analog of the blackbody limit.PACS numbers: 44.40.+a;81.05.Xj A black body is usually defined by its property of having a maximum absorptivity and therefore also a maximum emissivity by virtue of Kirchhoff's law [1]. The energy transmission between two black bodies having different temperatures obey the well-known Stefan-Boltzmann law. This law sets an upper limit for the power which can be transmitted by real materials, but it is itself a limit for the far-field only, since it takes only propagating modes into account. In terms of the energy transmission between two bodies the black body case corresponds to maximum transmission for all allowed frequencies ω and all wave vectors smaller than ω/c, where c is the vacuum light velocity. This means that all the propagating modes are perfectly transmitted across the separation gap.In the near-field regime, i.e., for distances smaller than the thermal wavelength λ th = c/k B T (2π is Planck's constant, k B is Boltzmann's constant, and T is the temperature) the radiative heat flux is not due to the propagating modes, but it is dominated by evanescent waves [2-4] and especially surface polaritons as confirmed by recent experiments [5][6][7][8][9][10][11]. The common paradigm is that the largest heat flux can be achieved when the materials support surface polaritons which will give a resonant energy transfer restricted to a small frequency band around the surface mode resonance frequency [3,4,12,13]. Many researchers have tried to find materials enhancing the nanoscale heat flux due to the contribution of the coupled surface modes by using layered materials [14,15] In the present work the aim is twofold: (i) We show, that materials supporting a broad band of evanescent frustrated modes can outperform the heat flux due to surface modes. This provides new possibilies for designing materials giving large nanoscale heat fluxes which could be used for thermal management at the nanoscale for instance. (ii) We derive a general limit for the heat flux carried by the frustrated modes and show that it is, in fact, the near-field analog of the usual black body limit. For the evanescent modes a near field analog of a black body can be defined in the sense that the energy transmission coefficient must be equal to one for all frequencies and all wave vectors larger than ω/c. With today's nanofabrication techniques it is possible to manufacture artificial materials such as photonic band gap materials and metamaterials which exhibit very unusual material properties like negative refraction [23]. Due to such properties they are considered as good candidates for perfect lensing [24,25], for repulsive Casimir forces [26][27][28][...

In this Letter a N -body theory for the radiative heat exchange in thermally non equilibrated discrete systems of finite size objects is presented. We report strong exaltation effects of heat flux which can be explained only by taking into account the presence of many body interactions. Our theory extends the standard Polder and van Hove stochastic formalism used to evaluate heat exchanges between two objects isolated from their environment to a collection of objects in mutual interaction. It gives a natural theoretical framework to investigate the photon heat transport properties of complex systems at mesoscopic scale.PACS numbers: 44.40.+a, 03.50.De The photon heat tunneling between two bodies has attracted much attention in the last decades since it has been predicted that the heat flux (HF) can exceed, at nanoscale, the far field limit set by Planck's black body law by several orders of magnitude [1,2]. This discovery has opened the way to promising technologies for energy conversion and data storage as for example the near-field thermophotovoltaics [3,4] and the plasmon assisted nanophotolitography [5]. This dramatic increase is generally speaking due to the contribution of evanescent modes, which are not accounted for in the StefanBoltzmann law and become only important if the distance between the objects is smaller than the thermal wavelength [6]. The detailed mechanisms which lead to such an enhancement are nowadays for a number of geometries and materials well understood [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] and recent experiments [23][24][25][26][27] have confirmed all theoretical predictions both qualitatively and quantitatively.However, some questions of fundamental importance remain unsolved in complex mesoscopic systems. Indeed, so far, only the HF between two objects [6-9] out of equillibrium has been considered, but how does the heat transport for a collection of individual objects in mutual interaction look like? The collective effects in such many particle systems has not been explored yet, although it is of prime importance for understanding the different heat propagation regimes in disordered systems, determining the thermal percolation tresholds in random nanocomposites structures and studying thermal effects due to the presence of localized modes in such systems.Inside a discrete system of bodies maintained at different temperatures the local thermal fluctuations give rise to oscillations of partial charges which, in turn, radiate their own time dependent electric field in the surrounding medium. These thermally generated fields interact with the nearby bodies and modify through different cross interactions all these primary fields to generate secondary fields which in turn affect the radiated fields and so on. Generally speaking, this problem belongs to the vast category of many-body problems which constitute the theoretical framework of numerous branches of physics (celestial mechanics,condensed matter physics, atomic physics, quantum chemistry). A general th...