Near-Field Thermal Transistor

Abstract : 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. The electronic solid-state transistor [Fig. 1(a)] introduced by Bardeen and Brattain in 1948 [1] is undoubtedly the cornerstone of almost all modern systems of information treatment. The classical field-effect transistor (FET), which is composed of three basic elements, the drain, the source, and the gate, is basically used to control the flux of electrons (the current) exchanged in the channel between the drain and the source by changing the voltage applied on the gate. The physical diameter of this channel is fixed, but its effective electrical diameter can be varied by the application of a voltage on the gate. A small change in this voltage can cause a large variation in the current from the source to the drain. In 2006, Li et al. [2] proposed a thermal counterpart of FET by replacing both the electric potentials and the electric currents by thermostats at a fixed temperature and heat fluxes carried by phonons through solid segments. Later, several prototypes of phononic thermal logic gates [3] as well as thermal memories (see [4] and references therein) were developed in order to process information by phonon heat flux rather than by electric currents. However, this technology suffers from some fundamental weaknesses which intrinsically limit its performance. One of the main limitations probably comes from the speed of acoustic phonons (heat carriers), which is 4 or 5 orders of magnitude smaller than the speed of photons. Another intrinsic limitation of phononic devices is related to the inevitable presence of local Kapitza resistances. Those resistances which come from the mismatch of vibrational modes at the interface of different elements can reduce the heat flux dramatically. Finally, the strong nonlinear phonon-phonon interaction mechanism makes the phononic devices difficult to deal with in the presence of a strong thermal gradient. On the contrary, the physics of transport mediated by photon tunneling remains unchanged close and far from thermal equilibrium. This explains, in part, why so many efforts have been deployed, during the past decades, to attempt to develop full optical or at least optoelectronic architectures for processing and managing information. In particular, important developments have been carried out during the past decade with plasmonics systems [5,6] to greatly increase the speed of information processing while reducing the dimension of devices at the nanoscale at the same time. However, despite these major steps forward, an optical transistor is still missing. We introduce here a thermal transistor [Fig. 1(b)] based on the heat transport by evanescent photons rather than by acoustic waves or electrons. This near-field thermal transistor (NFTT) basically consists of a gate made of an insulator-metal transition (IMT) material which is able to qualitatively and quantitatively change its optical properties through a small change of its temperature around a critical temperature T c. Vanadium dioxide (VO 2) is one of such materials (the choice of IMT depends on the operating range of the transistor: around T ¼ 500 K, LaCoO 3 could replace VO 2 , for instance) that undergoes a first-order transition (Mott transition [7]) from a high-temperature metallic phase to a low-temperature insulating phase [8] close to room temperature (T c ¼ 340 K). Different works have already shown [9–11] that the heat flux exchanged at close separation distances (i.e., in the near-field regime) between an IMT material and another medium can be modulated by several orders of magnitude across the phase transition of IMT materials. Further radiative thermal diodes have been recently conceived allowing for
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Physical Review Letters, American Physical Society, 2014, 112 (4), pp.044301. 〈10.1103/PhysRevLett.112.044301〉
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Philippe Ben-Abdallah, Svend-Age Biehs. Near-Field Thermal Transistor. Physical Review Letters, American Physical Society, 2014, 112 (4), pp.044301. 〈10.1103/PhysRevLett.112.044301〉. 〈hal-01335098〉

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