Radiative Bistability and Thermal Memory
Résumé
We predict the existence of a thermal bistability in many-body systems out of thermal equilibrium which exchange heat by thermal radiation using insulator-metal transition materials. We propose a writing-reading procedure and demonstrate the possibility to exploit the thermal bistability to make a volatile thermal memory. We show that this thermal memory can be used to store heat and thermal information (via an encoding temperature) for arbitrary long times. The radiative thermal bistability could find broad applications in the domains of thermal management, information processing, and energy storage. The control of electric currents with diodes and transistors is undoubtedly a cornerstone in modern electronics which has revolutionized our daily life. Astonishingly, similar devices which allow for controlling the heat flow are not as widespread as their electronic counterparts. In 2006, Li et al. [1] proposed a thermal analog of a field-effect transistor by replacing both the electric potentials and the electric currents in the electronic circuits by thermostats and heat fluxes carried by phonons through solid segments. A few years later, several prototypes of phononic thermal logic gates [2] as well as thermal memories [3,4] have been developed from these basic building blocks allowing for processing information with heat currents rather than with electric currents. However, this phonon-based technology is intrinsically limited by the speed of the heat carriers, the acoustic phonons, and by the presence of Kapitza resistances between the basic solid elements. Moreover, because of radiative losses and thermal fluctuations, the temporal stability of these systems is limited and a frequent refreshing is needed. To overcome these problems, optical con-tactless analogs of some basic devices such as the radiative thermal diode [5,6] and the radiative transistor [7] have recently been introduced. However, some functionalities are, to date, missing to allow for an all-photonic treatment of heat fluxes. In this Letter, we make a step forward in this direction by introducing the concept of a radiative thermal memory which is able to store information for an arbitrary long time using thermal photons. To do so, we first demonstrate the existence of bistable thermal behavior in simple systems consisting of two membranes which are out of thermal equilibrium and which are further sandwiched between two thermal baths at different temperatures. The existence of multiple equilibrium temperatures requires [3] the presence of negative differential thermal resistances. However, as shown by Fan and co-workers [8], this is not at all a sufficient condition. As we will show, the thermal bistability mechanism can only exist in many-body systems [9–11]. Finally, as a direct consequence, we show that the bistability can be used to store one bit of thermal information. While, in a conventional electronic memory, the states 0 and 1 are defined by two different applied voltages for which the electric current inside the circuit is 0, its thermal counterpart is defined with distinct equilibrium temperatures which lead to vanishing heat fluxes between the different parts of the system. Let us consider a system as depicted in Fig. 1 composed by two parallel homogeneous membranes of finite thicknesses δ 1 and δ 2 and separated by a distance d. The left (right) membrane is in contact with a thermal bath having temperature T L (T R), where T L ≠ T R. In a practical point of view, the field radiated by these baths can be produced by
Domaines
Optique [physics.optics]
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