Nonreciprocal Thermal Material by Spatiotemporal Modulation

Abstract

The thermal properties of a material with a spatiotemporal modulation, in the form of a traveling wave, in both the thermal conductivity and the specific heat capacity are studied. It is found that these materials behave as materials with an internal convectionlike term that provides them with nonreciprocal properties, in the sense that the heat flux has different properties when it propagates in the same direction or in the opposite one to the modulation of the parameters. An effective medium description is presented which accurately describes the modulated material, and numerical simulations support this description and verify the nonreciprocal properties of the material. It is found that these materials are promising candidates for the design of thermal diodes and other advanced devices for the control of the heat flow at all scales. DOI: 10.1103/PhysRevLett.120.125501 The research on materials with nonreciprocal thermal properties has received a great amount of attention in recent years. These materials have different propagation of thermal energy along two opposite directions. With the socalled thermal diode being the most immediate application of these structures [1], other devices and applications are easily envisioned, like thermal transistors and even logic circuits [2]. Nonreciprocal materials have been properly studied theoretically and experimentally at different scales [3][4][5][6], and it has been demonstrated that the realization of a nonreciprocal material requires the use of a combination of nonlinear and asymmetric structures [7]. However, the realization of nonreciprocal materials based on nonlinear elements limits their applicability, since nonlinearity does not occur at all temperatures and scales, so that we find that the rectification properties of the materials are efficient in only a short range of temperatures.In this context, metamaterials, which are artificially structured materials with a priori-designed properties, have overcome one of the major drawbacks of common materials, since their properties depend on the internal artificial structure and not on intrinsic properties of the constituent materials, which in turn allows us to decide at which scale, frequency, or temperature range we want to operate [8].Here, a special type of metamaterial is employed presenting nonreciprocal properties, which consists of a material where the thermal properties are functions of both space and time in a wavelike fashion. This special type of modulation has been studied in elastic and acoustic materials [9][10][11][12], whose nonreciprocal properties for the propagation of waves have been widely demonstrated. We will apply these ideas to the diffusion equation describing thermal waves in solids, and nonreciprocal thermal transport will be found.

Effective medium concept in temporal metamaterials

“…However, to further control wave propagation at will, there is another dimension, time (t), that can be manipulated in addition to these three dimensions. Space-time metamaterials have been studied since several decades ago [32,33] and they have recently been used for exciting applications [34,35] such as inverse prism [36], frequency conversion [37], nonreciprocity [38][39][40], temporal band-gap, and time reversal [41][42][43][44][45][46][47][48]. The idea of "time crystals" has also been introduced and developed [49][50][51][52].…”

Nonreciprocal acoustic transmission in cascaded resonators via spatiotemporal modulation

“…Recently, non-reciprocal devices based on spatiotemporal modulation have gained significant research interest in different physical systems 2,[13][14][15][16][17][18][19][20][21][22][23] . Time reversal symmetry is broken in time-modulated systems and therefore nonreciprocity can be achieved.…”

Nonreciprocal thermal and thermoelectric transport of electrons in noncentrosymmetric crystals

“…Unlike the electric current, the heat current is carried by any elementary excitations in materials. The nonreciprocal thermal transport has been studied for each carrier, such as phonons [5][6][7][8][9] and photons 4,10 . However, in this paper, we focus only on the thermal transport carried by the electrons in crystals.…”