Enhancing near-field heat transfer in composite media: Effects of the percolation transition

We investigate the near-field heat transfer between a semi-infinite medium and a nanoparticle made of composite materials. We show that in the effective medium approximation, the heat transfer can be greatly enhanced by considering composite media, being maximal at the percolation transition. Specifically, for titanium inclusions embedded in a polystyrene sphere, this enhancement can be up to thirty times larger than in the case of the corresponding homogeneous titanium sphere. We demonstrate that our findings are robust against material losses, to changes in the shape of inclusions and materials, and apply for different effective medium theories. These results suggest the use of composite media as a new, versatile material platform to enhance, optimize, and tailor near-field heat transfer in nanostructures.

Figure 1

Schematic representation of the system under study.

Figure 2

Mean power absorbed by a polystyrene particle with embedded copper inclusions as a function of frequency and filling factor for a fixed distance between the nanoparticle and the SiC medium and two different values of the depolarization factor, (a) $L=0.1$ $\left(r\simeq 0.3\right)$ and (b) $L=1/3(r=1)$. In both cases, the horizontal dashed lines correspond to percolation threshold $f_c$ predicted by the Bruggeman effective medium theory whereas the vertical dashed lines correspond to the position of plasmon resonance for SiC.

Figure 3

Total power absorbed by the composite particle [normalized by its value for a corresponding homogeneous metallic sphere $P_{\mathrm{abs}}^{\mathrm{total}}(f=1,L,d)\text{]}$ as a function of $f$ for $L=0.1(r\simeq 0.3)$ (blue dashed line) and $L=1/3(r=1)$ (solid red line). The vertical arrows highlight that the values of maximum heat transfer occur precisely at the percolation threshold $f_c$ given by Eq. (3). The other numerical parameters are the same as in Fig. 2.

Figure 4

Contour plot of $P_{\mathrm{abs}}^{\mathrm{total}}$ as a function of both the depolarization factor $L$ and filling factor $f$. The dashed blue curve corresponds to the critical filling factor $f_c$ that determines the percolation threshold for (a) Bruggeman effective medium theory and (b) Lagarkov-Sarychev model. The other numerical parameters are the same as in Fig. 2.