Superballistic transport of thermal photons in confined many-body systems

Abstract

Ballistic transport, realized when the system size is smaller than the mean free path of energy carriers, is traditionally regarded as the ultimate limit for energy transfer. Here, we predict a superballistic radiative heat transport regime that surpasses this limit in dilute chains of plasmonic nanoparticles confined within cavities. This anomalous regime exhibits superlinear scaling of the effective thermal conductivity (k ~L^1.5) and originates from the amplification of long-range interactions mediated by cavity-guided modes. Our results establish a framework for ultrafast photonic heat transport and open pathways for thermal management, information processing and energy transfer in quantum and nanoscale systems.

Figures (4)

• Figure 1: Sketch of a plasmonic nanoparticle chain in free space, in a planar cavity or in a cylindrical cavity. Reducing the photonic dimensionality strengthens long-range many-body interactions along the chain, enabling the cooperative formation of accelerated guided and radiative modes that drive ballistic and superballistic transport.
• Figure 2: Radiative transport along a chain of $N = 10{,}001$ SiC nanoparticles in free space or confined in planar or cylindrical cavity. (a) Spatial scaling of the thermal conductance $G$ between the central NP and other NPs at position $z$ (symbols), shown for chains with different lattice constants $\Lambda$; for comparison, $G$ between two isolated NPs is plotted as solid lines. (b) Transmission coefficient $\mathcal{T}_{ij}$ between NPs at various separations $z$ for a chain with $\Lambda = 0.2\,\upmu\mathrm{m}$. Insets display the spatial distribution of the electric component of the local density of states of electromagnetic field when only the central NP is thermally excited.
• Figure 3: Dispersion relations obtained via eigenfrequency mapping for SiC nanoparticle chains with interparticle spacing $\Lambda = 0.2~\upmu\mathrm{m}$ and total length $L = 10^4~\upmu\mathrm{m}$ ($N = 50{,}001$) in (a) free space, (b) planar cavity and (c) cylindrical cavity. Here, T denotes the transverse modes ($x$- and $y$-polarized excitations) and L the longitudinal mode ($z$-polarized excitation). The insets show the normalized group velocity $v_{\mathrm{g},k}/c$ and the propagation length $\xi_k$ near the light line and within the coupling region. (d) Distribution of the fast eigenmodes for chains of varying lengths.
• Figure 4: Scaling of the effective thermal conductivity $\kappa_{\text{eff}}$ at $T=300\,K$ of free and confined SiC nanoparticle chains ($R=25\,\mathrm{nm}$) with lattice constant $\Lambda=0.2\upmu$m versus the chain length $L$. The gap size of the planar cavity is $h=1\,\upmu\mathrm{m}$ and the diameter of cylinder is $D=7\,\upmu\mathrm{m}$. Inset: temperature profiles along the chains in steady state regime.