Thermal transport at the nanoscale level is attracting attention not only because of its physically interesting features such as peculiar behavior phonons due to their pronounced ballistic and wave-like properties but also potential applications in alleviating heat dissipation problems electronic optical devices thermoelectric energy harvesting. In last quarter-century, researchers have elucidated thermal various nanostructured materials, including phononic crystals (PnCs): artificial...

Understanding and quantifying the fundamental physical property of coherence thermal excitations is a long-standing general problem in physics. The conventional theory, i.e., phonon gas model, fails to describe its impact on transport. In this Letter, we propose heat conduction formalism supported by theoretical arguments direct atomic simulations, which takes into account both model wave nature phonons. By naturally introducing packets flux from concepts, derive an original conductivity...

The classical Fourier's law fails in extremely small and ultrafast heat conduction even at ordinary temperatures due to strong thermodynamic nonequilibrium effects. In this work, a macroscopic phonon hydrodynamic equation beyond with relaxation term nonlocal terms is derived through perturbation expansion the Boltzmann around four-moment solution. temperature jump flux tangential retardant boundary conditions are developed based on Maxwell model of phonon-boundary interaction. Extensive...

The single mode relaxation time approximation has been demonstrated to greatly underestimate the lattice thermal conductivity of two-dimensional materials due collective effect phonon normal scattering. Callaway's dual model represents a good otherwise ab initio solution Boltzmann equation. In this work we develop discrete-ordinate-method (DOM) scheme for numerical equation under model. Heat transport in graphene ribbon with different geometries is modeled by our scheme, which produces...

The understanding and modeling of inelastic scattering thermal phonons at a solid/solid interface remain an open question. We present fully quantum theoretical scheme to quantify the effect anharmonic phonon-phonon via non-equilibrium Green's function (NEGF) formalism. Based on real-space rate matrix, decomposition interfacial spectral energy exchange is made into contributions from local non-local interactions, which former shown be predominant for high-frequency whereas both are important...

Abstract Thermal transport in amorphous materials has remained one of the fundamental questions solid state physics while involving a very large field applications. Using heat conduction theory incorporating coherence, we demonstrate that strong phase correlation between local and non-propagating modes, commonly named diffusons terminology systems, triggers heat. By treating thermal vibrations as collective excitations, significant contribution diffusons, predominantly relying on further...

In recent times, the unique collective transport physics of phonon hydrodynamics motivates theoreticians and experimentalists to explore it in micro- nanoscale at elevated temperatures. Graphitic materials have been predicted facilitate hydrodynamic heat with their intrinsically strong normal scattering. However, owing experimental difficulties vague theoretical understanding, observation Poiseuille flow graphitic systems remains challenging. this study, based on a microscale platform...

We experimentally demonstrate the enhancement of far-field thermal radiation between two nonabsorbent Si microplates coated with energy-absorbent silicon dioxide (${\mathrm{SiO}}_{2}$) nanolayers supporting propagation surface phonon polaritons. By measuring radiative conductance plates, we find that its values are twice those obtained without ${\mathrm{SiO}}_{2}$ coating. This twofold increase results from hybridization polaritons guided modes inside and is well predicted by fluctuational...

The coherent quantum effect becomes increasingly important in the heat dissipation bottleneck of semiconductor nanoelectronics with characteristic size shrinking down to few nano-meters scale nowadays. However, mechanical model remains elusive for anharmonic phonon-phonon scattering extremely small nanostructures broken translational symmetry. It is a long-term challenging task correctly simulate transport including at relevant practical applications. In this article, we present clarified...

The anomalous thermal conductivity enhancement by defects in resonant structures proves the phonon coupling and provides further freedom for tuning transport.

Nano-phononic crystals have attracted a great deal of research interest in the field nanoscale thermal transport due to their unique coherent behavior. So far, there been many advances theory and simulation studies nano-phononic crystals. In this paper, we summarize state-of-the-art from perspective at low temperatures, minimum conductivity, Anderson localization, various nanosystems, frame machine learning driven studies. Each part is specifically presented under different methodologies,...

Our direct atomic simulations reveal that a thermally activated phonon mode involves large population of elastic wavepackets. These excitations are characterized by wide distribution lifetimes and coherence times expressing particle- wave-like natures. In agreement with simulations, our theoretical derivation yields generalized law for the decay number taking into account coherent effects. Before conventional exponential due to phonon-phonon scattering, this introduces delay proportional...

The understanding and modeling of heat transport across nanometer subnanometer gaps, where the distinction between thermal radiation conduction becomes blurred, remains an open question. In this work, we present a three-dimensional atomistic simulation framework by combining molecular dynamics (MD) phonon nonequilibrium Green's function (NEGF) methods. relaxed atomic configuration interaction force constants metallic vacuum nanogaps are generated from MD as inputs into harmonic NEGF. Phonon...

The Tesla valve benefits the rectification of fluid flow in microfluidic systems

The direct simulation of the dynamics second sound in graphitic materials remains a challenging task due to lack methodology for solving phonon Boltzmann equation such stiff hydrodynamic regime. In this work, we aim tackle challenge by developing multiscale numerical scheme transient under Callaway's dual relaxation model which captures well collective kinetics. Comparing traditional methods, present is efficient, accurate and stable all transport regimes attributed avoiding use time spatial...

The Anderson localization of thermal phonons has been shown only in few nano-structures with strong random disorder by the exponential decay transmission to zero and a conductivity maximum when increasing system length. In this work, we present path demonstrate phonon distinctive features graded superlattices short-range order long-range disorder. A minimum length appears due non-zero constant, which is feature partial caused moderate We provide clear evidence through combined analysis...

We analyze the heat transfer between two metals separated by a vacuum gap in extreme near-field regime. In this crossover regime conduction and radiation, exchanges are mediated photon, phonon, electron tunneling. quantify relative contribution of these carriers with respect to both separation distance bodies applied bias voltage. presence weak (${V}_{\mathrm{b}}<100\phantom{\rule{4pt}{0ex}}\mathrm{mV}$), electrons phonons can contribute equally near contact, while photons becomes...