At cryogenic temperatures, thermal transport is predominantly governed by long-wavelength acoustic phonons with exceptionally long intrinsic mean free paths, leading to significant departures from the diffusive transport behavior characteristic of room temperature. Understanding these transport mechanisms is essential for emerging technologies, including quantum computing, cryogenic electronics, and aerospace systems. This review summarizes the fundamental physics governing phonon-mediated thermal transport in the cryogenic regime. We first introduce the classical Casimir-Knudsen framework for geometry-limited transport and then discuss how this picture is modified by reduced dimensionality, competing scattering mechanisms, collective phonon transport, and wave effects. Particular emphasis is placed on the physical origins of thermal-conductivity behaviors that deviate from the conventional T³ scaling. We further examine the implications of cryogenic phonon transport for self-heating and thermal management in electronic and quantum devices. Finally, we identify key unresolved questions, particularly regarding predictive modeling and thermal management in cryogenic quantum devices. By providing a unified overview of recent advances, this review aims to stimulate further progress in the fundamental understanding and engineering of thermal transport at cryogenic temperatures.

Directional heat spreading enabled by intrinsic thermal conductivity (κ) anisotropy offers a promising route to address thermal bottlenecks in integrated circuits. Here, we demonstrate atomic-level engineering of anisotropic thermal transport in C₂₄ monolayers through atomic spatial arrangement. Based on the high-accuracy neuroevolution potential (NEP)-empowered multiscale simulations, we systematically investigate the lattice thermal transport properties of quasi-tetragonal phase (qTP) and quasi-hexagonal phase (qHP) C₂₄ monolayers with distinct atomic arrangements. The results show that qTP C₂₄ exhibits relatively higher and nearly isotropic κ. In contrast, the qHP C₂₄ displays pronounced in-plane κ anisotropy, with a room-temperature anisotropy ratio of κ_y/κ_x ≈ 1.7. In-depth phonon transport analysis shows that direction-dependent acoustic transport and the substantial participation of low-frequency optical modes are responsible for the intrinsic κ anisotropy. Furthermore, orbital-projected electronic structures reveal a distinct p_x and p_y orbital splitting in qHP C₂₄, indicating anisotropic orbital hybridization, which fundamentally underlies its intrinsic κ anisotropy. Device-level finite-element simulations further confirm that atomic-spatial-arrangement induced anisotropic thermal transport enables directional heat spreading and thermal crosstalk regulation. The findings in this study establish atomic-level design as an external-field-free strategy for engineering anisotropic thermal transport.

Cu₂SnSe₃ exhibits exceptionally low lattice thermal conductivity (κ_L) and a nonclassical temperature dependence among ternary copper-based diamondoid compounds, yet the microscopic origins of these phonon behaviors remain poorly understood. In this work, we theoretically investigate the intrinsic phonon transport in Cu₂SnSe₃ by employing a two-channel thermal transport model that separates particle-like (κ_p) and coherent contributions (κ_c), while fully incorporating both three-phonon (3ph) and four-phonon (4ph) scattering processes. Our calculations show that κ_c is negligible at 300 K but becomes progressively more significant at elevated temperatures, while κ_p remains the dominant contributor to κ_L over the entire temperature range. 4ph scattering is identified as the primary factor driving the deviation from the classical T^-1 dependence, yielding a temperature scaling of T^-1.1 that closely matches the experimental T^-1.2 behavior. This strong 4ph scattering originates from flat optical phonon modes in the 1.2-2.2 THz range, which provide an exceptionally large scattering phase space. The low κ_L (e.g., ~ 0.8 W m^-1 K^-1 at 773 K) of Cu₂SnSe₃ relative to other ternary copper-based diamondoid compounds is attributed to the asymmetric potential energy of Cu atoms, which induces large atomic displacement parameters and pronounced anharmonicity in the Cu-related low-frequency optical branches. Furthermore, qualitative analyses of cation disorder and anion substitution show that disorder leads to significant phonon broadening, while replacing Se with S hardens the acoustic branches and markedly shifts the optical modes upward. Our findings not only clarify the origins of the nonclassical temperature dependence and low κ_L in Cu₂SnSe₃, but also provide a general guideline for designing diamondoid thermoelectrics with intrinsically suppressed κ_L.

Layered chalcogenides X₂PdY₆ (X = Nb, Ta; Y = S, Se) offer tunable properties for energy conversion and electronic applications, yet their intrinsic lattice thermal transport remains poorly understood. Here, we develop neuroevolution potentials and use molecular dynamics to investigate phonon-mediated heat transport in ideal bulk and few-layer X₂PdY₆. At 300 K, the bulk crystals exhibit strong anisotropy, with the highest lattice thermal conductivity (LTC) along the in-plane [010] direction and the lowest along the cross-plane [102] direction. The corresponding anisotropy ratios are 10.4, 8.1, 14.3, and 9.0 for Nb₂PdS₆, Nb₂PdSe₆, Ta₂PdS₆, and Ta₂PdSe₆, respectively. Within each layer, LTC along [20$\overline{1}$] is lower than along [010] because the longer structural period and asymmetric X-Y bonding enhance anharmonicity. Variations in bond strength and atomic mass produce the composition-dependent ordering κ_Nb2PdS6 > κ_Ta2PdS6 > κ_Nb2PdSe6 > κ_Ta2PdSe6. Exfoliation increases the in-plane LTC and reduces its anisotropy by preferentially enhancing low-frequency phonon transport along [20$\overline{1}$]. Below 2 THz, monolayer phonon mean free paths are 5-8 times longer than those in the corresponding bulk crystals. These results establish the intrinsic LTC trends and dimensional crossover in X₂PdY₆, providing a microscopic basis for controlling anisotropic phonon transport in layered chalcogenides.

Barocaloric materials have attracted considerable attention as promising thermal-management alternatives to conventional vapour-compression technologies; however, virtually all reported systems exhibit only a single type of barocaloric effect (BCE), fundamentally constraining the functional versatility and accessible operating-temperature range of prospective devices. Here we report that two fluorinated alcohols, C₉H₆F₁₄O₂ (2OH) and C₉H₄F₁₆O (1OH), harbour two mechanistically distinct phase transitions within a single material family: a solid-solid transition giving rise to a conventional normal BCE, and a solid-liquid transition yielding a rare inverse BCE. By systematically tuning the number of hydroxyl substituents (-OH), the transition temperatures of these two processes can be shifted by several tens of kelvin, enabling their natural alignment with distinct low- and high-temperature operating regimes. This intrinsic thermal property allows both heating and cooling functions to be realized within the same material system, solely through the exploitation of its barocaloric characteristics. Remarkably, 1OH exhibits exceptional pressure sensitivity during solid-liquid transition, reaching 0.34 K/MPa at 100 MPa. These findings establish fluorinated alcohols as a versatile and high-performance material platform, and open new avenues for the rational design of next-generation barocaloric energy conversion technologies.

Understanding the interplay between magnetic ordering and phonon thermal transport is crucial for the thermal management of two-dimensional magnetic devices. Here, using first-principles calculations combined with the phonon Boltzmann transport equation, we systematically investigate the lattice thermal transport properties of four-layer CrSBr during its layer-by-layer magnetic switching process. As the magnetic configuration evolves from the antiferromagnetic (AFM) state to the ferromagnetic (FM) state through successive spin reversals, the lattice thermal conductivity exhibits a pronounced nonmonotonic variation. In particular, the intermediate first ferrimagnetic (FiM1) state shows a dramatic reduction in thermal conductivity of approximately 37.2% along x and 54.5% along y compared with the AFM state, whereas the second ferrimagnetic (FiM2) and FM states retain thermal conductivities close to the AFM configuration. Detailed analysis reveals that magnetic switching only weakly affects harmonic phonon properties, including phonon dispersions and group velocities. In contrast, the FiM1 state exhibits strongly enhanced anharmonic phonon scattering and reduced phonon participation ratios in the low-frequency region dominated by heat-carrying phonons. Further layer-resolved vibrational analysis identifies a mixed vibrational character in the FiM1 state, combining AFM-like layer-selective and FM-like layer-equivalent features, which is correlated with enhanced low-frequency anharmonic phonon scattering. Our results reveal a unique mechanism for magnetically tunable thermal transport in van der Waals magnets and provide microscopic insights into magnetic-order-dependent phonon thermal transport in layered magnetic materials.

Hydrodynamic electron transport, in which electrical transport in solids resembles fluid hydrodynamics when momentum-conserving electron-electron scattering dominates, has attracted much attention over the past decade. However, its thermal aspects have received considerably less attention. In this paper, we systematically simulate electron transport in a graphene Corbino disk by solving the steady-state Boltzmann transport equation with a dual-relaxation-time Callaway model, in which momentum-conserving and momentum-relaxing scatterings are explicitly distinguished. By varying the magnetic field strength and scattering rates, we compare the charge and heat flux responses across the diffusive-to-hydrodynamic crossover under both electric-field and temperature-gradient driving. We show that magnetic-field-induced deflection of both fluxes is strongly enhanced in the hydrodynamic regime but nearly suppressed in the diffusive regime. Under electric-field driving, a pronounced temperature rise is observed in the hydrodynamic regime due to reduced dissipation, while the diffusive regime remains nearly isothermal. Under temperature-gradient driving, the deflection exhibits the opposite chirality to that in the electric-field case. These findings establish that thermal transport can provide a sensitive and independent diagnostic of electron hydrodynamics, and identify the magnetic field as an effective discriminator between collective and dissipative conduction.

The precise evaluation of real-world thermoelectric cooling (TEC) performance is vital for both the development of TEC devices and the rational design of TEC materials. Due to the relatively limited temperature difference (ΔT) that a single-stage TEC can achieve, the classical analytical formulae for thermoelectric cooling are commonly used with averaged material properties in the cooling performance evaluation. Nevertheless, this could cause remarkable errors in evaluations of the cooling power, even under a ΔT as low as 10 K. In this work, a cumulative model for thermoelectric cooling is proposed to evaluate the maximum coefficient of performance (COP) as well as the maximum cooling power of a TEC device under finite temperature differences, with the temperature dependence of material properties being fully considered. The inherent deficiencies in predicting the maximum cooling power by both the classical formulae and the original cumulative model are identified, and effective refinements are implemented to reduce the prediction error. Eight thermoelectric materials with state-of-the-art ZT values near room temperature are assessed for electronics cooling scenarios within a cold side temperature (T_c) range of 300-350 K. In comparison to the classical formulae, the proposed model predicts the maximum COP with comparably satisfying accuracies (±2%), while significantly improves the prediction accuracy of the maximum cooling power from approximately ±30% to within ±5% over a ΔT range of 10-70 K. This work fills the gap between thermoelectric material properties and device-level cooling performance, and is beneficial to the development and application of thermoelectric conversion technology for cooling purposes.

Thermal transport at the nanoscale is fundamentally important and crucially impacts a range of applications from electronic chip cooling to advanced energy technology. Inspired by the rise of twistronics, twist engineering has recently emerged as a powerful approach to control nanoscale heat flow, which leverages interlayer rotation in van der Waals materials as a new degree of freedom. Here, we first briefly introduce the basic principles of twist engineering. Subsequently, we discuss various experimental techniques and computational approaches for investigating phonon-mediated heat conduction, together with key results and physical mechanisms for the active manipulation of both out-of-plane and in-plane transport. Furthermore, we review advances in the twist-induced modulation of photon-mediated thermal radiation, distinguishing strategies that tune intrinsic optical responses from those utilizing extrinsic couplings. We conclude with remarks on the opportunities and challenges for future exploration of twist-engineered thermal management and energy conversion.

Thermal routing refers to the ability to direct heat energy from a source to a selected drain, offering great potential for asymmetric thermal path regulation. However, existing approaches to asymmetric heat transport largely rely on phononic band engineering and mechanically moving components, typically limited to heat fluxes at the microwatt level or complicated experimental configurations with long-term reliability concerns. Herein, inspired by the analogy between thermal advection and thermoelectric effects in dragging heat energy, we propose a solid-state thermal metadevice featuring large heat energy flux and near-unity thermal split ratio. By examining the evolutionary path of the Seebeck coefficients, the unique asymmetry-enhancement mechanism arising from the commonly-overlooked Thomson effect is revealed, enabling an improved thermal splitting effect of the device. Free of mechanically moving components, this work provides a new paradigm for the design of solid-state thermal routers with great power and electrical reconfigurability. It makes a promising candidate for compact thermal management and thermal logic processing where asymmetric time-varying heat energy reallocation matters.

High-heat-flux chips in high-performance computing, heterogeneous integration, and wide-bandgap electronics are reaching a thermal-management ceiling: transistor-scale hotspots, dense stacks, and low-conductivity interlayers force heat through resistive, interface-rich paths before it reaches the coolant. Microfluidic cooling can support 10²-10³ W/cm² heat fluxes and higher local loads, yet it is often framed as a competition among microchannels, jets, manifolds, two-phase structures, and high-conductivity spreaders. This review reconstructs the field through thermal-path compression and bottleneck migration, using cooling-boundary location, compressed resistance segment, and residual limit as organizing axes. As cooling advances from package-integrated schemes to embedded/interposer and near-junction architectures, the dominant limit shifts from package-side conduction to hotspot spreading, solid–solid/solid–liquid interfacial resistance, hydraulic allocation, and confined phase instability. Representative architectures are assessed through heat flux, pressure drop, area-normalized thermal resistance, and evidence maturity, emphasizing that record heat flux is not transferable without defined heated area, temperature criterion, coolant state, hydraulic cost, and device boundary. We further distinguish proof-of-concept thermal vehicles from device-relevant, package-compatible, and deployment-oriented platforms by considering manufacturability, sealing and leakage risk, semiconductor-process compatibility, coolant/material compatibility, and scale-up to large-area or multi-chip systems. Interface engineering and diamond-enabled platforms show that high intrinsic conductivity is useful only through reliable, low-resistance, and manufacturable interfaces. This framework recasts microfluidic cooling as near-junction co-design rather than a heat-flux race.

Carbon fibers (CF)/epoxy composites are widely utilized in aerospace and transportation due to their light weight and high specific strength/modulus. However, poor interfacial binding between CF and the epoxy matrix leads to phonon scattering and inefficient load transfer, causing heat accumulation and reduced service life in high-power electronic systems. In this study, CF was coated with a styrene, benzocyclobutene, and methyl methacrylate units containing polymer layer mixed with carbon nanotubes (CNT) through impregnation and drying. The polymer layer was then thermally crosslinked to obtain the polymer and CNT coated CF (CF@(CNT/P)). CF@(CNT/P) was then applied as reinforced fibers and epoxy resin containing a liquid crystal structure as the matrix to prepare CF@(CNT/P)/epoxy composites. The π-π interactions and hydrogen bonds between CF and epoxy resin were enhanced by the benzene ring and ester groups in the polymer, thereby improving the interfacial binding between epoxy resin and CF. CF@(CNT/P)/epoxy composite showed enhanced load-bearing and thermal conduction performance. When the mass fractions of CNT and copolymer in CNT/P/dichloromethane (DCM) solution were 0.03 wt% and 0.1 wt%, respectively, the CF@(CNT/P) had the best interfacial binding to the epoxy resin. The interlaminar shear strength and flexural strength of the CF@(CNT/P)/epoxy composite increased from 23.7 and 252.5 MPa of CF/epoxy composite to 31.4 and 369.1 MPa, respectively. Meanwhile, the in-plane (λ_∥) and through-plane (λ_⊥) thermal conductivity values were improved from 7.15 and 0.31 W/(m·K) of CF/epoxy composite to 10.08 and 0.58 W/(m·K), respectively. The CF@(CNT/P)/epoxy composite also demonstrated an electromagnetic interference shielding effectiveness of 38.6 dB which has broad application in high-power electronic information systems.

Deep eutectic solvent (DES) based nanofluids have gained ample attention owing to their extraordinary thermophysical properties such as wide temperature range and thermal stability. While poor static stability of DES based nanofluids heavily hinders their practical application due to the incompatibility with dispersants. Herein, a novel zinc oxide (ZnO) nanofluids using ethylene glycol and potassium acetate DES for solar thermal utilization were developed. With the aim of addressing the poor stability, a one-step in situ synthesis involving microwave-induced dehydration was employed to prepare self-dispersing ZnO nanoparticles without external dispersants. Thermophysical properties and photothermal performance of nanofluids with varying mass fractions (0.5-5 wt.%) were systematically investigated. Results indicate that ZnO inclusion significantly improves thermal conductivity and photothermal conversion. Specifically, the 5 wt.% sample exhibited a 12% increase in thermal conductivity at 65 °C compared to the base fluid, while the 0.5 wt.% sample demonstrated optimal photothermal response under low light intensity. Additionally, the fluids displayed anomalously enhanced specific heat capacity (up to 14.6%), attributed to the formation of ordered interfacial liquid layers on the high-surface-area ZnO nanoparticles through electrostatic interactions and hydrogen bond rearrangement, offering dual advantages in heat transfer and storage, while maintaining dispersion stability for approximately two weeks, which thus presents a low-cost, stable, and environmentally friendly strategy for developing heat transfer fluids suitable for medium-to-high temperature solar collection systems.

Two-dimensional (2D) heterostructures provide an unusually versatile platform for engineering interfaces at the atomic scale. As these materials move toward electronic, optoelectronic and multifunctional devices, heat flow across their interfaces is emerging as a central factor that governs performance, stability and reliability. Interfacial thermal transport has traditionally been treated as a material-pair-specific conductance that should be measured and optimized. In 2D heterostructures, however, the interface is not a passive boundary with a fixed thermal response. Its conductance is shaped by the structural history, local configuration and dynamic state of the interface. In this perspective, we discuss how interface formation, thermal metrology and microscopic phonon mechanisms together define heat flow across atomically thin heterointerfaces. We highlight how direct growth and transfer assembly create distinct opportunities for lateral and vertical interfaces, how Raman thermometry, pump-probe thermoreflectance and electrical methods quantify interfacial transport, and how elastic transmission, inelastic scattering and interface-specific vibrational states govern nanoscale heat flow. We then consider how intrinsic and external control of 2D heterointerfaces can be used to tune conductance for heat dissipation, local heat confinement, rectification and thermal switching. We argue that the future of the field lies in moving from passive characterization of interfacial thermal conductance toward predictive, spatially resolved and actively controlled heat flow in 2D heterostructures.

Imaging thermal properties at the microscale is crucial for unveiling the structure-property relation and developing next-generation thermal management materials. Here, we apply a frequency-domain thermoreflectance (FDTR) microscopy for imaging the thermal conductivity and interfacial thermal conductance of thermal interface materials (TIMs). A fixture customized for imaging thermal properties of TIMs is developed, where the sample is sandwiched between a silica slide coated with a metal transducer and a substrate wafer, and the thermal transport properties are extracted using a bidirectional thermal model. The thermal conductivity of TIMs loaded with thermally conductive particles is profiled with micrometer resolution, and significant local non-uniformity is observed. Pressure-dependent FDTR imaging during loading and unloading reveals the local redistribution of conductive filler particles. Correlative micro-computed tomography reveals that the high thermal conductivity regions correspond to the aggregation of thermally conductive particles. Further statistical analysis of the FDTR image unveiled the asymmetrical and long-tailed probabilistic distribution of thermal conductivity values. Through statistical modeling, we demonstrate that this asymmetry originates from the lognormal size distribution of microparticles. Our work sheds light on the structure-property relation between microstructure and thermal conductivity distribution of TIMs at the microscale.

Supercooling perfusion extends organ-preservation time by maintaining grafts ice-free below 0 °C, but thermal non-uniformity and limited intra-organ temperature observability hinder protocol design, especially at large-organ scales. We developed an anatomically based thermo-fluidic modeling framework for supercooled perfusion of the liver, heart, and kidney in a recirculating multi-organ configuration and validated the model experimentally. Three-dimensional organ geometries from the BodyParts3D repository were combined with a porous-media tissue representation and realistic perfusion boundary conditions to resolve transient intra-parenchymal temperature fields. A self-developed variable-frequency supercooled machine perfusion (MP) platform was used to measure temperatures in porcine livers, hearts, and kidneys using multiple thermocouples placed at anatomically corresponding locations. Simulated temperature trajectories agreed with measurements across organs, with mean absolute errors of 0.24 °C for the liver, 2.63 °C for the heart, and 0.4 °C for the kidney, and reproduced initial cooling followed by progressive approach to the perfusate temperature and stabilization. Spatial temperature maps captured organ-specific gradients consistent with convective heat extraction by perfusate delivery and conductive transport within tissue. Using the validated model, we performed parametric sweeps of the inlet perfusion parameter, perfusate thermophysical properties, and external convective heat-transfer coefficient to quantify their effects on cooling rate and temperature uniformity. Based on quantitative metrics, these parameters were found to influence cooling rate and intra-organ temperature uniformity to different degrees, while the magnitude of improvement differed among organs due to size and vascular characteristics. This study provides a validated, under the tested conditions, tool to predict intra-organ temperature evolution and a guide for thermodynamically optimizing supercooled MP protocols in multi-organ preservation.

Anomalous cooling or heating implies attractive underlying thermal physics, and the Mpemba effect and its inverse are typical examples. Most existing explanations for such phenomena are based on microscopic Markovian models that quantify relaxation using distance measures such as total variation distance or Kullback‑Leibler divergence. Here, we propose a macroscopic network system to observe and analyze the Mpemba effect and its inverse by connecting a thermoelectric module with a body and a reservoir at different initial temperatures. Normal cooling and anomalous cooling can be switched in such a setup, and oscillatory behaviors of temperature, current, and heat flow are found to be the key for achieving the Mpemba effect and its inverse. With an unambiguous definition of the criteria, the occurrence domain of the Mpemba effect is sketched in terms of initial temperature, thermoelectric Figure-of-Merit, and the inductance. This work provides a macroscopic network system to understand the Mpemba effect, and offers a more flexible and dynamic way for thermal management and energy conversion.

Hydrogen is widely recognized as the leading green energy carrier of the 21st century, owing to its diverse production pathways, high combustion energy density, and environmentally benign byproduct: water. However, its wide flammability range (4-75 vol.% in air) and extremely low minimum ignition energy (0.02 mJ) pose significant safety risks across the entire lifecycle of production, storage, transportation, and utilization, necessitating real-time monitoring through highly reliable sensing technologies. Among various hydrogen detection methods, thermal conductivity sensors have attracted considerable attention due to their oxygen-independent operation, broad measuring range, mechanical robustness, and long service lifespan. Despite growing research interest, there remains a notable lack of comprehensive review articles specifically dedicated to thermal conductivity hydrogen sensors (TCHSs) that consolidate the current state of knowledge and guide future research directions. This paper presents a systematic analysis of the working principles and operating modes of TCHSs, introduces key performance parameters, and reviews theoretical models describing the effective thermal conductivity of gas mixtures. The discussion covers representative sensor architectures, gas inlet configurations, and critical environmental factors influencing sensor performance. Furthermore, recent advances and emerging trends are examined, with particular emphasis on smart gas sensing technologies enabled by sensor integration and advanced machine learning algorithms. This study aims to serve as a comprehensive academic reference, offering a clear and structured framework for researchers, particularly those newly entering the field of hydrogen sensing.

Thermal Hall effect (THE) refers to the phenomenon whereby, in a magnetic field, when a longitudinal heat current flows through a material, the heat carriers are deflected, thereby generating a transverse temperature difference between the two lateral edges. The transition from electrical to thermal transport enables this effect to involve a wide range of carriers, thereby providing a unique perspective for investigating complex quantum states in condensed matter physics. THE is increasingly becoming a powerful probe of neutral excitations in materials and is used to explore multifield control phenomena in magneto-thermal-electrical coupled systems. Advances in the field of THE have significantly advanced the study of condensed matter systems under extreme conditions (low temperatures and strong magnetic fields) and have laid the groundwork for exploring novel magneto-thermal-electrical effects in quantum materials. This review systematically reviews recent theoretical and experimental progress on THE, with particular attention to the underlying heat carriers. Through an in-depth analysis of the transport mechanisms of different carriers, quantum material systems that can be used to investigate multicarrier coupled transport are identified, which will significantly facilitate the synergistic control of magneto-thermal-electrical transport in complex interacting systems. Finally, we propose a novel in situ, multiparameter integrated characterization method that enables simultaneous and precise measurement of magnetic, thermal, and electrical parameters on the same micro/nanoscale samples. This approach not only overcomes the limitations of bulk materials but also serves as a key experimental platform for revealing the mechanisms of multicarrier coupled transport in micro/nano samples.

This work investigates the transport of an electron bubble near the free surface of superfluid ³He-B under applied electric and magnetic fields. Based on a theoretical framework combining the quasiclassical Green’s function and the Lippmann–Schwinger equation, we have calculated the scattering cross section and mobility of the electron bubble, together with their temperature and depth dependences. An electric field shifts the position of the electron bubble and thereby tunes its coupling to the surface bound states. The surface density of states decays with depth, whereas the transport cross section increases with energy and depth; these competing trends compensate, resulting in a nearly depth-independent mobility consistent with the linear dispersion of the surface states. In contrast, an applied magnetic field opens a Zeeman gap in the surface-state spectrum, which breaks the linear dispersion of the bound states. Our results demonstrate that external electric and magnetic fields provide effective control of the spectral structure and scattering properties of the surface bound states.

Driven by the escalating chip-level heat flux demands of artificial intelligence and high-performance computing, thermal management has emerged as a critical bottleneck for next-generation microelectronic integration. To address the prominent contradiction between the limited space and the high heat flux in silicon interconnect fabric chips, this research has overcome the key challenge of miniaturizing traditional spray cooling by designing and implementing an ultra-thin spray cooling heat sink embedded in a silicon-based test chip. The core advancement stems from a synergistic integration of topology-optimized micro-nozzle architecture and silicon-based microfabrication, achieving a total spray module thickness of merely 3.5 mm and enabling uniform near-field atomization from four nozzles under low pressure. Experimental results demonstrate that the heat sink removes 614 W at a junction temperature of 92 °C from a compact footprint of 9.5 mm × 9.5 mm, yielding a peak surface heat transfer coefficient of 9.03 W/(cm²·K). This performance not only validates the feasibility of spray cooling in ultra-thin packaging architectures, but also presents one of the first experimental demonstration of the monolithic integration of a spray cooling system with a silicon-based integrated circuit. This work establishes a viable pathway for ultra-high heat flux thermal management under extreme spatial constraints, enabling the practical deployment of spray cooling in high-power-density electronics, including high-performance computing and artificial intelligence chips.

Effective thermal management is crucial for global sustainability, yet it faces a fundamental challenge: traditional materials cannot dynamically regulate the three coupled heat transfer modes, namely conduction, convection, and radiation, in complex, real-world environments. To overcome this, we present a paradigm shift from material selection to the architectural design of synergistic heat transfer. This perspective explores how multimodal thermal metamaterials, through engineered microstructures and topology, enable programmable control over coupled thermal flows. We highlight how this approach yields advanced functionalities, including directional guidance, adaptive cooling, and waste-heat recovery, across scales ranging from microelectronics to buildings and marine systems. This architectural design framework transcends intrinsic material limits, establishing a foundational pathway toward intelligent, high-efficiency, and sustainable thermal technologies essential for energy sustainability.

The increasing die size, package dimensions and operating heat flux of AI chips impose stringent requirements on the mechanical compliance and reliability of chip-level thermal interface materials (TIMs). Polymer-based TIMs, particularly silicone gels, offer advantages such as mechanical flexibility, automated dispensability, and warpage accommodation in large packages; however, their application is limited by weak interfacial adhesion and siloxane volatilization. Therefore, it is essential to develop advanced non-silicone thermal gels. This study reports a poly(ionic liquid) (PIL)-based thermally gel TIM. The TIM was fabricated by dispensing a mixture of ionic liquid monomer, Al₂O₃ thermal filler, and initiator, followed by thermal curing, making it compatible with FCBGA dispensing processes (the viscosity before curing was 225 Pa·s). With 70 vol% Al₂O₃ filler, the PIL-based TIM exhibited a low storage modulus of 255 kPa and high interfacial adhesion strengths of 0.95 MPa to Cu and 0.91 MPa to Si. The intrinsic thermal resistance reached 2.4 × 10^-5 m²·K/W, comparable to that of conventional silicone systems. Notably, the interfacial contact thermal resistance with Si (R_c = 1.95 ± 0.87 × 10^-7 m²·K/W) was an order of magnitude lower than that of silicone-based TIMs. Reliability tests showed > 98% coverage after three accelerated aging tests, with no leakage or volatilization. The proof-of-concept study validates the feasibility of PIL-based TIMs and highlights their significant potential for further optimization in next-generation AI thermal management.

The high integration density of modern energy and information devices often results in high power density and intense heat flux. Depending on the operating and optimal temperature range of the device, heat must be either effectively dissipated or retained. Precise regulation of heat flow is essential for the advancement of next-generation energy and information technologies. Dynamic heat flow control and nonlinear thermal transport open new avenues for developing smart battery thermal management systems, solid-state refrigeration devices, and thermal logic elements analogous to electronic circuits. Due to their unique capability to actively modulate heat transfer and exhibit thermal rectification behavior, thermal switches and thermal diodes have shown great potential in managing heat and/or maintaining thermal stability beyond the limits of conventional passive thermal materials and devices. Here, we review recent progress in the design principles, fundamental mechanisms, and applications of thermal switches and thermal diodes for energy and information technologies, and evaluate their potential for practical deployment. Furthermore, we discuss the emerging demands in these sectors and provide future perspectives to inspire applied research toward solving real engineering challenges.

We investigate how metallic rattling modes in Sr₂HgSn simultaneously suppress particle-like (κ_p) and enhance wave-like (κ_c) thermal conductivity via a combined first-principles, force-constant modulation, and Wigner transport analysis. Weak Hg-Sn bonds generate flat phonon bands that relax momentum conservation, intensifying both three- and four-phonon scattering and shortening phonon lifetimes. This dual scattering-coherence mechanism reveals a frequency-selective κ_p - κ_c crossover, leading to a weak temperature-dependent κ_L. Our work establishes rattling as a tunable design strategy for controlling phonon transport in thermoelectrics.

Phonon hydrodynamics is a theoretical framework for predicting nondiffusive heat transport processes in solids at the nanoscale or under high-frequency excitations. This article presents the microscopic and thermodynamic foundations of the theory and reviews its applications. First, we discuss historical and modern derivations of hydrodynamic heat transport equations from the phonon Boltzmann transport equation (BTE), and highlight advanced methods to predict hydrodynamic effects from direct solutions of the BTE beyond the Relaxation Time Approximation. Then, we review the main experiments that uncovered nondiffusive heat transport effects and their interpretation from the hydrodynamic perspective. Overall, the developments summarized in this work establish phonon hydrodynamics as a vital tool for understanding and engineering thermal transport at the nanoscale in data-processing and energy-conversion devices.

The two-temperature model (TTM) has been widely employed in describing ultrafast relaxation dynamics, providing a simple yet powerful framework to study energy relaxation in photoexcited systems. Recently, the time-dependent Boltzmann equation (TDBE) has revealed the limitations of TTM. However, current implementations of the TDBE assume instantaneous electronic thermalization. In this work, we employ first-principles Boltzmann transport simulations to explicitly examine the impact of non-thermal electronic distributions on relaxation processes. By comparing gold, silver, and aluminum as representative cases, we show that while phonons can indeed remain far from equilibrium, the neglect of non-thermal electrons is far more consequential. For gold, the absence of strongly coupled scattering channels makes the influence of non-thermal electrons negligible, rendering the TTM valid. For silver, deviations from the TTM stem mainly from non-thermal electronic effects, and for aluminum, both non-thermal electrons and phonons lead to substantial discrepancies. These findings demonstrate that non-thermalized electrons play a decisive role in out-of-equilibrium ultrafast energy transfer between electrons and phonons, offering a new perspective on the limitations of the TTM.