Modulating Thermal Conductivity via Targeted Phonon Excitation.

Thermal conductivity is a critical material property in numerous applications, such as those related to thermoelectric devices and heat dissipation. Effectively modulating thermal conductivity has become a great concern in the field of heat conduction. Here, a quantum modulation strategy is proposed to modulate the thermal conductivity/heat flux by exciting targeted phonons.

Chiral Phonons: Prediction, Verification, and Application.

Chirality as an asymmetric property is prevalent in nature. In physics, the chirality of the elementary particles that make up matter has been widely studied and discussed, and nowadays, the concept has developed into the field of phonons. As an important fundamental excitation in condensed matter physics, phonons are traditionally considered to be linearly polarized and nonchiral.

Abnormal Thickness-Dependent Thermal Transport in Suspended 2D PdSe.

Research on 2D materials originally focused on the highly symmetrical materials like graphene, h-BN. Recently, 2D materials with low-symmetry lattice such as PdSe have drawn extensive attention, due to the interesting layer-dependent bandgap, promising mechanical properties and excellent thermoelectric performance, etc. In this work, the phonon thermal transport is studied in PdSe with a pentagonal fold structure.

Low voltage-driven high-performance thermal switching in antiferroelectric PbZrO thin films.

Effective control of heat transfer is vital for energy saving and carbon emission reduction. In contrast to achievements in electrical conduction, active control of heat transfer is much more challenging. Ferroelectrics are promising candidates for thermal switching as a result of their tunable domain structures.

Phonon Chirality Manipulation Mechanism in Transition-Metal Dichalcogenide Interlayer-Sliding Ferroelectrics.

As an ideal platform, both the theoretical prediction and first experimental verification of chiral phonons are based on transition-metal dichalcogenide materials. The manipulation of phonon chirality in these materials will have a profound effect on the study of chiral phonons. In this work, we utilize the sliding ferroelectric effect to realize the phonon chirality manipulation mechanism in transition-metal dichalcogenide materials.

Nonmonotonic dependence of thermal conductivity on surface roughness: A multiparticle Lorentz gas model.

Utilizing surface roughness to manipulate thermal transport has aided important developments in thermoelectrics and heat dissipation in microelectronics. In this paper, through a multiparticle Lorentz gas model, it is found that thermal conductivity oscillates with the increase of surface roughness, and the oscillating thermal conductivity gradually disappears with the increase of nonlinearity. The transmittance analyses reveal that the oscillating thermal conductivity is caused by localized particles due to boundary effects.

Enhancing the ionic conductivity and mechanical properties of PEO-based solid electrolytes through thermal pre-stretching treatment.

Pre-stretching as a method for directing polymer crystallization offers a promising solution for addressing the limitations of solid polymer electrolytes in flexible batteries at ambient temperatures. In this study, we have investigated the ionic conductivity, mechanical behaviour, and microstructural and thermal properties of polyethylene oxide (PEO)-based polymer electrolytes with varying pre-strain levels. The results indicate that thermal stretching-induced pre-deformation can significantly increase the through-plane ionic conductivity, in-plane strength, stiffness of solid electrolytes, and cell-specific capacity.

Ultraflexible two-dimensional Janus heterostructure superlattice: a novel intrinsic wrinkled structure.

The recently reported two-dimensional Janus transition metal dichalcogenide materials present promising applications such as in transistors, photocatalysts, and thermoelectric nanodevices. In this work, using molecular dynamics simulations, the self-assembled in-plane MoSSe/WSSe heterostructure superlattice is predicted with a natural sinusoidal structure constructed by an asymmetric interface. Such a sinusoidal structure shows extraordinary mechanical behavior where the fracture strain can be enhanced up to 4.

Chiral-phonon-activated spin Seebeck effect.

Utilization of the interaction between spin and heat currents is the central focus of the field of spin caloritronics. Chiral phonons possessing angular momentum arising from the broken symmetry of a non-magnetic material create the potential for generating spin currents at room temperature in response to a thermal gradient, precluding the need for a ferromagnetic contact. Here we show the observation of spin currents generated by chiral phonons in a two-dimensional layered hybrid organic-inorganic perovskite implanted with chiral cations when subjected to a thermal gradient.

Reducing interfacial thermal resistance by interlayer.

Heat dissipation is crucial important for the performance and lifetime for highly integrated electronics, Li-ion battery-based devices and so on, which lies in the decrease of interfacial thermal resistance (ITR). To achieve this goal, introducing interlayer is the most widely used strategy in industry, which has attracted tremendous attention from researchers. In this review, we focus on bonding effect and bridging effect to illustrate how introduced interlayer decreases ITR.

Regulating the thermal conductivity of monolayer MnPS by a magnetic phase transition.

In this study, based on calculations and the phonon Boltzmann transport equation, we found that magnetic phase transitions can lead to a significant change in the thermal conductivity of monolayer MnPS. Around the Néel temperature (78 K) with the antiferromagnetic-paramagnetic (AFM-PM) phase transition, its thermal conductivity increases from 14.89 W mK (AFM phase) to 103.

Chiral Phonon Diode Effect in Chiral Crystals.

The diode effect means that carriers can only flow in one direction but not the other. While diode effects for electron charge, spin, or photon have been widely discussed, it remains a question whether a chiral phonon diode can be realized, which utilizes the chiral degree of freedom of lattice vibrations. In this work, we reveal an intrinsic connection between the chiralities of a crystal structure and its phonon excitations, which naturally leads to the chiral phonon diode effect in chiral crystals.

Interface thermal resistance induced by geometric shape mismatch: A multiparticle Lorentz gas model.

Poor heat dissipation caused by interface thermal resistance (ITR, or Kapitza resistance) has long been the bottleneck that limits the further miniaturization of integrated circuit. In this paper, different from previous studies on ITR induced by conjunction of two different materials, the ITR of a homogeneous stepped system is studied through the multiparticle Lorentz gas model. It is found that ITR can be triggered by pure geometric shape mismatch, and decreases when the degree of mismatch decreases.

Chiral Phonons and Giant Magneto-Optical Effect in CrBr 2D Magnet.

Phonons with chirality determine the optical helicity of inelastic light scattering processes due to their nonzero angular momentum. Here it is shown that 2D magnetic CrBr hosts chiral phonons at the Brillouin-zone center. These chiral phonons are linear combinations of the doubly-degenerate E phonons, and the phonon eigenmodes exhibit clockwise and counterclockwise rotational vibrations corresponding to angular momenta of l = ± 1.

Modification of thermal transport in few-layer MoS by atomic-level defect engineering.

Molybdenum disulfide (MoS2) has attracted significant attention due to its good charge carrier mobility, high on/off ratio in field-effect transistors and novel layer-dependent band structure, with potential applications in modern electronic, photovoltaic and valleytronic devices. Despite these advantages, its thermal transport property has often been neglected until recently. In this work, we probe phonon transport in few-layer MoS2 flakes with various point defect concentrations enabled by helium ion (He+) irradiation.

Gate-tunable chiral phonons in low-buckled group-IVA monolayers.

We investigate the electric response of chiral phonons on the low-buckled group-IVA monolayers by performing first-principles calculations. The vertical electric field breaks the degeneracy of phonon modes at high-symmetry ±points of the phonon Brillouin zone, and the size of the phononic gap is proportional to the strength of the electric field. The gapped phonon modes at ±possess chiralities with considerable phonon circular polarizations and discrete phonon pseudoangular momenta.

Anomalous hybridization complementation effect on phonon transport in heterogeneous nanowire cross junction.

Controlling phonon transport via its wave nature in nanostructures can achieve unique properties for various applications. In this paper, thermal conductivity of heterogeneous nano cross junction (hetero-NCJ) is studied through molecular dynamics simulation. It is found that decreasing or increasing the atomic mass of four side wires (SWs) severed as resonators, thermal conductivity of hetero-NCJ is enhanced, which is larger than that of homogeneous NCJ (homo-NCJ).

Propagating Chiral Phonons in Three-Dimensional Materials.

Chiral phonons were initially proposed and experimentally verified in two-dimensional (2D) systems. Their intriguing effects have generated profound impacts on multiple research fields. However, all chiral phonons reported to date are constrained to be local, in the sense that their group velocities vanish identically.

Strain-driven dynamic stability and anomalous enhancement of thermal conductivity in graphene-like IIA-VI monolayer monoxides.

Graphene-like IIA-VI monolayer monoxides have been predicted to be novel two-dimensional materials with intrinsic bandgap, which makes them promising prospect for electronics and optoelectronics applications. In the field of microelectronics, heat dissipation is considered as the bottleneck that limits further development. Thus, the effective regulation in thermal transport is of great interest for designing novel devices.

Enhancement of interface thermal conductance between Cr-Ni alloy and dielectric via Cu nano-interlayer.

Facilitating interfacial thermal transport is highly desirable for various engineering applications, such as improving heat dissipation in microelectronics and efficiency of electrothermal heating element. Here, the interface thermal conductances (ITCs) of CrNi/MgO and CrNi/AlOinterfaces are studied through the non-equilibrium molecular dynamics simulation. It is found that the two ITCs can be hugely enhanced by 3 and 2.

Customizing the reduction of individual graphene oxide flakes for precise work function tuning with meV precision.

Being able to precisely control the reduction of two-dimensional graphene oxide films will open exciting opportunities for tailor-making the functionality of nanodevices with on-demand properties. Here we report the meticulously controlled reduction of individual graphene oxide flakes ranging from single to seven layers through controlled laser irradiation. It is found that the reduction can be customized in such a precise way that the film thickness can be accurately thinned with sub-nanometer resolution, facilitated by extraordinary temperature gradients >10 K nm across the interlayers of graphene oxide films.

Electronic and thermal properties of monolayer beryllium oxide from first principles.

Monolayer beryllium oxide (BeO), a new graphene-like metal oxide material, has attracted tremendous interest since it was demonstrated to have high dynamic, thermal, kinetic and mechanical stabilities in recent years. This discovery enriches the catalogue of 2D materials and paves the way for the exploration of relevant properties. In this work, the electronic and thermal properties of monolayer BeO are predicted by first-principles calculations.

Thermal Hall effect from a modified Lorentz gas model.

We systematically investigate the thermal Hall effect in a Lorentz gas model with rotating circular scatterers; the rotating scatterers play a role similar to the magnetic field. The modified Lorentz gas model is a normal thermal transport system that satisfies Fourier law: the thermal conductivity is independent of the model length. We find that the intensity of the Hall effect changes its sign when the rotating direction of disks changes and it is independent of the magnitude of longitudinal temperature difference and only dependent of the average longitudinal temperature: it decreases with increasing the average temperature, especially at low angular velocity.

Optimized interfacial thermal coupling between two nonlinear systems.

Interfacial thermal resistance (ITR, or Kapitza resistance) is the bottleneck that limits the further growth of density for integrated circuit. In this paper, we study the interfacial thermal coupling between two nonlinear systems by using a one-dimensional FPU-β heterojunction model through molecular dynamics simulation. It is found that the ITR first decreases rapidly and then increases slowly with the increase of interface coupling coefficient (ICC).