A quantitative understanding of the microscopic mechanisms responsible for damping in van der Waals nanomechanical resonators remains elusive. In this work, we investigate van der Waals magnets, where the thermal expansion coefficient exhibits an anomaly at the magnetic phase transition due to magnetoelastic coupling. Thermal expansion mediates the coupling between mechanical strain and heat flow and determines the strength of thermoelastic damping (TED). Consequently, variations in the thermal expansion coefficient are reflected directly in TED, motivating our focus on this mechanism. We extend existing TED models to incorporate anisotropic thermal conduction, a critical property of van der Waals materials. By combining the thermodynamic properties of the resonator material with the anisotropic TED model, we examine dissipation as a function of temperature. Our findings reveal a pronounced impact of the phase transition on dissipation, along with transitions between distinct dissipation regimes controlled by geometry and the relative contributions of in-plane and out-of-plane thermal conductivity. These regimes are characterized by the resonant interplay between strain and in-plane or through-plane heat propagation. To validate our theory, we compare it to experimental data of the temperature-dependent mechanical resonances of FePS3 resonators.

We theoretically investigate the enhancement of the charging power in a Dicke quantum battery which consists of an array of N two-level systems (TLS)coupled to a single mode of cavity photons. In the limit of small N, we analytically solve the time evolution for the full charging process. The eigenvectors of the driving Hamiltonian are found to be pseudo-Hermite polynomials and the evolution is thus interpreted as harmonic oscillator like behaviour. Then we demonstrate the average charging power using a collective protocol is (Formula presented.) times larger than that of the parallel protocol when transferring the same amount of energy. Unlike previous studies, we point out that such quantum advantage does not originate from entanglement but is due to the coherent cooperative interactions among the TLSs. Our results provide intuitive quantitative insight into the dynamic charging process of a Dicke battery and can be observed under realistic experimental conditions.

We theoretically investigate the collective excitations of multiple (sub)millimeter-sized ferromagnets mediated by waveguide photons. By the position of the magnets in the waveguide, the magnon-photon coupling can be tuned to be chiral, i.e., magnons only couple with photons propagating in one direction, leading to an asymmetric transfer of angular momentum and energy between the magnets. A large enhancement of the magnon number population can be achieved at an edge of a long chain of magnets. The chain also supports standing waves with low radiation efficiency that are inert to the chirality.

We propose a method to control surface phonon transport by weak magnetic fields based on the pumping of surface acoustic waves (SAWs) by magnetostriction. We predict that the magnetization dynamics of a nanowire on top of a dielectric films injects SAWs with opposite angular momenta into opposite directions. Two parallel nanowires form a phononic cavity that at magnetic resonances pump a unidirectional SAW current into half of the substrate.

We report strong chiral coupling between magnons and photons in microwave waveguides that contain chains of small magnets on special lines. Large magnon accumulations at one edge of the chain emerge when exciting the magnets by a phased antenna array. This mechanism holds the promise of new functionalities in nonlinear and quantum magnonics.

The dissipative light-matter coupling can cause the attraction of two energy levels, i.e., level attraction, when competing with the coherent coupling that induces usual Rabi-level splitting. The level attraction shows attractive potential for topological information processing. However, the underlying microscopic quantum mechanism of dissipative coupling still remains unclear although the behavior has been understood to root in the non-Hermitian physics, which brings difficulties in quantifying and manipulating the competition between coherence and dissipation and thereby the flexible control of level attraction. Here, by coupling a magnon mode to a cavity supporting both standing and traveling waves, we identify the traveling-wave state to be responsible for magnon-photon dissipative coupling. By characterizing the radiative broadening of a magnon linewidth, we quantify the coherent and dissipative coupling strengths and their competition. The effective magnon-photon coupling strength, as a net result of competition, is analytically presented using quantum theory to show good agreement with measurements. In this manner, we extend the control dimension of level attraction by tuning field torque on magnetization or global cavity geometry. Our findings provide insights on engineered coupled harmonic oscillator systems.

As a powder-bed-based additive manufacturing technology, selective laser melting (SLM) offers high-level flexibility and enables efficient fabrication of complex parts. In connection with complex thermal events occurring during dynamic sequential layer-by-layer deposition, the as-built material is usually hierarchical at different length scales and possesses anisotropy at each level. As a result of a moderate heating temperature of the baseplate and high cooling rates involved in the process, the as-built Ti-6Al-4V alloy has an α′ martensite microstructure. Microstructure evolution occurring during post-SLM heat treatment is strongly affected by the stability of the initial acicular martensite. The present study was aimed at developing an optimum post-SLM heat treatment scheme at a temperature below the β transus temperature, based on the understanding of microstructure evolution occurring during subtransus treatment and the resultant mechanical properties of the alloy. It was observed that the growth of the α and β phases during the heat treatment was inhibited by the initial α′ phase. A higher heating temperature could effectively improve microstructure homogeneity on a micrometer-scale to some extent. Heating temperature affected the strength and fracture strain of the alloy far more than cooling rate. A post-SLM heat treatment at a temperature of 850 °C or higher could lead to an improvement of fracture strain to the level of the forged counterpart, accompanied by the losses in yield strength and ultimate compressive strength from the as-built values. Full annealing (i.e., subtransus treatment at a high temperature) was thus recommended to be an appropriate post-SLM heat treatment for Ti-6Al-4V.