We theoretically clarify the mechanism of the strain-tuning effect for control of the mechanical nonlinearity in doubly clamped MEMS beam resonators and experimentally demonstrate that nonlinearity can be effectively suppressed with a preloaded lattice-mismatch strain in the MEMS beam. Mechanical nonlinearity arises from the hardening- and softening-nonlinearity terms in the Duffing motion equation of the MEMS beam. By approaching the buckling condition of the MEMS beam, the substantially increased softening nonlinearity greatly compensates for the hardening nonlinearity, resulting in suppression of the total nonlinearity. Utilizing this knowledge, we fabricate ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ MEMS beams with a preloaded lattice-mismatch strain, which is achieved by adding a small amount (x = ∼0.4%) of indium to the $\mathrm{Ga}\mathrm{As}$ MEMS beam during wafer growth. The buckling condition in the experiment is achieved by carefully modulating the length of the ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ MEMS beams. As a result, mechanical nonlinearity is largely modulated from hardening to softening and reaches a quasizero value near the buckling condition, demonstrating the effectiveness of using lattice mismatch for controlling the mechanical nonlinearity of MEMS resonators.

Two-dimensional α-${\mathrm{In}}_2{\mathrm{Se}}_3$ has drawn broad attention due to its high photoresponse and unique room-temperature interlocked in-plane and out-of-plane ferroelectricity with an ultralow switching electric field. Here, we investigate the photoresponse in a lateral monolayer (ML) α-${\mathrm{In}}_2{\mathrm{Se}}_3$ p-i-n junction by using ab initio quantum transport simulations. The maximum photoresponses of the lateral α-${\mathrm{In}}_2{\mathrm{Se}}_3$ p-i-n junction are up to 69.2 and 31.6 mA/W for the ferroelectric wurtzite and zincblende phases (shortly named WZ’ and ZB’) α-${\mathrm{In}}_2{\mathrm{Se}}_3$, respectively, which are 8–17 times higher than that of the extensively researched graphene photodetector (4 mA/W). Remarkably, the ferroelectric photoresponses, defined as the photoresponse change ratio between the two ferroelectric states, of the lateral ML WZ’ and ZB’-${\mathrm{In}}_2{\mathrm{Se}}_3$ photodetectors have average values of 127% and 121% with surprising maximum values of $2\times {10}^6\mathrm{\%}$ and $1\times {10}^7\mathrm{\%}$, respectively. The physical mechanism comes from the electron density redistribution altered by the atomic displacements due to the polarization switch, rather than the built-in potential change induced by the surface polarization charges. Such ferroelectric-tunable photoresponses in the α-${\mathrm{In}}_2{\mathrm{Se}}_3$ photodetector suggest a potential in the fabrication of future optical detection and storage integrated devices.

Square-root topology offers a distinctive scheme towards topological phases with unconventional spectral properties. In many cases, the formation of square-root topology is governed by the inherent lattice symmetry, with honeycomb lattices being prominent examples. Here, we report on the experimental discovery of square-root higher-order topological insulator phases in an acoustic metamaterial with decorated rectangular lattice. Through acoustic pump-probe techniques, we explore the boundary-dependent topological edge and corner states in both the parent and square-root acoustic metamaterials. We further validate their higher-order topologies as well as their spectral connections via various simulations. Our work not only substantiates the square-root higher-order topology in rectangular-lattice systems from the experimental aspect, but also serves as a step towards versatile higher-order topological phenomena in photonic, acoustic, and mechanical metamaterials.

As a powerful optical tool, spectrometers are widely used in materials analysis and light-source characterization. Although commercial spectrometers based on dispersive diffraction or Fourier transform offer high resolution and broad dynamic range, spatial information of the sample is lost, limiting its application in snapshot hyperspectral imaging. Herein, we propose a computational spectrometer based on the tailored point spread function of the imaging system that uses disordered microstructures fabricated by low-cost photolithography. The spectrometer achieves a high quantum efficiency ($Q_{\mathrm{avg}}\sim 60\mathrm{\%}$) and ultracompact footprint as low as $24.5\times 24.5\mu {\mathrm{m}}^2$, exhibits outstanding performance in weak-light hyperspectral imaging (e.g., Raman or fluorescence spectroscopy) in the microscopic system. Apart from the advancements mentioned above, our spectrometer offers good compatibility with commercial microscopes, implying it is a promising candidate for spectral imaging in chemistry, biology, and others.

Comagnetometers have been widely used in fundamental research, such as tests of spin-gravity coupling and searches for permanent electric dipole moments (EDMs). Here, we report a comagnetometer that consists of simultaneous closed-loop oscillation of the $F=1$ and $F=2$ hyperfine Zeeman transitions of optically aligned ${}^{87}$$\mathrm{Rb}$ atoms. The Allan deviation of the $F=2$ and $F=1$ oscillation-frequency ratio reaches $1\times {10}^{-9}$ after running continuously for 2 days, corresponding to a sensitivity of approximately $4\times {10}^{-19}\mathrm{eV}$ for the measurement of the hypothetical spin-dependent gravitational energy of the proton. The long-term stability of the comagnetometer can be further improved by system-level thermal control and optimization of the experimental parameters.

We study the magnetic and electrical transport properties of magnetic tunnel junctions (MTJs) consisting of a ${\mathrm{Co}}_{75}{\mathrm{Mn}}_{25}{/\mathrm{Mo}/\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ multilayer prepared using a mass-production-compatible magnetron sputtering system. The ${\mathrm{Co}}_{75}{\mathrm{Mn}}_{25}{/\mathrm{Mo}/\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ multilayer sandwiched between two MgO layers exhibits remarkable perpendicular magnetic anisotropy, and a uniaxial magnetic anisotropy constant as large as $0.2{\mathrm{MJ}/\mathrm{m}}^3$ is achieved by optimizing the ${\mathrm{Co}}_{75}{\mathrm{Mn}}_{25}$ layer thickness as well as the annealing temperature. The current-in-plane tunneling measurement reveals a large tunneling magnetoresistance of over 100% in perpendicularly magnetized MTJs. These experimental results indicate the applicability of ${\mathrm{Co}}_{75}{\mathrm{Mn}}_{25}$ alloy for magnetic random access memory devices.

Near-field radiative heat transfer between closely placed objects may exceed the far-field black-body radiation limit by orders of magnitude, especially between polaritonic materials. Great efforts have been made to experimentally measure this fundamental effect in various systems. In this work, we manage to experimentally characterize the near-field thermal emission between less explored plasmon-phonon hybrid material systems made of a graphene-$\mathrm{Si}\mathrm{C}$ heterostructure. The experiment is carried out using a custom-designed all-optical measurement setup. A heat flux enhancement factor of 26 over the black-body radiation limit is obtained at a 150-nm vacuum gap. Three fundamental modes, i.e., surface plasmon and phonon polaritons with frustrated modes, are identified to contribute the near-field heat flux in this hybrid system. The measured results are well reproduced from the analytical calculations, indicating the robustness of the measurement. Deeper experimental explorations for near-field heat transfer between more complicated material systems could be encouraged in the future.

Band-stop filters play an important role in wireless communications by blocking signals within specified frequency bands and allowing useful frequencies to pass through. As a special type of higher symmetry, glide symmetry achieves the reconfiguration of band gaps by manipulating the dispersion relationships of periodic structures, which is of great value for filter designs. However, existing band-stop filters based on glide symmetry are mainly realized with three-dimensional transmission lines, and only one band gap is reconfigured. Here, we explore glide symmetry in planar substrate-integrated coaxial lines (SICL) to reconfigure multiple band gaps and, in the meantime, customize their bandwidths and locations. For practical applications, three types of SICL band-stop filters with different glide symmetries are designed, fabricated, and measured. By changing the geometry of the glide-symmetric inner conductor, two distinct stopbands can be reconfigured and their bandwidths can be customized. The measurement results agree well with the numerical results, demonstrating high controllability and good filtering performance. The proposed glide-symmetric SICL provides a facile method to implement controllable band-stop filters and may facilitate more planar implementations with glide symmetry for dispersion manipulations.

Pumping at low Reynolds number is a ubiquitously encountered feature, both in biological organisms and engineered devices. Generating net flow requires the presence of an asymmetry in the system, which traditionally comes from geometric flow rectifiers. Here, we study a valveless system of $N$ oscillating pumps in series, where the asymmetry comes not from the geometry but from time, that is, the phase shifts between the pumps. Experimental and theoretical results are in very good agreement. We provide the optimal phase shifts leading to the maximal net flow in the continuous $N\to \mathrm{\infty }$ limit. The maximal flow rate is larger by 25% than that of a traditional peristaltic sinusoidal wave, for the same amplitude of actuation. Our results hopefully pave the way for the design of more efficient microfluidic pumps.

A finite-temperature micromagnetic study of magnetization switching and write-error rates in a perpendicular magnetic tunnel junction with and without synthetic antiferromagnetic layer (SAF) is presented. In the absence of SAF, magnetization switching is induced by domain-wall nucleation and propagation. Although the various modes of domain-wall propagation are observed to delay switching, it does not show an appreciable impact on the overall write-error-rate slopes. In the presence of the nonuniform stray field from the SAF assembly, the domain-wall-based switching modes turn on more complex magnetization dynamics that impedes the switching process. In cases where the SAF layers fail to balance each other contributing to a stronger stray field, incoherent switching modes give rise to metastable states with significantly longer lifetimes, and a dramatic change in the write-error slopes is observed. Simulation results are compared to recent experimental findings from time-domain measurements of spin-transfer-torque switching and measurements of anomalous write-error rates. These results directly prove the long-predicted relation of the SAF stray field to write-error anomaly in perpendicular spin-transfer-torque magnetic random-access memory and could be useful to solve the anomalous write-error problems.

Bilayer graphene is a nanomaterial that allows for well-defined, separated quantum states to be defined by electrostatic gating and, therefore, provides an attractive platform to construct tunable quantum dots. When a magnetic field perpendicular to the graphene layers is applied, the graphene valley degeneracy is lifted, and splitting of the energy levels of the dot is observed. Although bilayer graphene quantum dots have recently been realized in experiments, it is critically important to devise robust methods that can identify the observed quantum states from accessible measurement data. Here, we develop an efficient algorithm for extracting the model parameters needed to characterize the states of a bilayer graphene quantum dot. Specifically, we put forward a Hamiltonian-guided random search method and demonstrate robust identification of quantum states on both simulated and experimental data.

Quantum error correction will be an essential ingredient in realizing fault-tolerant quantum computing. However, most correction schemes rely on the assumption that errors are sufficiently uncorrelated in space and time. In superconducting qubits, this assumption is drastically violated in the presence of ionizing radiation, which creates bursts of high-energy phonons in the substrate. These phonons can break Cooper pairs in the superconductor and, thus, create quasiparticles over large areas, consequently reducing qubit coherence across the quantum device in a correlated fashion. A potential mitigation technique is to place large volumes of normal or superconducting metal on the device, capable of reducing the phonon energy to below the superconducting gap of the qubits. To investigate the effectiveness of this method, we fabricate a quantum device with four nominally identical nanowire-based transmon qubits. On the device, half of the niobium-titanium-nitride ground plane is replaced with aluminum ($\mathrm{Al}$), which has a significantly lower superconducting gap. We deterministically inject high-energy phonons into the substrate by voltage biasing a galvanically isolated Josephson junction. In the presence of the small-gap material, we find a factor of 2–5 less degradation in the injection-dependent qubit lifetimes and observe that the undesired excited qubit state population is mitigated by a similar factor. We furthermore turn the $\mathrm{Al}$ normal with a magnetic field, finding no change in the phonon protection. This suggests that the efficacy of the protection in our device is not limited by the size of the superconducting gap in the $\mathrm{Al}$ ground plane. Our results provide a promising foundation for protecting superconducting-qubit processors against correlated errors from ionizing radiation.

Dielectric loss is one of the major decoherence sources of superconducting qubits. Contemporary high-coherence superconducting qubits are formed by material systems mostly consisting of superconducting films on substrate with low dielectric loss, where the loss mainly originates from the surfaces and interfaces. Among the multiple candidates for material systems, a combination of titanium nitride ($\mathrm{Ti}\mathrm{N}$) film and sapphire substrate has good potential because of its chemical stability against oxidization and its high quality at interfaces. In this work, we report a $\mathrm{Ti}\mathrm{N}$ film deposited onto sapphire substrate achieving low dielectric loss at the material interface. Through the systematic characterizations of a series of transmon qubits fabricated with identical batches of $\mathrm{Ti}\mathrm{N}$ base layers but different geometries of qubit shunting capacitors with various participation ratios of the material interface, we quantitatively extract the loss-tangent value at the substrate-metal interface, which is smaller than $8.9\times {10}^{-4}$ in a 1-nm disordered layer, and a limiting quality factor of about 7.3 million. By optimizing the interface participation ratio of the two-dimensional (2D) transmon qubit, we reproducibly achieve a quality factor of 5.7 million on average. The best 2D qubits show lifetimes of up to $300\mu \mathrm{s}$ and quality factors achieving 8.1 million. We demonstrate that $\mathrm{Ti}\mathrm{N}$ film on sapphire substrate is an ideal material system for high-coherence superconducting qubits. Our analyses further suggest that the interface dielectric loss around the Josephson-junction part of the circuit could be the dominant limitation of lifetimes for state-of-the-art transmon qubits.

Coherent manipulation of atomic states is highly desirable in numerous applications spanning from fundamental physics to metrology. In this study, we propose and demonstrate, theoretically and experimentally, the simultaneous observation in a vapor cell of dark and bright resonances that provide, through a differential-detection stage, an output coherent-population-trapping atomic resonance that benefits from a doubled amplitude and high common-mode noise rejection. This advanced spectroscopic scheme might be of interest for the development of high-performance vapor-cell atomic clocks, sensors, or high-resolution spectroscopy experiments.

Whether the electroluminescence turn-on of quantum-dot light-emitting diodes (QLEDs) is determined by electrons or holes has long been controversial. Given that the charge-carrier trapping or/and capturing processes affect the current measured through an organic semiconductor film, then the long-lived trap information can be extracted by measuring the current through the film with a periodic stepwise-increasing voltage. We develop easy-to-operate technology to detect the long-lifetime traps in the organic small-molecule materials and demonstrate that the turn-on behavior of the QLEDs is determined by the hole injection. Moreover, it is verified that the long-lived hole traps are also responsible for the luminance overshoot behavior for the device driven by a constant current. We believe this characterization technology can provide a significant platform to deeply understand the properties of both materials and photoelectronic devices.

Metamaterials facilitate on-demand manipulations of mass diffusion and have been broadly employed in many fields covering optics, electronics, and particle dynamics. However, the applications of existing mass-diffusion metamaterials are severely limited due to the lack of intelligence when it comes to dynamic environments. To solve the problem, we bestow intelligence on metashells by utilizing transformation-invariant metamaterials, thus proposing intelligent chameleonlike metashells for mass diffusion. Such metashells not only automatically change their efficient parameters to adapt to environmental change but also cost no energy. Based on it, we further design an irregular-shaped chameleonlike concentrator and circular chameleonlike rotator. Meanwhile, we offer experimental suggestions combined with layered structure devices to validate our proposal as well. Our study may be an inspiration for intelligentializing mass-diffusion metamaterials in electronics and plasma physics.

Time-dependent dielectric breakdown (TDDB) is a crucial issue for the dielectric reliability. In this work, we present a full three-dimensional mechanistic model for calculation of the TDDB process in polycrystalline thin films. The model is based on the multiphonon trap-assisted tunneling theory and takes into account the intrinsic three-dimensional discreteness of traps at the dielectric grain boundaries. The leakage current density is calculated by solving coupled three-dimensional master equation and Poisson equation. The net phonon emission associated with each charge trapping and release event is treated as a local point heat source, which then enters the Fourier heat equation for three-dimensional temperature distribution calculation. The generated trap is determined by local temperature and electric field, which is subsequently included in the next round of calculation of electric and thermal properties. A positive feedback loop gradually leads to an increase of trap density, temperature, and leakage current density, and finally the dielectric breakdown. Our model can, to a good approximation, reproduce the experimental leakage current density-voltage characteristics and the Weibull distribution of time to breakdown at different dielectric thicknesses, stress voltages, and environmental temperatures. We find that in realistic devices, the three-dimensional trap-to-trap transport of electrons contributes a non-negligible part to the leakage current when the dielectric approaches breakdown. Our approach of three-dimensional mechanistic simulation is computationally efficient such that evolution of ${10}^3$ traps during the TDDB process can be easily performed on a standard desktop computer.

Recently, the nanoscale quantum heat engine (QHE) has become one of the most productive areas of research, due to its role as a conduit for excess heat. Regarding the low thermal conductance and suitable structural properties of transition-metal dichalcogenides (TMDs), here, we design a highly efficient spin and valley QHE in a normal-ferromagnetic-normal TMD-based tunnel junction. Spin splitting caused by the exchange field and the huge spin-orbit coupling (SOC) of TMDs leads to a remarkable spin-valley–dependent Seebeck coefficient with a sharp peak at $E\approx E_F$. Application of the gate voltage changes the bands from conduction to valence; thus, a remarkable spin-valley–dependent Seebeck and conductance are observed, leading to a large gate- and exchange-field-tunable spin- and valley-dependent maximum power, which is greatly enhanced compared to other two-dimensional materials such as silicene- and graphene-based QHEs. Additionally, a enormous gate-controllable figure of merit and, consequently, a high efficiency at maximum power are achieved in this device, which confirms the advantage of using TMD-based junctions for highly efficient QHEs. These findings may open the door to the design of spin-valley caloritronics devices based on TMDs.

While several experiments claim that two-level system (TLS) defects in amorphous surfaces and interfaces are responsible for energy relaxation in superconducting resonators and qubits, none can provide quantitative explanation of their data in terms of the conventional noninteracting TLS model. Here a model that interpolates between the interacting and noninteracting TLS loss tangent is proposed to perform numerical analysis of experimental data and extract information about TLS parameters and their distribution. As a proof of principle, the model is applied to TESLA cavities that contain only a single lossy material in their interior, the niobium-niobium oxide interface. The best fits show interacting TLSs with a sharp modulus of electric dipole moment for both thin ($5\mathrm{nm}$) and thick ($100\mathrm{nm}$) oxides, indicating that the TLSs are “atomic” instead of “glassy.” The proposed method can be applied to other devices with multiple material interfaces and substrates, with the goal of elucidating the nature of TLSs causing energy loss in resonators and qubits.