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.

Icicles are known for their universal conelike shape and rippled surface, and for both these features theories have been developed. However, experimental results appear to be at odds with the existing theories: for pure water in fact very irregular icicles are observed, and it is only if some salt is present that the cone shape and the surface ripples are observed. Here, we investigate the effect of such impurities on the morphology of icicles. We observe surface ripples with a wavelength of approximately equal to $1$ cm that is independent of impurity concentration. Surprisingly, the amplitude of the ripples is zero for ultrapure water and increases rather sharply with impurity concentration. We find that the expulsion of salt from the ice crystal leads to a transition between partial to complete wetting of the water on the icicle, and it is only for the latter case that the icicles become well behaved. This is confirmed by adding a small amount of dye to the water that has different color in the liquid and solid phase, and image the growing icicles. These experiments show that in the presence of impurities in the water (causing complete wetting), the icicles are covered with a thin liquid film that speeds up icicle and ripple growth. In contrast, icicles grown from ultrapure water exhibit partial wetting, and grow due to droplets sliding down in stick-slip motion, leading to an ill-defined overall shape that differs from the theoretically predicted one, and a disappearance of the ripples.

We study the effects of cyclic, athermal quasistatic shear on a model glass-forming system in three dimensions. We utilize the three available orthogonal shear planes, namely $XY,YZ$, and $XZ$ to better explore the energy landscape. Using measurements of the stroboscopic $(\gamma =0)$ energy, we study the effects of using an orthogonal shear direction to perturb unidirectional steady states. We find that each sequence of the unidirectional protocol leads to compaction with the universal, $\mathrm{\Delta }E\sim N^{-1}$ behavior as a function of the number of cycles, $N$. Additionally we find that cyclic shear utilizing multiple shear planes presents hierarchical compaction, producing progressively lower steady-state energies compared to a protocol involving unidirectional cyclic shear alone. Furthermore, with the periodicity of the stroboscopic energy as reference, we show that it is possible to achieve steady-state limit cycles of tunable periodicities using different combinations of the three orthogonal strain directions. We find that such protocols exhibit better annealing as compared to protocols with steady states created using unidirectional shear. We find a nontrivial trend in the annealing energy and the period of the steady-state limit cycle, with an aperiodic protocol appearing to produce the most well-annealed states. Finally, we compare the phase diagram of the average steady-state energy $⟨E_{\mathrm{SS}}⟩$, as a function of the shearing amplitude ${\gamma }_{max}$, using unidirectional and multidirectional protocols, and find that the universal features are preserved.

Developing efficient biatom catalysts for renewable energies is becoming increasingly worthwhile, yet it remains a great challenge. Herein, by means of large-scale first-principles calculations, we report a design principle of coupling main-group metal with transition metal (TM) to explore biatom catalysts for nitric oxide reduction reaction (NORR), namely, $\mathrm{Mg}/\mathrm{Al}/\mathrm{Ga}-\mathrm{TM}$ dimers anchored on nitrogen-doped graphene. We propose a comprehensive screening strategy to recognize promising candidates of such catalysts. Following this strategy, we screen $\mathrm{Mg}-\mathrm{Ni}@\mathrm{NC}$ and $\mathrm{Ga}-\mathrm{Cr}@\mathrm{NC}$ out of 24 candidates as promising biatom catalysts with high activity and selectivity for direct $\mathrm{NO}$-$\mathrm{to}$-${\mathrm{NH}}_3$ conversion. Such high catalytic activity is related to the synergetic interatomic interactions. Moreover, based on the interplay between main-group metal and TM centers, we propose a “donation-backdonation-redonation” mechanism to characterize $\mathrm{NO}$ activation. In addition, $\mathrm{\Delta }{\epsilon }_{s/p\to d}$ is identified as an efficient quantitative descriptor to prereduce the number of such catalyst candidates. Our work opens a strategy for rational design of biatom catalysts toward NORR.

Quantum phase slip (QPS) is the exact dual to the well-known Josephson effect. Although there are numerous proposals for applications of QPS devices, experimental work to develop these remains in the relatively early stages. Significant barriers to exploiting QPS nanowires for useful technologies still exist, such as establishing robust nanowire-fabrication methods that allow coupling to low-loss circuits, and demonstrating control over the QPS process with an experimenter-controlled external bias. Here we report experiments that show that both of these barriers have been overcome. We present measurements at 300 mK of $\mathrm{Nb}\mathrm{N}$ coplanar-waveguide (CPW) resonators embedded with nanowires fabricated using a neon focused ion beam. The internal quality factor exceeds $2\times {10}^4$—significantly higher than previously reported in comparable experiments. The resonator frequency tunes periodically with an applied magnetic field, revealing tunneling of the order parameter that always occurs at half-integer values of the applied flux. In contrast to previous studies of single QPS, the order-parameter tunneling is shown to be adiabatic, demonstrating improved control over energy dissipation in nanowire QPS circuits. Our results highlight a promising pathway towards realizing low-loss nanowire-based QPS devices.

Epitaxial ${\mathrm{La}\mathrm{Fe}\mathrm{O}}_3$ ($\mathrm{LFO}$)-based photocells, of different thicknesses (50–200 nm) have been grown on cubic $\mathrm{LSAT}$ (001) [$({\mathrm{La}\mathrm{Al}\mathrm{O}}_3{)}_{0.3}({\mathrm{Sr}}_2{\mathrm{Ta}\mathrm{Al}\mathrm{O}}_6{)}_{0.7}$] single-crystal substrates, using a ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{Mn}\mathrm{O}}_3$ (LSMO) bottom electrode and different top electrodes [$\mathrm{Pt},{\mathrm{Ba}}_{0.95}{\mathrm{La}}_{0.05}{\mathrm{Sn}\mathrm{O}}_3$ ($\mathrm{BLSO}$)], to determine their photoresponse. The measured short-circuit photocurrent first increases with $\mathrm{LFO}$ thickness and then decreases, and it is larger or smaller, when $\mathrm{Pt}$ or $\mathrm{BLSO}$ electrodes are used, respectively. The corresponding open-circuit voltage displays the opposite trend, being smaller or larger for $\mathrm{Pt}\text{ and }\mathrm{BLSO}$, respectively, which is in excellent agreement with the electronic band alignments determined by x-ray photoelectron spectroscopy and also consistent with the rectifying character of the dark current-voltage data. It turns out that the films display a complex microstructure containing different variants, strained and relaxed, of the orthorhombic ${\mathrm{La}\mathrm{Fe}\mathrm{O}}_3$, that evolves with film thickness and entails the presence of strain gradients and, possibly, flexoelectric fields. We discuss these data and propose that the unavoidable grain boundaries between differently textured ${\mathrm{La}\mathrm{Fe}\mathrm{O}}_3$ crystallites play a significant role on the observed responsivity (2.6 × ${10}^{-4}$ A W${}^{-1}$), found to be larger than in related $\mathrm{LFO}$-based structures.

Cavity magnonics provides a versatile platform to tune the photon-magnon interaction bringing about promising applications for quantum information processing. Here, we implement a metamaterial planar cavity to suppress the radiative damping by engineering the symmetry of the cavity configuration. Then, the mode with suppressed radiative damping, i.e., dark mode, is coupled to the magnon mode in a thin yttrium iron garnet film ($5\mu \mathrm{m}$), which is detected by performing the reflection measurements and spin-pumping experiment. Pronounced anticrossing of the ferromagnetic resonance and the cavity dark mode is observed, where the largest coupling strength reaches 2.5% of the resonant cavity frequency. In addition, the spin wave resonances along the thickness direction are identified, which enhances the spin-pumping signal when they coalesce with the hybridized cavity-magnon-polariton mode. The dark mode excited by the planar metamaterial cavity leads to an improvement in the coherent manipulation of the spin current.

Not so long ago, thermoelectricity in superconductors was believed to be possible only by breaking explicitly the particle-hole (PH) symmetry. Recently, it has been theoretically predicted that a superconducting tunnel junction can develop bipolar thermoelectric phenomena in the presence of a large thermal gradient owing to nonequilibrium spontaneous PH symmetry breaking. The experimental realization of the thermoelectric Josephson engine then followed. Here, we give a more extended discussion and focus on the impact of the Josephson contribution on thermoelectricity modulating the Cooper pairs’ transport in a double-loop superconducting quantum interference device. When the Cooper pairs’ current prevails on the quasiparticle one, the Josephson contribution short circuits the junction thereby screening the thermoelectric effect. We demonstrate that the thermoelectric generation due to the pure quasiparticle transport is phase independent, once Josephson contribution is appropriately removed from the net current measured. At the same time, we investigate an additional metastable state at $V\approx 0$ determined by the presence of the Josephson coupling, which peculiarly modifies the hysteretic behavior of our thermoelectric engine realized. At the end, we also discuss how the current-voltage characteristics are affected by the presence of multiple thermoelectric elements, which improve the generated output power.

Polarized x-ray source is a useful probe for many fields, such as fluorescence imaging, magnetic microscopy, and nuclear physics research. All-optical inverse Compton scattering source (AOCS) based on a laser wakefield accelerator (LWFA) has drawn great attention in recent years due to its compact scale and high performance, especially its potential to generate polarized x rays. Here, polarization-tunable AOCS x rays are generated by a plasma-mirror-based scheme. The linearly and circularly polarized AOCS x rays are measured to have the mean photon energy of $60(\pm 5)/64(\pm 3)$ keV and the single-shot photon yield of approximately $1.1/1.3\times {10}^7$. A Compton polarimeter is designed to diagnose the x-ray polarization states, demonstrating the polarization tunability of AOCS, and indicating that the average polarization degree of the linearly polarized AOCS is $75(\pm 3)\mathrm{\%}$ within 18.2 mrad x-ray divergence.

Streak cameras are one of the most common and convenient devices to measure pulsed emission, e.g., from semiconductor lightsources with picosecond time resolution. However, they are most sensitive in the visible range and possess low or negligible efficiency in the infrared and telecom regime. In this work, we present a frequency conversion based on sum-frequency generation that converts infrared to visible signals while preserving their temporal properties, making them detectable with a streak camera. We demonstrate and verify the functionality of our device by converting the emission from a quantum dot laser.

Cavity spintronics explores light-matter interactions at the interface between spintronic and quantum phenomena. Until now, studies have focused on the hybridization between magnons in ferromagnets and cavity photons. Here, we realize antiferromagnetic cavity magnon polaritons. Hybridization arises from the interaction of the collective spin motion in single hematite crystals (α-${\mathrm{Fe}}_2{\mathrm{O}}_3$) and the microwave field of integrated cavities operating between 18 and 45 GHz. We show theoretically and experimentally that the photon-magnon coupling in the collinear phase is mediated by the dynamic Néel vector and the weak magnetic moment in the canted phase by measuring across the Morin transition. We show that the coupling strength, $\tilde{g}$, scales with the anisotropy field in the collinear phase and with the Dzyaloshinskii-Moriya field in the canted phase. We reach the strong-coupling regime in both canted (cooperativity C > 70 for selected modes at 300 K) and noncollinear phases (C > 4 at 150 K), and thus, towards coherent information-exchange-harnessing antiferromagnetic cavity magnon polaritons. These results provide evidence for a generic strategy to achieve cavity magnon polaritons in antiferromagnets for different symmetries, opening the field of cavity spintronics to antiferromagnetic materials.

For high-intensity laser-solid interactions, the absolute density and surface density gradients of the target at the arrival of the ultrarelativistic laser peak are critical parameters. Accurate modeling of the leading edge-driven target preexpansion is desired to strengthen the predictive power of associated computer simulations. The transition from an initial solid state to a plasma state, i.e., the breakdown of the solid, defines the starting point of the subsequent target preexpansion. In this work, we report on the time-resolved observation of transient laser-induced breakdown (LIB) during the leading edge of high-intensity petawatt-class laser pulses with peak intensities of up to $5.7\times {10}^{21}\mathrm{W}/{\mathrm{cm}}^2$ in interaction with dielectric cryogenic hydrogen jet targets. LIB occurs much earlier than what is typically expected following the concept of barrier suppression ionization. The observation is explained by comparing a characterization study of target-specific LIB thresholds with laser contrast measurements. The results demonstrate the relevance of the laser pulse duration dependence of LIB for high-intensity laser-solid interactions. We provide an effective approach to determine the onset of LIB and thereby the starting point of target preexpansion in other laser-target systems.