Investigation of transport properties is fundamental for characterizing electronic properties and phase transitions. However, most of the transport measurements on conductive layers have been performed at macroscopic scales, and thus the development of microscopic methods to measure transport is pivotal. Scanning tunneling potentiometry (STP) is a powerful tool for investigating surface conductivity at nanoscale spatial resolutions. However, it is still challenging to conduct STP studies at low temperatures and most of the low-temperature studies were performed on samples that were prepared ex situ. In this study, we developed a low-temperature STP and demonstrated its performance on monoatomic metal films formed on $\mathrm{Si}(111)$ substrates that were prepared in situ. Stable operation at low temperatures enables us to extract the electrochemical potential originating from the surface transport by canceling out the potential due to thermal differences and artifacts arising from the nonlinearity of the density of states (DOS). We also formulated the nonlinear-DOS artifact and confirmed it by comparing with the nonlinearity obtained by scanning tunneling spectroscopy.

We present a frequency-tunable magnetoacoustic oscillator (MAO) that operates in two distinct dynamical regimes. Its core magnetoacoustic resonator comprises a yttrium-iron-garnet (YIG) layer epitaxially grown on a gadolinium-gallium-garnet (GGG) substrate. By optimizing the YIG thickness, we achieve a strong magnetoelastic coupling (approximately 1 MHz) between the YIG ferromagnetic resonance (FMR) and high-overtone bulk acoustic resonances (HBARs) in the 1–2 GHz range. This high coupling strength eliminates the need for bulky components—such as preselectors and circulators—while preserving the ability to lock onto specific acoustic modes. By adjusting the loop overamplification, the MAO can be locked exclusively to the high-quality-factor magnetoacoustic HBARs (low-phase-noise regime) or to both HBARs and the FMR mode (complex regime). In the low-phase-noise regime, the oscillator operates only at specific values of the applied magnetic field and exhibits discrete frequency tuning steps of 3.281 MHz, corresponding to the separation between neighboring HBAR modes. In the complex regime, the involvement of the FMR mode enables continuous frequency tuning, though with phase-noise characteristics that vary depending on the applied-field values. Moreover, in the low-phase-noise regime, the MAO’s phase noise is reduced by 30 dB relative to operation purely on the YIG FMR mode, which agrees with the measured FMR and HBAR $Q$ factors.

As a material platform for spintronics, ferrimagnets have garnered considerable attention because of their unique behavior. Recently, interlayer Dzyaloshinskii-Moriya interaction (DMI) has significantly heightened interest in its ability to design three-dimensional long-range chiral spin textures, thereby promising enhancements in the performance of magnetic random-access memory devices. To date, experimental reports primarily focused on the observation of interlayer DMI and its field-free switching capability, while systematic investigations into the temperature dependence of interlayer DMI in ferrimagnetic systems are lacking. Here, we experimentally observe a record-high interlayer DMI effective field and demonstrate the strongly temperature-dependent interlayer DMI strength within a trilayer system incorporating the ferrimagnet TbFe. Our results show that temperature can significantly manipulate the strength of interlayer DMI in trilayer structures composed of a ferrimagnetic rare-earth and transition-metal alloy, consistent with first-principles calculations. These insights herald an effective methodology to modulate the strength of interlayer DMI, offering significant advantages for the prospective development of semiconductor devices based on interlayer DMI.

We report on a stable form of pulsed electroluminescence in a dopant-free direct band gap semiconductor heterostructure that we coin the “tidal effect.” Swapping of an inducing gate voltage in an ambipolar field effect transistor allows incoming and outgoing carriers of opposite charge to meet and recombine radiatively. We develop a model to explain the carrier dynamics that underpins the frequency response of the pulsed electroluminescence intensity. Higher mobilities enable larger active emission areas than in previous reports, as well as stable emission over long timescales.

It has been experimentally established that $\mathrm{Bi}$ doping drastically enhances the nonradiative recombination in MA$\mathrm{Pb}\mathrm{Br}$${}_3$ (where MA represents the methylammonium ion), but the microscopic mechanism underlying this experimental observation remains unclear. Here, we perform rigorous first-principles calculations to investigate the nonradiative recombination in MA$\mathrm{Pb}\mathrm{Br}$${}_3$ with $\mathrm{Bi}$ doping. We show that while $\mathrm{Bi}$${}_{\mathrm{Pb}}$ substitutional defects themselves are not a nonradiative recombination center, $\mathrm{Bi}$ doping significantly alters the Fermi level, leading to significantly reduced formation energy of bromine interstitials ($\mathrm{Br}$${}_i$). Bromine interstitials are, in fact, a strong nonradiative recombination center with a calculated total capture coefficient of ${10}^{-7}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at room temperature, agreeing well with experiment. Hence, $\mathrm{Bi}$${}_{\mathrm{Pb}}$ could indirectly enhance the nonradiative recombination in MA$\mathrm{Pb}\mathrm{Br}$${}_3$ by promoting the formation of efficiency-killing $\mathrm{Br}$${}_i$. These findings underscore a detrimental effect of heterovalent cation doping, which may inadvertently introduce nonradiative recombination centers and limit the performance of perovskite optoelectronic devices.

Hyperbolic surface plasmon polaritons (SPPs), which can be achieved in artificially structured metasurfaces, are garnering significant attention due to their directional propagation and their ability to support an extremely high density of states. In this study, we demonstrate that monolayer ${\mathrm{Zr}\mathrm{Te}}_5$ can serve as a natural two-dimensional (2D) hyperbolic material capable of supporting hyperbolic SPPs. The hyperbolic region is situated in the infrared regime and can be regulated by changing the doping concentration. Our investigation establishes a direct relationship between the electronic band structure of monolayer ${\mathrm{Zr}\mathrm{Te}}_5$ and its anisotropic optical properties, which in turn influence the characteristics of hyperbolic SPPs. The presence of a relative broadband hyperbolic region, a high quality factor (${\gamma }^{-1}$), and a tunable propagation direction of SPPs in monolayer ${\mathrm{Zr}\mathrm{Te}}_5$ open a new avenue for applications in advanced optical devices.

Extreme sound absorption at the microscale presents significant challenges in acoustic systems. Here, we propose and experimentally validate a theoretical model for extreme-scale sound absorption in microscale thin-walled resonators (MTWR). By leveraging the mechanisms of viscous and thermal losses, the model achieves the minimum cross-sectional dimensions permitted by manufacturing constraints. Specifically, at the microscale, we have designed a resonator with cross-sectional dimensions (≤2 mm) and wall thickness (≤300 µm). Loss equations and analytical models are employed to systematically determine the optimal cross-sectional dimensions for sound absorption and uncover the physical mechanisms in microscale narrow tube resonators. Theoretical analysis and numerical simulations reveal the acoustic performance of single and multiple Fabry-Pérot coupled resonators, achieving broadband, quasiperfect absorption of incident acoustic waves through the mechanism of weakly coupled resonance. Our finding demonstrates the potential of thin-walled resonators to achieve extreme sound absorption at the microscale.

Sublinear resonant deviations from an exceptional point degeneracy (EPD) has been recently promoted as a sensing scheme. However, there is still an ongoing debate whether the sensitivity advantage is negated by an increase in fundamental noise—especially when active elements induce self-oscillations. In this case, nonlinearities are crucial in stabilizing amplifying modes and mitigating noise effects. A drawback is the formation of hysteresis loops that signal a transition to unstable modes. This can only be alleviated by precise cavity symmetry management. Here, utilizing two coupled nonlinear RLC tanks with balanced amplification and attenuation, we demonstrate that an explicit symmetry violation, induced by sweeping the resonant detuning of the RLC tanks, reveals a hysteresis loop near the EPD whose width scales sublinearly with the intertank coupling. Our proposal re-envisions this disadvantageous feature as a sensing protocol with diverging sensitivity, enhanced signal-to-noise ratio, and self-calibration without requiring delicate symmetry control. As such, it opens avenues in metrology as well as for optical and rf switching and triggering.

Quantum process tomography (QPT) is the gold standard for fully characterizing quantum processes, yet it is resource intensive. In this work, we shift our focus from global to local quantum processes, which are beneficial for practical scenarios, such as distributed quantum computing and quantum networks. We term these local processes as reduced quantum processes and present a comprehensive theory to describe them. To experimentally characterize all $k$-reduced quantum processes of an $n$-qubit quantum process, we introduce our primary method, quantum process overlapping tomography (QPOT), and compare it with two alternative approaches: ancilla QPT and parallel QPT. Suppose the target quantum process involves $T$ local interactions, each acting on $l_i$ qubits, with the total number of affected qubits satisfying $l:=\sum _{i=1}^T{l}_i\le n$. The experimental configurations required for each method are as follows: QPOT requires $2^l\times e^{\mathcal{O}(k)}\times \log (n)$ experimental configurations. Ancilla QPT requires $e^{\mathcal{O}(k)}\times \log (2n)$ experimental configurations but additionally demands $n$ ancilla qubits and the preparation of maximally entangled states. Parallel QPT requires approximately $\sum _{i=1}^{n^k}{2}^{m_i}\times {12}^k$ experimental configurations, where $m_i$ denotes the number of qubits interacting with the $i\mathrm{th}$ reduced quantum process. Among these methods, QPOT exhibits superior efficiency and broader applicability. The efficacy of our methods is confirmed through experimental demonstrations conducted on IBM hardware, aligning well with our theory.

Realization of the optical pascal has been limited by systematic errors caused by distortion of the optic. In this work, distortion error is circumvented via synchronous measurement of helium refractivity at two optical frequencies. The resultant pressure realization achieves combined standard uncertainty of $5.7\times {10}^{-6}p$, chiefly limited by ab initio knowledge of helium dispersion. Two-color measurements are also presented for neon, argon, and nitrogen, which enable semiprimary realization of the pascal in a more practical embodiment. For argon dispersion, measurement and ab initio calculation barely agree within mutual expanded uncertainty; experiment is about 16 times more accurate than theory.

In the search for novel photovoltaic (PV) solar materials, half-Heusler (hH) compounds have recently been regarded as especially promising due to their favorable electronic and optical properties. Using first-principles density-functional theory and many-body excited-state calculations, we study the quasiparticle band structure, as well as the optical and excitonic properties, of two representative hH compounds, namely, $\mathrm{Li}\mathrm{Zn}\mathrm{As}$ and $\mathrm{Sc}\mathrm{Ag}\mathrm{C}$, for PV applications. Our results reveal a direct-band-gap semiconducting behavior in $\mathrm{Li}\mathrm{Zn}\mathrm{As}$ ($\mathrm{Sc}\mathrm{Ag}\mathrm{C}$) with a value of approximately 1.5 (1.0) eV under the accurate $G_0{W}_0$ method. The highest value of the imaginary part of the dielectric function is found to be approximately 52 (87), 77 (87), and 88 (91) using the independent-quasiparticle approximation, local field effects in the random-phase approximation, and the electron-hole interaction within the Bethe-Salpeter equation, respectively. Both materials demonstrate a high refractive index, high absorption coefficients (approximately $1.2–1.6\times {10}^6{\mathrm{cm}}^{-1}$), and low reflectivity (less than 40%) within the active region of the solar energy spectrum. The triply degenerate bright excitons (exciton A) at the main absorption peak, as well as a considerable number of bright excitonic states in the visible region, are observed; however, the oscillator strengths of the excitons are comparatively weaker in $\mathrm{Sc}\mathrm{Ag}\mathrm{C}$ than in $\mathrm{Li}\mathrm{Zn}\mathrm{As}$. We further discuss the exciton character contributing to intense optical interband transitions and reveal that the direct optical band gap is associated with the loosely bound exciton A state with a binding energy of approximately 45 (56) meV in $\mathrm{Li}\mathrm{Zn}\mathrm{As}$ ($\mathrm{Sc}\mathrm{Ag}\mathrm{C}$). Exciton A is found to be highly localized (delocalized) in momentum (real) space, indicating the presence of Mott-Wannier–type excitons at the band gap. Finally, we assess the solar efficiencies using the spectroscopic limited maximum efficiency (SLME) model and find SLME values of approximately 32% for $\mathrm{Li}\mathrm{Zn}\mathrm{As}$ and approximately 31% for $\mathrm{Sc}\mathrm{Ag}\mathrm{C}$ at an approximately 0.4 $\text{μ}\mathrm{m}$ thin-film thickness. These findings highlight the significant role of excitons in the solar energy absorption process and also suggest that both are highly suitable candidates for next-generation single-junction thin-film PV solar devices.

The electrical breakdown of ${\mathrm{SF}}_6$ in the presence of floating metal particles is facilitated by two key factors: the role of floating metal particles and the nonlinear breakdown behavior of high-pressure ${\mathrm{SF}}_6$. However, the microscopic transient processes remain unclear, motivating this paper. Using two-dimensional fluid models, we investigate ${\mathrm{SF}}_6$ streamer breakdown induced by a floating linear metal particle under negative applied voltage. First, we identify a characteristic double-end streamer inception in the combined gap. Then, we propose the following-streamer (FS) mechanism to explain the metal particle’s role. Two following streamers, FS1 and FS2, arise from the interaction between space charge and metal particle. FS1 facilitates breakdown via the negative space-charge field generated by its head. FS2 facilitates breakdown by merging with FS1, accelerating its propagation and enhancing the electric field at the primary streamer head. Finally, we propose the side-streamer (SS) mechanism to explain the nonlinear breakdown behavior of high-pressure ${\mathrm{SF}}_6$. The SS is identified as a new forward ionization wave that develops along the sides of the primary streamer, due to photoionization-driven negative-ion accumulation. SS facilitates breakdown by merging with the primary streamer, increasing negative space charge and leading to three distinct propagation modes. Higher pressure increases the production rate of negative ions along the streamer sides, making SS more likely to form. Under overvoltage, the facilitating effect of SS diminishes as the background field $(E/N{)}_b$ strengthens, disappearing when $(E/N{)}_b$ exceeds 245 Td. This study provides new insights into the ${\mathrm{SF}}_6$ streamer breakdown mechanisms induced by floating metal particles and offers theoretical references for further investigation on the quantitative characterization.

We demonstrate laser-induced relaxation oscillations in superconducting nanowire single-photon detectors (SNSPDs). These oscillations appear when a voltage-biased $\mathrm{Nb}\mathrm{Ti}\mathrm{N}$ nanobridge detector is illuminated with intense pulsed-laser light at a repetition rate of approximately $19\mathrm{MHz}$. They differ from the well-known relaxation oscillations by a stepwise increase in frequency and phase locking of the oscillations to the laser pulses. We create a model that incorporates electrical feedback and excludes thermal effects to simulate and explain the origin of the observed laser-induced relaxation oscillations. Qualitative agreement to the experiment is achieved using realistic values for the parameters in the model.

Weak measurement is an effective technique for detecting the photonic spin Hall effect (SHE), but its performance is limited under strong coupling conditions or when the preselected and postselected states are nearly orthogonal. While modified weak measurements have been proposed to address these issues, the formation mechanism of the amplified displacements remains unclear, potentially impacting practical reliability. Therefore, exploring alternative methods for detecting the photonic SHE to compensate for the shortcomings of existing techniques is significant. In this paper, we develop a differential interference method to detect the photonic SHE. By leveraging differential interference, we reestablish the relationship between spin-dependent displacements and amplified displacements and elucidate the formation mechanism of the amplified displacements. We find that the measurement procedure using preselected and postselected ensembles is still effective. We compare the theoretical models of differential interference, conventional weak measurements, and modified weak measurements. We show that the experimental results coincide with the predictions of the differential interference theory. Due to the amplification effect of differential interference, the measurement resolution reaches ${10}^{-7}$ rad at small incidence angles, outperforming conventional polarimeters. Our method offers an alternative to weak measurement techniques for detecting the photonic SHE and holds promise for precision measurement.

Room-temperature photonic crystals (PCs) in the optical frequency range have been widely studied and applied, while those in the microwave frequency range have received relatively less attention, as quantum interferences of microwaves is strongly suppressed at room temperature. In this work, we study the quantum scattering of microwave photons by periodically arranged emitters. We experimentally demonstrated two kinds of microwave PCs generated by periodically arranged microwave cavities and Josephson two-level atoms. We investigate how the bandwidth and central frequency of the generated band gap are influenced by the scattering defects, the dissipation of the scatterers, the photon-scatter coupling strengths, and the separated distances between the nearest-neighbor scatterers. In particular, we show that the central frequency of the band gap generated by the current biased Josephson-junction (CBJJ) array can be dynamically controlled by adjusting the biased dc current. The microwave PCs with controllable band gaps demonstrated here can be applied for microwave quantum information processing.

Experimental results on the effect of spin pumping in yttrium iron garnet magnonic crystal-platinum structure are considered. The voltage induced in the platinum due to spin pumping and the inverse spin Hall effect was found to possess the oscillations at Bragg resonances. We discuss the origin of such oscillations and attribute them to the respective behavior of the density of states for spin waves. It is revealed that a multimode spectrum of the spin waves can lead to the formation of Bragg resonances due to intermodal interaction and such resonances can affect spin pumping as well. The obtained results show that magnonic crystals can be used to arrange the frequency response of spin pumping.

Nonlinear magnetic interactions provide access to complex quantum spin dynamics and thus enable the study of intriguing physical phenomena. However, these interactions are often dominated by the linear Zeeman effect, which can complicate system dynamics and make their analysis more challenging. In this article, we theoretically and experimentally introduce a method to induce the quadratic Zeeman effect while effectively compensating for its linear counterpart. By isolating the quadratic Zeeman contributions, we demonstrate and analyze controlled superposition generation between specific magnetic sublevels in room-temperature rubidium-87 atoms. This study opens avenues for controlling any spin system, regardless of its total angular momentum.