In response to the growing demand for more efficient and compact refrigeration and energy conversion devices, electrocaloric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) is among the most promising active substances. However, despite its high electrocaloric response, the maximum efficiency achievable over a cooling cycle is hampered by losses. To overcome this major limitation, losses have been reduced by using an electrothermal poling treatment as well as by controlling the surface roughness. The upper bound of the efficiency computed over a thermodynamic cycle mimicking the working conditions of an actual cooling device is increased from 1% to 10% of the Carnot efficiency. This represents a major improvement in enhancing ferroelectric materials for advanced energy applications.

It is a common requirement to lock the frequency of a laser to an optical cavity resonance in experimental physics research. While the Pound-Drever-Hall technique is among the most popular methods, it requires the use of auxiliary phase modulators, which increases the complexity and cost. Moreover, the laser-locking noise caused by unwanted residual amplitude modulation within the modulator often limits the achievable locking stability. In this work, we demonstrate an alternative approach that negates the need for any external modulators, and inherently mitigates the residual amplitude noise. We directly apply fast electro-optic modulation to a monolithic lithium niobate microresonator to efficiently generate laser sidebands at frequencies much higher than the optical resonance bandwidth. Such a modulation allows us to generate low-noise laser-locking signals after appropriate photodetection and demodulation. Our noise characterization and frequency instability measurement show that the direct modulation technique renders a locking instability that is one order of magnitude better than that of the conventional Pound-Drever-Hall technique. The residual locking instability is also numerically analyzed and experimentally verified.

Continuous-variable entangled radiation known as Einstein-Podolsky-Rosen (EPR) states are spatially separated quantum states with applications ranging from quantum teleportation and communication to quantum sensing. The ability to efficiently generate and harness EPR states is vital for advancements in quantum technologies, particularly in the microwave domain. Here, we introduce a kinetic inductance quantum-limited amplifier that generates stationary-path-entangled microwave radiation. Unlike traditional Josephson junction circuits, our design offers simplified fabrication and operational advantages. By generating single-mode squeezed states and distributing them to different ports of a microwave resonator, we deterministically create distributed entangled states at the output of the resonator. In addition to the experimental verification of entanglement, we present a simple theoretical model using a beam-splitter picture to describe the generation of path-entangled states in kinetic inductance superconducting circuits. This work highlights the potential of kinetic inductance parametric amplifiers as promising technology for practical applications such as quantum teleportation, distributed quantum computing, and enhanced quantum sensing. Moreover, it can contribute to foundational tests of quantum mechanics and advances in next-generation quantum information technologies.

The unidirectional manipulation of sound propagation is crucial for developing nonreciprocal devices, as it efficiently enhances application performance by preventing interference. In this work, we propose a design for a topologically protected nonreciprocal splitter for acoustic waves, utilizing the anomalous feature of dual edge-localized, unidirectional parallel transmission. Our design integrates two opposite modified-Haldane-type acoustic crystals, whose unit cell consists of two ring resonators with staggered airflow circulation, to orchestrate the splitting mechanism. We show distinctive phenomena, including tilted edge bands and copropagating one-way edge-localized acoustic wave propagation via simulations. The nonreciprocal splitting behavior is further demonstrated by the bidirectional propagation along edges of the input acoustic wave at the interface. Additionally, we leverage its functionality to independently transmit two channels of different acoustic information. Our findings not only provide a viable scheme of experimental implementation, but also open avenues for expanding the application of topologically protected antichiral edge states in acoustic communication.

The analysis presented in this paper results in new formulas for the Urbach tail parameter, which are supposed to be valid for III-V compounds. They were derived based on numerical simulations performed with the nonequilibrium Green’s function method applied to the multiband $\mathbf{k}\cdot \mathbf{p}$ Hamiltonian of bulk material. The influence of static and dynamic disorders on the band tailing process was examined in relation to the scatterings of free carriers with longitudinal-optical (LO) phonons and ionized impurities. In this case, the disorder potentials just add to the unperturbed potential, which results in a perturbed density of states (DOS). The latter takes on exponential shape as a result of the superposition of sidebands, produced by the potential of the LO phonons. The Urbach parameter, which is the exponent of the perturbed DOS, is then proportional to the logarithm of the perturbation. This results in a modest temperature dependence of this parameter, which was observed for various III-V compounds. Moreover, the absolute values of the Urbach parameter, predicted by the present “scattering” approach, remain in reasonable agreement with experimental data reported in the literature. The range of doping densities studied extends to heavy ones; therefore, the results of this paper are crucial for addressing a current challenge in the semiconductor industry, namely the reduction of the subthreshold swing in tunneling field-effect transistors, which are considered potential future solutions for efficient, low-power logic switches.

Ultrashort spin-polarized electron pulses, generated through optically driven ultrafast demagnetization, have demonstrated high efficiency in achieving magnetization reversal of a ferromagnetic layer within a few hundred femtoseconds. Previous studies have focused on magnetization reversal in perpendicularly magnetized spin valves, where the static magnetization configuration and its dynamics are strongly influenced by the substantial demagnetization field inherent in this geometry. Consequently, the impact of layer thickness on the reversal process in such configurations presents a significant challenge and has been rarely studied. Here, we investigate in-plane magnetized $\mathrm{Gd}\mathrm{Co}/\mathrm{Cu}$/ferromagnetic layer spin valves in relation to isolating the impact of the Curie temperature and the ferromagnetic layer thickness on magnetization switching. We demonstrate that the threshold laser fluence necessary for reversing the ferromagnetic layer increases with the Curie temperature and the ferromagnetic layer thickness. Additionally, our findings indicate that achieving complete reversal may require multiple pulses, with the number of pulses needed increasing with the Curie temperature and the thickness of the ferromagnetic layer. The maximum thickness of the ferromagnetic layer that allows for full reversal is limited by the $\mathrm{Gd}$ concentration in the $\mathrm{Gd}\mathrm{Co}$ spin current source layer. These results enhance our understanding of ultrafast magnetization reversal induced by ultrafast spin pumping and offer valuable insights for designing energy-efficient magnetic memory devices.

The in-flow focusing method, introduced herein, enables rapid and straightforward measurements of the whole-channel acoustic energy of acoustic flow-through devices. The method is applied to assess the whole-channel acoustic energy and acoustophoretic efficiency frequency spectra of a bottom-actuated silicon-glass and a side-actuated glass chip. The input variables are the time-independent geometrical shape of the particle trajectories along the manipulation chamber, the channel cross-section geometry, the physical properties of the reference particles and fluid, and the volumetric flowrate. The outputs are the total acoustic energy, the acoustophoretic efficiency, as well as the acoustic energy density distribution along the channel, which provide a comprehensive overview of the performance of acoustically driven lab-on-a-chip setups. The acoustophoretic efficiency is an important parameter that relates the energy dissipation, and therefore the heat development in the device, to the useful acoustic energy in the channel. Unlike the current state-of-the-art methods such as particle image velocimetry, particle tracking velocimetry, and optical trapping, which are typically limited to small channel areas and are time-consuming, the in-flow focusing method can be applied to long channels and enables rapid measurements of the whole-channel acoustic energy.

Laser-intensity fluctuations cause undesired phase noise even in balanced heterodyne interferometers. However, in space missions in particular, such as LISA Pathfinder or LISA, direct measurements of these fluctuations at the relevant frequencies are often not available. Hence, it can be challenging to estimate their impact on the interference phase. To address this, we propose a new method for characterizing laser relative intensity noise (RIN) using differential wavefront sensing (DWS), with the latter being a well-established technique typically used for angular sensing and control. Unlike other methods, this approach does not require an additional reference interferometer and instead takes advantage of the inherent phase subtraction of DWS. This allows us to estimate the RIN value at the heterodyne frequency and its harmonic, relative to the sensor noise floor of the total measurement system. Moreover, it provides a strategy to identify the ideal set point for minimizing RIN couplings in DWS.

Although indium vanadate (${\mathrm{InVO}}_4$) is an excellent n-type semiconductor, a controlled n-type carrier concentration of the ${\mathrm{InVO}}_4$ photocatalyst is required to enhance its photocatalytic activity. This study systematically explores the self-consistent Fermi energies, dominant intrinsic defects, electron concentration ($n_0$), and defect concentration of ${\mathrm{InVO}}_4$ using density-functional theory coupled with detailed thermodynamic equilibrium simulations. The results indicate that the ${\mathrm{V}}_{\mathrm{In}}$ antisite defect (the vanadium atom replacing the indium atom) is the dominant intrinsic defect in ${\mathrm{InVO}}_4$. The calculated Fermi energy pinning position indicates that ${\mathrm{InVO}}_4$ has n-type doping behavior from intrinsic defects under $\mathrm{O}$-poor growth conditions, consistent with the experiments. Interestingly, donor ($D^{+}$) doping is positive for improving the $n_0$ of the intrinsic-defect-doped ${\mathrm{InVO}}_4$. Therefore, at 300 K, a broad optimized chemical potential region (OCPR) is obtained for ${\mathrm{InVO}}_4$ codoped with donors and intrinsic defects. In this OCPR, the $n_0$ is higher, without recombination centers and significant compensation, significantly enhancing the photocatalytic activity of ${\mathrm{InVO}}_4$. However, for the case of growth temperature at 873 K and after quenching from 873 to 300 K, the OCPR is much narrower than that at 300 K, indicating that higher temperatures may adversely affect the OCPR. Our results provide deep insights into defect behaviors in ${\mathrm{InVO}}_4$ and suggest strategies for enhancing its n-type conductivity properties, offering new opportunities for manipulating the photocatalytic performance of ${\mathrm{InVO}}_4$.

The Seebeck effect, as a form of sustainable energy, can convert waste heat into useful electric energy. It is highly desirable to design a compact thermoelectric module that integrates a high density of miniature thermoelectric components with high Seebeck coefficients. The conventional solid-state Seebeck effect produces voltage through the nonequilibrium distribution of electrons owing to temperature gradients. In this research, we have designed thermoelectric nanojunctions formed by nickel-ion-chelated DNA nanowires. These junctions have led to the discovery of a highly efficient Seebeck effect, which is assisted by the charging and discharging of the nickel ions utilizing the reversible redox reaction. The reversible redox reaction significantly enhances the Seebeck coefficients. Our theory, with parameters supported by the results of our experiments, predicts that the biomimicry thermopower mechanisms could generate giant Seebeck coefficients at a value larger than ${10}^5$ µV/K. The dynamic Seebeck effects observed in $\mathrm{Ni}$-DNA junctions could inspire the exploration of solid-state thermoelectric materials with similar working mechanisms, potentially useful in nanotechnology and green energy.

Microcalorimeters that leverage microwave kinetic inductance detectors to read out phonon signals in the particle-absorbing target, referred to as kinetic inductance phonon-mediated (KIPM) detectors, offer an attractive detector architecture to probe dark matter (DM) down to the fermionic thermal relic mass limit. A prototype KIPM detector featuring a single aluminum resonator patterned onto a 1-gram silicon substrate was operated in the Northwestern EXerimental Underground Site (NEXUS) low-background facility at Fermilab for characterization and evaluation of this detector architecture’s efficacy for a DM search. An energy calibration was performed by exposing the bare substrate to a pulsed source of 470-nm photons, resulting in a baseline resolution on the energy absorbed by the phonon sensor of $2.1\pm 0.2$ eV, a factor of two better than the current state of the art, enabled by quasiparticle lifetimes extending up to 6.5 ms. However, due to the subpercent phonon collection efficiency, the resolution on energy deposited in the substrate is limited to ${\sigma }_E=318\pm 29$ eV. We further model both the signal pulse shape as a function of device temperature to extract quasiparticle lifetimes, and the observed noise spectra.

The classical scenario where a single-plane-wave field impinges a Dallenbach absorber is well studied both theoretically and experimentally. However, occasionally a spectrum of plane waves impinges the absorber. Such a scenario occurs, for example, if an antenna is located adjacent to the absorbing layer. In this paper, for this scenario we obtain the absorbing performance bound and design an optimized layered absorber that approaches the bound. In a numerical demonstration, we explore a realistic case where a dipole antenna is placed in the vicinity of a finite, electrically thin, Dallenbach absorber backed by a perfect-electric-conductor plane in the 6G frequency range. In the absence of the absorbing layer covering the perfect-electric-conductor plane, severe scattering from the plane distorts the radiated fields. These distortions are robustly mitigated by the specifically tailored optimal absorber to yield a more-desired radiation pattern. Additionally, we propose a metamaterial realization that emulates the required properties of the absorbing layer for all field polarizations.

The topological semimetal ${\text{CrPt}}_3$ has potential for generating unconventional spin torques due to its ferrimagnetic ordering, topological band structure, and high anomalous Hall effect. ${\text{CrPt}}_3$ exhibits ferrimagnetic behavior only in its chemically ordered phase and is paramagnetic in its chemically disordered phase. By controlling the growth and annealing temperatures, we prepare epitaxial films of both chemically ordered and chemically disordered phases of ${\text{CrPt}}_3$, allowing us to investigate the effect of magnetic ordering on unconventional-torque generation. We use angle-dependent spin-torque-ferromagnetic-resonance and second-harmonic Hall measurements to probe the spin torques generated from epitaxial ${\text{CrPt}}_3$ in ${\text{CrPt}}_3/\mathrm{Cu}/{\text{Ni}}_{81}{\text{Fe}}_{19}$ heterostructures. With current applied along specific directions with respect to the crystal order, we reveal unconventional spin torques in both ordered and disordered films. When current flows parallel to the $[1\overline{1}1]$ and $[\overline{1}11]$ directions, we observe an unconventional fieldlike torque that is opposite in sign for the two directions. Our calculations reveal that this unconventional torque originates from an indirect nonlocal spin-orbit torque due to spin scattering at the ${\text{CrPt}}_3/\mathrm{Cu}$ interface, in addition to symmetry breaking at this interface.

We investigate the complex conductivity of superconductors under a direct-current (dc) bias based on the well-established Keldysh-Eilenberger formalism of nonequilibrium superconductivity. This robust framework allows us to account for the Higgs mode and impurity-scattering self-energy corrections, which are now known to significantly impact the complex conductivity under a bias dc, especially near the resonance frequency of the Higgs mode. The purpose of this paper is to explore the effects of these contributions on the low-frequency complex conductivity relevant to superconducting device technologies. We begin by nonperturbatively calculating the equilibrium Green’s functions under a bias dc, followed by an analysis of the time-dependent perturbative components. This approach enables us to derive the complex conductivity formula for superconductors ranging from clean to dirty limits, applicable to any bias dc strength. We validate our theoretical approach by reproducing known results and experimentally observed features, such as the characteristic peak in ${\sigma }_1$ and the dip in ${\sigma }_2$ attributed to the Higgs mode. Our calculations reveal that the Higgs mode and impurity-scattering self-energy corrections significantly affect the complex conductivity even at low frequencies ($\hslash \omega \ll \mathrm{\Delta }$), relevant to superconducting device technologies. Specifically, we find that the real part of the low-frequency complex conductivity, ${\sigma }_1$, exhibits a bias-dependent reduction up to $\hslash \omega \sim 0.1$, a much higher frequency than previously considered. This finding allows for the suppression of dissipation in devices by tuning the bias dc. Additionally, through the calculation of the imaginary part of the complex conductivity, ${\sigma }_2$, we evaluate the bias-dependent kinetic inductance for superconductors ranging from clean to dirty limits. The bias dependence becomes stronger as the mean free path decreases. Our dirty-limit results coincide with previous studies based on the oscillating superfluid density (the so-called slow experiment) scenario. This widely used scenario can be understood as a phenomenological implementation of the Higgs mode into the kinetic inductance calculation, now justified by our calculation based on the robust theory of nonequilibrium superconductivity, which microscopically treats the Higgs-mode contribution. These results highlight the importance of considering the Higgs mode and impurity-scattering self-energy corrections in the design and optimization of superconducting devices under a bias dc.

Quantum mechanics has greatly impacted our understanding of microscopic nature. One of the key concepts of this theory is generalized measurements, which have proven useful in various quantum information processing tasks. However, despite their significance, they have not yet been shown empirically to provide an advantage in quantum randomness certification and expansion protocols. This investigation explores scenarios where generalized measurements can yield more than 1 bit of certified randomness with a single-qubit system measurement on untrusted devices and against a quantum adversary. We compare the robustness of several protocols to exhibit the advantage of exploiting generalized measurements. In our analysis of experimental data, we were able to obtain 1.21 bits of min-entropy from a measurement taken on one qubit of an entangled state. We also obtained 1.07 bits of min-entropy from an experiment with quantum state preparation and generalized measurement on a single qubit. We also provide finite data analysis for a protocol using generalized measurements and the Entropy Accumulation Theorem. Our exploration demonstrates the potential of generalized measurements to improve the certification of quantum sources of randomness and enhance the security of quantum cryptographic protocols and other areas of quantum information.