Mirror symmetry is among the most fundamental concepts of physics, and its spontaneous breaking at the molecular level allows chiral molecules to exist in two enantiomers that are mirror images of each other. The majority of the chiro-optical effects routinely used to detect enantiomers in mixtures, such as circular dichroism, rely on chiral sensitivity to photon circular polarization, and thus do not harness the full potential of mirror-symmetry breaking, which also involves the spatial profile of the radiation. Here we show that the parity indefiniteness of an electromagnetic field interacting with chiral matter supports mirror optical activity, a chiro-optical effect where a chiral film, when it is probed by the mirror-symmetric field of a nanoemitter, produces a near field whose spatial profile has broken mirror symmetry. The detection of near-field dissymmetry can provide an efficient chiral sensing technique. We specialize the discussion to nanofilms with infrared chirality by using a swift electron in an aloof configuration as the nanoemitter and an off-axis transparent conducting nanoparticle as the near-field probe; the spatial dissymmetry factor of the nanoparticle cathodoluminescence is 1 order of magnitude larger than the dimensionless circular dichroism, and is further enhanced to 2 orders of magnitude if an additional graphene sheet is deposited on the film interface.

Nonground eigenvalues are widely disregarded in magnetic resonance relaxation measurements of porous media due to difficulties involved in their measurement, detection, and the derivation of physically meaningful parameters from them. Such nonground eigenvalues may be experimentally observed in relaxation measurements, such as the relaxation correlation of $T_1-T_2$, and yield information on the pore size and surface relaxivity of porous media without calibration through other independent measurements. Nonground eigenvalue analysis of $T_1-T_2$ measurements on Berea sandstone undertaken at three static magnetic fields produces pore sizes consistent with those obtained through x-ray microtomography and SEM measurements. Similar agreement is found for a Bentheimer sandstone with a more complex pore geometry. A phase-encoding imaging variant of this method measures the imbibition confinement-size profile in Berea sandstone. It is suggested that the existence of nonground eigenmodes may be much more prevalent in simple magnetic resonance relaxation measurements than previously considered. Therefore, it is possible to measure pore size by matching numerical Brownstein-Tarr solutions with those of experiments in a wide variety of samples and magnetic resonance methods.

The 5d transition-metal oxides are an intriguing platform to demonstrate efficient charge-to-spin-current conversion due to a unique electronic structure dominated by strong spin-orbit coupling. Here, we report on the stacking-order effect of spin-orbit torque (SOT), spin-Hall magnetoresistance, and magnetic anisotropy in bilayer ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$-5d iridium oxide, ${\mathrm{Ir}\mathrm{O}}_2$. While all ${\mathrm{Ir}\mathrm{O}}_2$ and $\mathrm{Pt}$ control samples exhibit large dampinglike SOT generation, stemming from the efficient charge-to-spin-current conversion, the magnitude of the SOT is larger in the ${\mathrm{Ir}\mathrm{O}}_2$($\mathrm{Pt})$ bottom sample than in the ${\mathrm{Ir}\mathrm{O}}_2$($\mathrm{Pt})$ top one. The fieldlike SOT has an even more significant stacking-order effect, resulting in an opposite sign in the ${\mathrm{Ir}\mathrm{O}}_2$ samples in contrast to the same sign in the $\mathrm{Pt}$ samples. Furthermore, we observe that the magnetic anisotropy energy density and the anomalous Hall effect are increased in the ${\mathrm{Ir}\mathrm{O}}_2$($\mathrm{Pt})$ bottom sample, suggesting enhanced interfacial perpendicular magnetic anisotropy. Our findings highlight the significant influence of the stacking order on spin transport and the magnetotransport properties of $\mathrm{Ir}$ oxide-ferromagnet systems, providing useful information for the design of SOT devices, including 5d transition-metal oxides.

We investigate temperature-dependent magnetization reversal of $\mathrm{Co}\mathrm{Ru}$ graded films, in which a predefined depth-dependent exchange-coupling strength J follows a V-shaped profile. Magnetometry reveals an extended temperature range below the Curie temperature $T_C$ where the reversal of the magnetization M is not accompanied by the conventionally occurring hysteresis, in stark contrast with homogeneous $\mathrm{Cr}\mathrm{Ru}$ reference films. This is caused by the temperature-driven paramagnetic (PM)-ferromagnetic (FM) phase transition, which does not occur in the entirety of the graded material but only in well-defined nanoscopic regions at any given temperature, enabling the creation of two internal PM/FM interfaces that assist the external magnetic field in reversing the magnetization of the FM graded sample region. Hysteretic reversal is recovered at sufficiently low sample temperatures or by using graded structures with very steep J gradients, so that no PM/FM interfaces form inside the exchange-coupled layer material that could influence the magnetization reversal process. Our findings open interesting material design options, and we envision wide application potential, since we succeed in engineering a temperature gap between the temperature dependent magnetization and hysteresis onsets, a capability of interest for any technology benefitting from field-free magnetization switching.

The Fermi-Dirac statistics is adopted to consider degenerate effects in organic diodes. The degenerate drift-diffusion equation is analytically solved under the uniform-electrical-field approximation. The analytical expressions for the current-voltage relationship and carrier density are derived. The mobility model of Pasveer [Pasveer et al., Phys. Rev. Lett. 94, 206601 (2005)] is improved to consider correct characteristic length scales and combined with the analytical solution to analyze the properties of six organic diodes. The theoretical results are in good agreement with experimental data. Six model parameters are extracted for six devices, namely, the parameters $N_0$ and σ for the density of states; the parameters ${\mu }_0$ and a for the mobility model; and the potential barriers $W_{\mathrm{an}}$ and $W_{\mathrm{cat}}$ at the anode and cathode, respectively. The degenerate parameter $\overline{\eta }$ at 300 K is deduced. It is shown that two materials, MEH-PPV and F8BT, are degenerate. Although four other materials can be treated as nondegenerate, the degenerate effects are not negligible near the anode region.

We describe and operate a spin-magnetometer based on the phase modulation of cavity magnon polaritons. In this scheme a rf magnetic field is detected through the sidebands it induces on a pump, and the experimental configuration allows for a negligible pump noise and a high-frequency readout. The demonstrator setup, based on a copper cavity coupled to an yttrium iron garnet sphere hybrid system, reached a sensitivity of $2.0\mathrm{pT}/\sqrt{\mathrm{Hz}}$ at 220 MHz, evading the pump noise and matching the theoretical predictions. An optimized setup can attain a rf magnetic field sensitivity of about $8\mathrm{fT}/\sqrt{\mathrm{Hz}}$ at room temperature. An orders of magnitude improvement is expected at lower temperatures, making this instrument one of the few magnetometers accessing the subfemtotesla limit.

The magnon spin Nernst effect was recently proposed as an intrinsic effect in antiferromagnets, where spin diffusion and boundary spin transmission have been ignored. However, diffusion processes are essential for converting a bulk spin current into boundary spin accumulation, which determines the spin injection rate into detectors through imperfect transmission. We formulate a diffusive theory to describe the detection of the magnon spin Nernst effect with boundary conditions reflecting real device geometry. Because of the spin diffusion effect, the output signals in both electronic and optical detection grow rapidly with increasing system size in the transverse dimension, which eventually saturate. Counterintuitively, the measurable signals are even functions of magnetic field, making optical detection more favorable than electronic detection.

We study a direct-current-driven maser device enabled by spin-photon coupling, where coherent magnetic self-oscillation can be realized in a large-area ferromagnetic thin film under the excitation of spin-orbit torques. We show via both micromagnetic simulation and analytical derivation that above a critical value of the coupling strength between the spin-torque oscillator and the microwave resonator, magnetic oscillation develops macroscopic phase coherence, a narrow linewidth, and becomes phase-locked with the photon mode. The threshold coupling strength for synchronizing individual spins reduces as the sample dimension increases, suggesting that the spin-torque-oscillator maser can be readily realized using large-area thin-film ferromagnets without relying on dimension confinement. Moreover, the photon mode can directly provide microwave emission, which exhibits enhanced power and a reduced linewidth with an increasing number of spins, leading to a useful approach for developing highly coherent on-chip microwave sources.

Beam forming using phased arrays forms the basis of several sonar communication and biomedical imaging techniques. However, to date, such arrays remain constrained by wave reciprocity in addition to being confined to their operational frequency; two limitations that have severely hindered imaginative advancements in this domain. In the context of sound propagation, nonreciprocity typically refers to unidirectional elastic and surface acoustic wave devices. However, a breakage of reciprocity in phased arrays manifests itself in reception and transmission patterns, which can be independently tuned, which has thus far been elusive. This work reports on a class of nonreciprocal phased arrays, which operate independently and simultaneously within different directions and frequency channels, thus breaking transmission-reception symmetry and offering enhanced capabilities in guided wave engineering. The system comprises an array of transceiving piezoelectric wafer discs bonded to an elastic medium and incorporates a prescribed dynamic modulation on top of a static phase gradient, which enables concurrent phononic transitions in energy and momentum spaces that mitigate the constraints imposed by Lorentz reciprocity. Following the theory and predictive analysis, the entire array and its associated capabilities are demonstrated experimentally.

We study the minimal recurrent spiking neural network of a single neuron with an autaptic synapse. We implement the neural system in the solid state with a recently introduced ultracompact neuron (UCN) model, which is based on the memristive properties of a thyristor. The UCN is supplemented by a self-synaptic, autaptic, connection, where we control the feedback. Both excitatory and inhibitory cases are considered. We explore the systematic behavior as a function of autaptic intensity and feedback time delay. We realize a tunable dynamic memory, showing graded persistent activity, where short excitatory and inhibitory pulses allow the firing rate to be controlled. We finally reproduce recent experimentally observed behavior of a biological autapse measured in vivo, finding excellent qualitative agreement. Our work opens the way into the field of solid-state neuroscience, with the UCN as an accessible platform to implement and experimentally study the dynamic behavior of spiking neural networks.

We experimentally achieve wave-mode conversion and rainbow trapping in an elastic waveguide loaded with an array of resonators. Rainbow trapping is a phenomenon that induces wave confinement as a result of a spatial variation of the wave velocity, here promoted by gently varying the length of consecutive resonators. By breaking the geometrical symmetry of the waveguide, we combine the wave-speed reduction with a reflection mechanism that mode converts flexural waves impinging on the array into torsional waves traveling in opposite directions. The framework presented herein may open opportunities in the context of wave manipulation through the realization of structural components with concurrent wave-conversion and energy-trapping capabilities.

State-of-the-art organic solar cells exhibit power conversion efficiencies of 18% and above. These devices benefit from the suppression of free charge recombination with regard to the Langevin limit of charge encounter in a homogeneous medium. It is recognized that the main cause of suppressed free charge recombination is the reformation and resplitting of charge-transfer (CT) states at the interface between donor and acceptor domains. Here, we use kinetic Monte Carlo simulations to understand the interplay between free charge motion and recombination in an energetically disordered phase-separated donor-acceptor blend. We identify conditions for encounter-dominated and resplitting-dominated recombination. In the former regime, recombination is proportional to mobility for all parameters tested and only slightly reduced with respect to the Langevin limit. In contrast, mobility is not the decisive parameter that determines the nongeminate recombination coefficient, $k_2$, in the latter case, where $k_2$ is a sole function of the morphology, CT and charge-separated (CS) energetics, and CT-state decay properties. Our simulations also show that free charge encounter in the phase-separated disordered blend is determined by the average mobility of all carriers, while CT reformation and resplitting involves mostly states near the transport energy. Therefore, charge encounter is more affected by increased disorder than the resplitting of the CT state. As a consequence, for a given mobility, larger energetic disorder, in combination with a higher hopping rate, is preferred. These findings have implications for the understanding of suppressed recombination in solar cells with nonfullerene acceptors, which are known to exhibit lower energetic disorder than that of fullerenes.

We study a quantum system composed of three interacting qubits, each coupled to a different thermal reservoir. We show how to engineer it to build a quantum device analogous to an electronic bipolar transistor. We outline how the interaction among the qubits plays a crucial role for the appearance of the effect, also linking it to the characteristics of system-bath interactions that govern the decoherence and dissipation mechanisms of the system. By comparison with previous proposals, our model extends the regime of parameters where the transistor effect occurs, the effect being more robust with respect to small variations of the coupling parameters. Moreover, our model appears to be more realistic and directly connected in terms of potential implementations to feasible setups in the domain of quantum spin chains, such as molecular nanomagnets.

When a liquid film lies on a nonwettable substrate, the configuration is unstable, and the film spontaneously ruptures to form droplets. This phenomenon, known as dewetting, commonly leads to undesirable morphological changes. Nevertheless, recent works, combining spontaneous dewetting triggered by thermal annealing and topographic pattern-directed dewetting, demonstrate the possibility of harnessing dewetting with a degree of precision on par with that of advanced lithographic processes for high-performance nanophotonic applications. Since resonant behavior is highly sensitive to geometrical changes, predicting quantitatively dewetting dynamics is of high interest. Here, we develop a continuum model that predicts the evolution of a thin film on a patterned substrate, from the initial reflow to the nucleation and growth of holes. We provide an operative framework based on macroscopic measurements to model the intermolecular interactions at the origin of the dewetting process, involving length scales that span from sub-nanometer to micrometer. A comparison of experimental and simulated results shows that the model can accurately predict the final distributions, thereby offering predictive tools to tailor the optical response of dewetted nanostructures.

Understanding and mitigating loss channels due to two-level systems (TLS) is one of the main cornerstones in the quest of realizing long photon lifetimes in superconducting quantum circuits. Typically, the TLS to which a circuit couples are modeled as a large bath without any coherence. Here we demonstrate that the coherence of TLS has to be considered to accurately describe the ring-down dynamics of a coaxial quarter-wave resonator with an internal quality factor of $0.5\times {10}^9$ at the single-photon level. The transient analysis reveals effective non-Markovian dynamics of the combined TLS and cavity system, which we can accurately fit by introducing a comprehensive TLS model. The fit returns an average coherence time of around $T_2^{\ast }\approx 0.3\mu \mathrm{s}$ for a total of $N\approx {10}^9$ TLS with power-law distributed coupling strengths. Despite the shortly coherent TLS excitations, we observe long-term effects on the cavity decay due to coherent elastic scattering between the resonator field and the TLS. Moreover, this model provides an accurate prediction of the internal quality factor’s temperature dependence.

Metasurfaces that manipulate the reflection of impinging sound have recently received significant attention, but virtually all past designs are passive structures with high temporal and spatial dispersion and thus have narrow bandwidths and are unidirectional. In this work, we introduce a method to design omnidirectional and broadband anomalous acoustic reflectors composed of nonresonant active scatterers arranged in a periodic lattice of subwavelength periodicity. The method relies on the manipulation of the wave-vector component parallel to the reflector’s surface (i.e., transverse component) in a broadband manner and for arbitrary impinging sound directions. To illustrate our method experimentally, we design and measure an anomalous reflecting metasurface operating in free space for which the transverse wave-vector components of the incident and reflected waves differ by a prescribed constant. We show that the effect does not depend on the direction of incidence and has a bandwidth an order of magnitude larger than passive anomalous reflectors. This work shows that the active scatterers behave similarly to the atoms of a natural material rather than the unit cells of gratings or phononic crystals in that rearranging the active scatterers changes the metasurface geometry while preserving the device’s desired functionality.