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Electron-nuclear spin interactions by pulsed optical pumping have been found to polarize the nuclear spin system, leading to the nuclei building up an intrinsic magnetic field known as the Overhauser field. Studies have indicated an Overhauser field hysteresis effect dependent on the sweep direction of an externally applied magnetic field in negatively detuned periodically pumped Si-doped GaAs. Although predictions of bistable mode-locked electron spin precession frequency modes have been made for systems exhibiting this hysteresis, there have been no reports on the experimental observation of said bistable spin precession modes. This report details the evolution of bistable Overhauser field solutions leading to a hysteretic effect in negatively detuned optical excitation of Si-doped GaAs by magneto-optic pump–probe spectroscopy in the Voigt geometry and investigates the resulting consequence of this hysteresis acting on the electron spin system. One manifestation of the Overhauser field hysteresis acting on the electron spin system leads to the discretization of bistable mode-locked electron spin precession modes within a given band of externally applied magnetic fields. A method for preferentially accessing the two different and stable mode-locked spin precession modes within a given band of externally applied magnetic field is outlined, which may be of interest for communities utilizing electron and nuclear spins for information processing protocols. [ABSTRACT FROM AUTHOR]

Large magnetocaloric effects can be observed in materials with first-order magneto-structural phase transition. However, materials with large thermal hysteresis show a reduced effect in moderate fields (∼ 2 T) because the external field is insufficient to induce a fully reversible transformation. The hysteresis can be overcome or even exploited by applying a second external stimulus. A multi-stimuli test bench has been built to demonstrate the multicaloric effect in FeRh alloy using a pulsed magnetic field up to 9 T and a uniaxial stress of up to 700 MPa. A cyclic multicaloric effect of ± 2.5 K could be observed for a sequential application of a pulsed field of 3 T and a uniaxial stress of 700 MPa. The interplay among external field strength, thermal hysteresis, and the transition width enables the use of pulsed magnetic fields and allows a decoupling of the applied magnetic field and the heat transfer process in the multi-stimuli cycle. [ABSTRACT FROM AUTHOR]

Variations from equilibrium Young's angle, known as contact angle hysteresis (CAH), are frequently observed upon droplet deposition on a solid surface. This ubiquitous phenomenon indicates the presence of multiple local surface energy minima for the sessile droplet. Previous research primarily explains CAH via considering macroscopic roughness, such as topographical defects, which alter the effective interfacial energy between the fluid phase and the solid phase, thereby shifting the global surface energy minimum. One typical example is the classic Cassie–Baxter–Wenzel theory. Here, we propose an alternative microscopic mechanism that emphasizes the complexity of molecular rearrangements at the fluid–solid interface, treating their interfacial tensions as variables, which results in multiple local surface energy minima. Our theoretical framework demonstrates that CAH can occur even on chemically homogeneous and mechanically smooth-flat substrates, aligning with previously unexplained experimental observations. In addition, we explore the interplay between macroscopic and microscopic roughness in influencing CAH and clarify the contrasting wetting behaviors—the lotus effect and the rose petal effect—on hierarchical roughness from a thermodynamic perspective. This work provides valuable insights into surface tension determination by restoring the natural physical properties of interfaces and illuminates the multifaceted mechanisms underlying the everyday occurrences of CAH. [ABSTRACT FROM AUTHOR]

Structural disorder in mesoporous solids gives rise to complex phase behavior for materials confined within their pore spaces. As a result, a wide spectrum of possible phase configurations associated with spatial distributions of thermodynamic phases throughout the pore networks can be realized in experiments. Despite their importance, quantifying these states remains largely unaddressed. By considering solid–liquid equilibria as a representative example and using a simple random network model, we investigate the spectrum of such states accessible in real experiments and relate this spectrum to the structural characteristics of porous solids. We classify these states by their free energies and demonstrate how network effects break degeneracies for specific phase compositions and temperatures. Furthermore, we identify the experimental conditions that delineate boundary free energy states, differentiating accessible from inaccessible states. The insights from this study on solid–liquid equilibria are also equally applicable to gas–liquid equilibria in confined spaces and contribute to a deeper understanding of relaxation dynamics associated with hysteresis. [ABSTRACT FROM AUTHOR]

Marine foundation species are critical for the structure and functioning of ecosystems and constitute the pillar of trophic chains while also providing a variety of ecosystem services. In recent decades, many foundation species have declined in abundance, sometimes threatening their current geographical distribution. Kelps (Laminariales) are the primary foundation species in temperate coastal systems worldwide. Kelp ecosystems are notoriously variable, challenging the identification of key factors controlling their dynamics. Identification of these drivers is key to predicting the fate of kelp ecosystems under climatic change and to informing management and conservation decisions such as restoration. Here, we used in situ data from long-term monitoring programs across 1350 km of coast spanning multiple biogeographic regions in the state of California (USA) to identify the major regional drivers of density of two dominant canopy-forming kelp species and to elucidate the spatial and temporal scales over which they operate. We used generalized additive mixed models to identify the key drivers of density of two dominant kelp species (Nereocystis luetkeana and Macrocystis pyrifera) across four ecological regions of the state of California (north, central, southwest, and southeast) and for the past two decades (2004-2021). The dominant drivers of kelp density varied among regions and species but always included some combination of nitrate availability, wave energy and exposure, density of purple sea urchins, and temperature as the most important predictors. These variables explained 63% of the variability of bull kelp in the northern and central regions, and 45% and 51.4% of the variability in giant kelp for the central/southwest and southeast regions, respectively. These large-scale analyses infer that a combination of lower nutrient availability, changes in wave energy and exposure, and increases in temperature and purple sea urchin counts have contributed to the decline of kelp observed in the last decade. Understanding the drivers of kelp dynamics can be used to identify regional patterns of historical stability and periods of significant change, ultimately informing resource management and conservation decisions such as site selection for kelp protection and restoration.

The generation of above-bandgap photovoltage, referred to as the anomalous photovoltaic effect (APV), is an extraordinary characteristic sought after property in bulk ferroelectric photovoltaic devices. Despite the fact that the relatively narrow bandgap of BiFeO3 (BFO) (2.7 eV) induces a comparatively larger generation of photocurrent than other ferroelectric photovoltaic, it falls short in producing an anomalous photovoltage (Eg ≪ Voc) and exhibits leaky ferroelectric hysteresis due to unavoidable oxygen vacancies. This work revealed a reduction in oxygen vacancies through the substitution of Ba(Fe1/2Nb1/2)O3 in BFO, leading to improved structural, morphological, synchrotron XPS, and electrical properties. This reduction in oxygen vacancies has resulted in an impressive above-bandgap photovoltage (APV) of 4.41 V for 80BFO–20BFN with greater ferroelectric polarization (Pr = 20.45 μC/cm2) observed at the co-existence of polar and non-polar phases. Moreover, both theoretical and experimental optical analyses have demonstrated a significant decrease in the bandgap to 1.92 eV, effectively extending the visible region close to 653 nm. As a result, a larger population of photoexcited charge carriers is generated, enabling the attainment of a high current density (Jsc) of 0.75 μA/cm2 under 100 mW/cm2 light irradiation. [ABSTRACT FROM AUTHOR]