High-Resolution Crystal Truncation Rod Scattering: Application to Ultrathin Layers and Buried Interfaces

In crystalline materials, the presence of surfaces or interfaces gives rise to crystal truncation rods (CTRs) in their X‐ray diffraction patterns. While structural properties related to the bulk of a crystal are contained in the intensity and position of Bragg peaks in X‐ray diffraction, CTRs carry detailed information about the atomic structure at the interface. Developments in synchrotron X‐ray sources, instrumentation, and analysis procedures have made CTR measurements into extremely powerful tools to study atomic reconstructions and relaxations occurring in a wide variety of interfacial systems, with relevance to chemical and electronic functionalities. In this review, an overview of the use of CTRs in the study of atomic structure at interfaces is provided. The basic theory, measurement, and analysis of CTRs are covered and applications from the literature are highlighted. Illustrative examples include studies of complex oxide thin films and multilayers

Disentangling lattice and electronic contributions to the metal–insulator transition from bulk vs. layer confined RNiO₃

In complex oxide materials, changes in electronic properties are often associated with changes in crystal structure, raising the question of the relative roles of the electronic and lattice effects in driving the metal–insulator transition. This paper presents a combined theoretical and experimental analysis of the dependence of the metal–insulator transition of NdNiO3 on crystal structure, specifically comparing properties of bulk materials to 1- and 2-layer samples of NdNiO3 grown between multiple electronically inert NdAlO3 counterlayers in a superlattice. The comparison amplifies and validates a theoretical approach developed in previous papers and disentangles the electronic and lattice contributions, through an independent variation of each. In bulk NdNiO3, the correlations are not strong enough to drive a metal–insulator transition by themselves: A lattice distortion is required. Ultrathin films exhibit 2 additional electronic effects and 1 lattice-related effect. The electronic effects are quantum confinement, leading to dimensional reduction of the electronic Hamiltonian and an increase in electronic bandwidth due to counterlayer-induced bond-angle changes. We find that the confinement effect is much more important. The lattice effect is an increase in stiffness due to the cost of propagation of the lattice disproportionation into the confining material

Engineering crystal structures with light

The crystal structure of a solid largely dictates its electronic, optical and mechanical properties. Indeed, much of the exploration of quantum materials in recent years including the discovery of new phases and phenomena in correlated, topological and two-dimensional materials—has been based on the ability to rationally control crystal structures through materials synthesis, strain engineering or heterostructuring of van der Waals bonded materials. These static approaches, while enormously powerful, are limited by thermodynamic and elastic constraints. An emerging avenue of study has focused on extending such structural control to the dynamical regime by using resonant laser pulses to drive vibrational modes in a crystal. This paradigm of ‘nonlinear phononics’ provides a basis for rationally designing the structure and symmetry of crystals with light, allowing for the manipulation of functional properties at high speed and, in many instances, beyond what may be possible in equilibrium. Here we provide an overview of the developments in this field, discussing the theory, applications and future prospects of optical crystal structure engineering

Posed and spontaneous nonverbal vocalizations of positive emotions: Acoustic analysis and perceptual judgments

When experiencing different positive emotional states, like amusement or relief, we may produce nonverbal vocalizations such as laughs and sighs. In the current study, we describe the acoustic structure of posed and spontaneous nonverbal vocalizations of 14 different positive emotions, and test whether listeners (N =201) map the vocalizations to emotions. The results show that vocalizations of 13 different positive emotions were recognized at better-than-chance levels, but not vocalizations of being moved. Emotions varied in whether vocalizations were better recognized from spontaneous or posed expressions

Posed and spontaneous nonverbal vocalizations of positive emotions: Acoustic analysis and perceptual judgments

When experiencing different positive emotional states, like amusement or relief, we may produce nonverbal vocalizations such as laughs and sighs. In the current study, we describe the acoustic structure of posed and spontaneous nonverbal vocalizations of 14 different positive emotions, and test whether listeners (N =201) map the vocalizations to emotions. The results show that vocalizations of 13 different positive emotions were recognized at better-than-chance levels, but not vocalizations of being moved. Emotions varied in whether vocalizations were better recognized from spontaneous or posed expressions

Magnetic-Field Tuning of Light-Induced Superconductivity in Striped La2−x_{2-x}Bax_xCuO4_4

Optical excitation of stripe-ordered La$_{2-x}$Ba$_x$CuO$_4$ has been shown to transiently enhance superconducting tunneling between the CuO$_2$ planes. This effect was revealed by a blue-shift, or by the appearance of a Josephson Plasma Resonance in the terahertz-frequency optical properties. Here, we show that this photo-induced state can be strengthened by the application of high external magnetic fields oriented along the c-axis. For a 7-Tesla field, we observe up to a ten-fold enhancement in the transient interlayer phase correlation length, accompanied by a two-fold increase in the relaxation time of the photo-induced state. These observations are highly surprising, since static magnetic fields suppress interlayer Josephson tunneling and stabilize stripe order at equilibrium. We interpret our data as an indication that optically-enhanced interlayer coupling in La$_{2-x}$Ba$_x$CuO$_4$ does not originate from a simple optical melting of stripes, as previously hypothesized. Rather, we speculate that the photo-induced state may emerge from activated tunneling between optically-excited stripes in adjacent planes.Comment: 35 pages, 13 figure

Dynamics of photo-induced ferromagnetism in oxides with orbital degeneracy

By using intense coherent electromagnetic radiation, it may be possible to manipulate the properties of quantum materials very quickly, or even induce new and potentially useful phases that are absent in equilibrium. For instance, ultrafast control of magnetic dynamics is crucial for a number of proposed spintronic devices and can also shed light on the possible dynamics of correlated phases out of equilibrium. Inspired by recent experiments on spin-orbital ferromagnet YTiO3 we consider the nonequilibrium dynamics of Heisenberg ferromagnetic insulator with low-lying orbital excitations. We model the dynamics of the magnon excitations in this system following an optical pulse which resonantly excites infrared-active phonon modes. As the phonons ring down they can dynamically couple the orbitals with the low-lying magnons, leading to a dramatically modified effective bath for the magnons. We show this transient coupling can lead to a dynamical acceleration of the magnetization dynamics, which is otherwise bottlenecked by small anisotropy. Exploring the parameter space more we find that the magnon dynamics can also even completely reverse, leading to a negative relaxation rate when the pump is blue-detuned with respect to the orbital bath resonance. We therefore show that by using specially targeted optical pulses, one can exert a much greater degree of control over the magnetization dynamics, allowing one to optically steer magnetic order in this system. We conclude by discussing interesting parallels between the magnetization dynamics we find here and recent experiments on photo-induced superconductivity, where it is similarly observed that depending on the initial pump frequency, an apparent metastable superconducting phase emerges

Human listeners' perception of behavioural context and core affect dimensions in chimpanzee vocalizations

Vocalizations linked to emotional states are partly conserved among phylogenetically related species. This continuity may allow humans to accurately infer affective information from vocalizations produced by chimpanzees. In two pre-registered experiments, we examine human listeners' ability to infer behavioural contexts (e.g. discovering food) and core affect dimensions (arousal and valence) from 155 vocalizations produced by 66 chimpanzees in 10 different positive and negative contexts at high, medium or low arousal levels. In experiment 1, listeners (n = 310), categorized the vocalizations in a forced-choice task with 10 response options, and rated arousal and valence. In experiment 2, participants (n = 3120) matched vocalizations to production contexts using yes/no response options. The results show that listeners were accurate at matching vocalizations of most contexts in addition to inferring arousal and valence. Judgments were more accurate for negative as compared to positive vocalizations. An acoustic analysis demonstrated that, listeners made use of brightness and duration cues, and relied on noisiness in making context judgements, and pitch to infer core affect dimensions. Overall, the results suggest that human listeners can infer affective information from chimpanzee vocalizations beyond core affect, indicating phylogenetic continuity in the mapping of vocalizations to behavioural contexts

Racial/Ethnic Disparities in US Adolescents’ Dietary Quality and Its Modification by Weight-Related Factors and Physical Activity

There are well-known disparities in the prevalence of obesity across racial-ethnic groups, although the behavioral and psychological factors driving these disparities are less well understood. Therefore, the objectives of this study were: (1) to examine differences in dietary quality by race/ethnicity and weight-related variables [body mass index (BMI), weight loss attempt, and weight dissatisfaction] and physical activity (PA) using the Health Eating Index-2015 (HEI-2015); and (2) to investigate the interactions and independent associations of race/ethnicity, weight-related variables and PA on dietary quality. Data for adolescents aged 12–19 years (n = 3373) were abstracted from the 2007–2014 National Health and Nutrition and Examination Survey and analyzed using multiple PROC SURVEYREG, adjusting for demographics and accounting for complex sampling. Analyses determined that Hispanic males had better overall HEI-2015 scores than non-Hispanic whites (48.4 ± 0.5 vs. 45.7 ± 0.6, p = 0.003) or blacks (48.4 ± 0.5 vs. 45.5 ± 0.5, p \u3c 0.001). Hispanic females also had better dietary quality than non-Hispanic whites (50.2 ± 0.4 vs. 47.5 ± 0.5, p \u3c 0.001) and blacks (50.2 ± 0.4 vs. 47.1 ± 0.5, p \u3c 0.001). Meeting the PA recommendation modified racial/ethnic differences in dietary quality for females (p = 0.011) and this was primarily driven by the associations among non-Hispanic white females (ΔR2 = 2.6%, p = 0.0004). The study identified racial/ethnic and gender differences among adolescents in factors that may promote obesity. Results may be useful for obesity prevention efforts designed to reduce health disparities in adolescents

Optical Stabilization of Fluctuating High Temperature Ferromagnetism in YTiO₃

In quantum materials, degeneracies and frustrated interactions can have a profound impact on the emergence of long-range order, often driving strong fluctuations that suppress functionally relevant electronic or magnetic phases. Engineering the atomic structure in the bulk or at heterointerfaces has been an important research strategy to lift these degeneracies, but these equilibrium methods are limited by thermodynamic, elastic, and chemical constraints. Here, we show that all-optical, mode-selective manipulation of the crystal lattice can be used to enhance and stabilize high-temperature ferromagnetism in YTiO3, a material that exhibits only partial orbital polarization, an unsaturated low-temperature magnetic moment, and a suppressed Curie temperature, Tc = 27 K. The enhancement is largest when exciting a 9 THz oxygen rotation mode, for which complete magnetic saturation is achieved at low temperatures and transient ferromagnetism is realized up to Tneq> 80 K, nearly three times the thermodynamic transition temperature. First-principles and model calculations of the nonlinear phonon-orbital-spin coupling reveal that these effects originate from dynamical changes to the orbital polarization and the makeup of the lowest quasi-degenerate Ti t2g levels. Notably, light-induced high temperature ferromagnetism in YTiO3 is found to be metastable over many nanoseconds, underscoring the ability to dynamically engineer practically useful non-equilibrium functionalities