Emergent Modes Research Articles

Emergent coherent modes in nonlinear magnonic waveguides detected at ultrahigh frequency resolution

Nonlinearity of dynamic systems plays a key role in neuromorphic computing, which is expected to reduce the ever-increasing power consumption of machine learning and artificial intelligence applications. For spin waves (magnons), nonlinearity combined with phase coherence is the basis of phenomena like Bose–Einstein condensation, frequency combs, and pattern recognition in neuromorphic computing. Yet, the broadband electrical detection of these phenomena with high-frequency resolution remains a challenge. Here, we demonstrate the generation and detection of phase-coherent nonlinear magnons in an all-electrical GHz probe station based on coplanar waveguides connected to a vector network analyzer which we operate in a frequency-offset mode. Making use of an unprecedented frequency resolution, we resolve the nonlocal emergence of a fine structure of propagating nonlinear magnons, which sensitively depends on both power and a magnetic field. These magnons are shown to maintain coherency with the microwave source while propagating over macroscopic distances. We propose a multi-band four-magnon scattering scheme that is in agreement with the field-dependent characteristics of coherent nonlocal signals in the nonlinear excitation regime. Our findings are key to enable the seamless integration of nonlinear magnon processes into high-speed microwave electronics and to advance phase-encoded information processing in magnonic neuronal networks.

Emergence and evolution of electronic modes with temperature in spin-gapped Mott and Kondo insulators

Electronic modes emerge within the band gap at nonzero temperature in strongly correlated insulators such as Mott and Kondo insulators, exhibiting momentum-shifted magnetic dispersion relations from the band edges. As the temperature increases, the emergent modes gain considerable spectral weights and form robust bands that differ from the zero-temperature bands. Here, the origin of the emergent modes, their relation to doping-induced modes, and how their spectral weights increase with temperature are clarified in the ladder and bilayer Hubbard models and one- and two-dimensional Kondo lattice models using effective theory for weak inter-unit-cell hopping and numerical calculations. The results indicate that the temperature-driven change in the band structure reflecting spin excitation, including the change in the number of bands, can be observed in various strongly correlated insulators even with a spin gap, provided that the temperature increases up to about spin-excitation energies. The controlled analyses developed in this study significantly contribute to the fundamental understanding of the band structure of strongly correlated insulators at nonzero temperature. Published by the American Physical Society 2024

‘Who knows what will come next to interrupt our assessments’: the adaptability of assessments across face-to-face and online instructional environments

Universities are increasingly facing disruptions from political crises, natural disasters and public health emergencies, prompting a shift to emergency online teaching. It is different to normal online teaching as students may lose access to campus, community/society or even hosting countries. This qualitative study investigated the adaptability of assessments when shifting entirely from face-to-face to emergent online modes. Data was collected from four disciplines at the macro level and 74 courses from eight disciplines at the micro level. Five design feature dimensions were identified as affecting assessment adaptability between two instructional environments: students’ resources access, student autonomy, measurement focus, external standard adherence and venues/contexts/equipment reliance. The results revealed an increasing use of asynchronous assessments and increased student control and responsibility in assessments. Three levels of changes were observed, including pedagogical changes from testing students’ memories to measuring students’ higher-level understanding. In addition to the challenges in assessment security reported in previous literature about shifts to online modes, this study identified new areas of challenges to assessment validity, fairness of assessments, teacher control, teachers’ and students’ assessment literacy and university infrastructure. A model on the adaptability of assessment is proposed, offering implications for online assessment.

Ground Subsidence, Driving Factors, and Risk Assessment of the Photovoltaic Power Generation and Greenhouse Planting (PPG&GP) Projects in Coal-Mining Areas of Xintai City Observed from a Multi-Temporal InSAR Perspective

In recent years, photovoltaic power generation and greenhouse planting (PPG&GP) have become effective approaches for reconstructing and restoring the ecological environment of old coal-mining industry bases, such as Xintai City. However, the ecological impacts or improvements of the PPG&GP projects and their daily operations on the local environment are still unclear. To solve these problems, this study retrieved the ground deformation velocities and time series of the study region by performing the Small-Baseline Subset (SBAS)-Interferometric Synthetic Aperture Radar (InSAR) technique on the Advanced Land Observing Satellite (ALOS) PALSAR and Sentinel-1 SAR datasets. With these deformation results, the spatial analysis indicated that the area of the subsidence region within the PPG&GP projects reached 10.70 km2, with a magnitude of approximately −21.61 ± 12.10 mm/yr. Also, even though the ground deformations and their temporal changes were both visible in the construction and operation stages of the PPG&GP projects, the temporal analysis demonstrated that most observation points finally entered into the stationary phases in the late stage of the observation period. This phenomenon validated the effectiveness of the PPG&GP projects in enhancing the ground surface stability in coal-mining areas. Additionally, the precipitation, geological structure, increased coal-mining depths, and emergent agricultural modes were assumed to be the major impact factors controlling the ground deformation within the local PPG&GP projects. Finally, a novel risk assessment method with a designed index of IRA was utilized to classify the ground subsidence risks of the PPG&GP projects into three levels: Low (69.7%), Medium (16.9%), and High (9.4%). This study sheds a bright light on the ecological monitoring and risk management of the burgeoning industrial and agricultural infrastructures, such as the PPG&GP projects, constructed upon the traditional coal-mining areas in China from a multi-temporal InSAR perspective.

Evidence for Trans-Oligoene Chain Formation in Graphene Induced by Iodine.

Functionalization of pristine graphene by hydrogen and fluorine is well studied, resulting in graphane and fluorographene structures. In contrast, functionalization of pristine graphene with iodine has not been reported. Here, the functionalization of graphene with iodine using photochemical activation is presented, which is thermally reversible at 400°C. Additional dispersive dominant Raman modes that are probed by resonance Raman spectroscopy are observed. Additionally, iodinated graphene is probed by Kelvin probe force microscopy and by transport measurements showing p-doping surpassing non-covalent iodine doping by charge transfer-complex formation. The emergent Raman modes combined with strong p-doping indicate that iodine functionalization is distinct from simple iodine doping. A reaction mechanism based on these findings is proposed, identifying the large size of iodine atoms as the probable cause governing regiochemically controlled addition due to steric hinderance of reactive sites. The modification of the electronic structure is explained by the confinement of 1D trans-oligoene chains between sp3-defects. These results demonstrate the uniqueness of iodine reactivity toward graphene and the modification of the electronic structure of iodinated graphene, highlighting its dependence on the spatial arrangement of substituents.

Phonon promoted charge density wave in topological kagome metal ScV6Sn6

Charge density wave (CDW) orders in vanadium-based kagome metals have recently received tremendous attention, yet their origin remains a topic of debate. The discovery of ScV6Sn6, a bilayer kagome metal featuring an intriguing 3×3×3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{3}\ imes\\sqrt{3}\ imes3$$\\end{document} CDW order, offers a novel platform to explore the underlying mechanism behind the unconventional CDW. Here, we combine high-resolution angle-resolved photoemission spectroscopy, Raman scattering and density functional theory to investigate the electronic structure and phonon modes of ScV6Sn6. We identify topologically nontrivial surface states and multiple van Hove singularities (VHSs) in the vicinity of the Fermi level, with one VHS aligning with the in-plane component of the CDW vector near the K¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\bar{K}$$\\end{document} point. Additionally, Raman measurements indicate a strong electron-phonon coupling, as evidenced by a two-phonon mode and new emergent modes. Our findings highlight the fundamental role of lattice degrees of freedom in promoting the CDW in ScV6Sn6.

Flow-Inflated Selective Sampling for Efficient Agent-Based Dynamic Ride-Pooling Simulations

Agent-based simulations are powerful tools for simulating emergent mobility modes, but they often require significant memory and computing power. To address this issue, researchers have previously used sampling techniques, where only a fraction of agents are explicitly simulated while others are simulated through teleportation. However, recent studies have highlighted the challenges of scaling ride-pooling simulations because of their reliance on demand density, which does not scale linearly. In this study, we introduce a new methodology for simulating dynamic ride-pooling services called flow-inflated selective sampling (FISS). Unlike previous approaches, FISS considers all agents but—for selected modes—only explicitly simulates a fraction of their trips while simulating the remaining trips through teleportation. Here, we explicitly simulate all public transport and ride-pooling trips and sample private car trips. The capacity consumption of explicitly simulated cars is scaled up to obtain realistic traffic flows, rather than adjusting the network capacity as in previous approaches. We implement FISS in the MATSim simulation environment for a large scenario in Munich, Germany, and show that it preserves traffic flows while keeping key performance indicators of ride-pooling services stable and unbiased. Mode choice decisions based on FISS also remain stable, and runtimes of the assignment can be almost halved. Overall, FISS is a simple yet effective approach that can significantly reduce the computational burden of agent-based simulations while maintaining the accuracy of the results. It can be particularly useful for simulating ride-pooling services, which can be challenging to scale because of their dependence on demand density.

Bridging Structure, Magnetism, and Disorder in Iron-Intercalated Niobium Diselenide, FexNbSe2, below x = 0.25.

Transition-metal dichalcogenides (TMDs) intercalated with magnetic ions serve as a promising materials platform for developing next-generation, spin-based electronic technologies. In these materials, one can access a rich magnetic phase space depending on the choice of intercalant, host lattice, and relative stoichiometry. The distribution of these intercalant ions across given crystals, however, is less well defined-particularly away from ideal packing stoichiometries-and a convenient probe to assess potential longer-range ordering of intercalants is lacking. Here, we demonstrate that confocal Raman spectroscopy is a powerful tool for mapping the onset of intercalant superlattice formation in Fe-intercalated NbSe2 (FexNbSe2) for 0.14 ≤ x < 0.25. We use single-crystal X-ray diffraction to confirm the presence of longer-range intercalant superstructure and employ polarization-, temperature-, and magnetic field-dependent Raman measurements to examine both the symmetry of emergent phonon modes in the intercalated material and potential magnetoelastic coupling. Magnetometry measurements further indicate a correlation between the onset of magnetic ordering and the relative degree of intercalant superlattice formation. These results show Raman spectroscopy to be an expedient, local probe for mapping intercalant ordering in this class of magnetic materials.

Greening energy governance through agencification in the Global South: Drivers and implications

AbstractThis article offers the first comprehensive analysis of the emergent modes for greening electricity governance through agencification in the Global South by examining the drivers and role of renewable energy agencies (REAs) in various countries in the Middle East and North Africa region. Furthermore, the article illustrates the impact of this form of agencification on the deployment of renewables and the “democratization” of energy governance. We found that the diffusion of REAs is facilitated by the intermediation of international and transnational actors, whereas their role in national energy governance is constrained by the fossil fuels rentier political economy. As an institutional strategy for greening energy governance, agencification has the potential to foster the deployment of renewables: agencies can catalyze external funding overcoming regulatory and policy barriers. However, this strategy can reproduce top‐down approaches to policymaking, hindering the “democratic” potentials of the energy transition.

Emergent Edge Modes in Shifted Quasi-One-Dimensional Charge Density Waves.

We propose and study a two-dimensional phase of shifted charge density waves (CDW), which is constructed from an array of weakly coupled 1D CDW wires whose phases shift from one wire to the next. We show that the fully gapped bulk CDW has topological properties, characterized by a nonzero Chern number, that imply edge modes within the bulk gap. Remarkably, these edge modes exhibit spectral pseudoflow as a function of position along the edge, and are thus dual to the chiral edge modes of Chern insulators with their spectral flow in momentum space. Furthermore, we show that the CDW edge modes are stable against interwire coupling. Our predictions can be tested experimentally in quasi-1D CDW compounds such as Ta_{2}Se_{8}I.

Governing Queer Histories and Futures: A Critical Place-Based Analysis of State Apology

The southern island of Tasmania is renowned for being the last Australian state to decriminalise homosexuality in 1997. Twenty years after the repeal of these laws, the state parliament of Tasmania passed legislation introducing an expungement scheme for historical homosexual convictions and delivered an apology for their harms. In this article, we draw upon theories of sexual citizenship to develop a critical place-based analysis of the Tasmanian apology that is attentive to the specificities of the region’s political, social, and cultural context. We argue that the parliament’s attempts to redefine the boundaries of sexual belonging through apology and expungement entail new forms of erasure, exclusion and policing. The limits of the apology’s liberal discourse of progress are foretold by several tendencies within its narration, including: the persistent impulse to erase both past records of the law’s violence and future LGBTQIA + identities; assumptions of sexual essentialism and biological determinism; and the uneasy demarcation of il/legal sexual practices, which reasserts the state’s authority to govern sexuality through recourse to the criminal law. Our analysis highlights the need for more place-based analysis of emergent modes of sexual governance within queer criminology and for further research into the material benefits, if any, that apologies and expungement schemes provide to those affected.

Edge reconstruction and emergent neutral modes in integer and fractional quantum Hall phases

This paper comprises a review of our recent works on fractional chiral modes that emerge due to edge reconstruction in integer and fractional quantum Hall (QH) phases. The new part added is an analysis of edge reconstruction of the ν = 2/5 phase. QH states are topological phases of matter featuring chiral gapless modes at the edge. These edge modes may propagate downstream or upstream and may support either charge or charge-neutral excitations. From topological considerations, particle-like QH states are expected to support only downstream charge modes. However the interplay between the electronic repulsion and the boundary confining potential may drive certain quantum phase transitions (called reconstructions) at the edge, which are associated to the nucleation of additional pairs of counter-propagating modes. Employing variational methods, here we study edge reconstruction in the prototypical particle-like phases at ν = 1, 1/3, and 2/5 as a function of the slope of the confining potential. Our analysis shows that subsequent renormalization of the edge modes, driven by disorder-induced tunnelling and intermode interactions, may lead to the emergence of upstream neutral modes. These predictions may be tested in suitably designed transport experiments. Our results are also consistent with previous observations of upstream neutral modes in these QH phases and could explain the absence of anyonic interference in electronic Mach-Zehnder setups.

Climate governance at the fringes: Peri-urban flooding drivers and responses

There is a large body of scientific evidence on the climate crisis and flooding in urban areas. Extreme weather events are producing extensive property damage and loss of life and require new modes of flood governance. However, the climate crisis does not stop at the city limits: peri-urban areas have related but distinct flood challenges due to land use change, regulation, perceptions, and capacity to develop collective responses. The aim of the literature review is to synthesize peri-urban flood governance drivers and responses with a particular emphasis on empirical findings from the past decade. The literature review draws on findings from 26 empirical case studies with respect to how and where research is conducted on peri-urban flood governance, the drivers of peri-urban flooding, and the responses by peri-urban stakeholders to address flood risks. A common governance approach involves autonomous adaptation that results in maladaptation – both of which are critiqued as inadequate to address flood risks. The findings reveal a host of specific peri-urban challenges in addressing flooding but also point towards opportunities for new modes of adaptive governance. The article concludes by reflecting on the promise of developing an adaptive governance approach to peri-urban flooding to acknowledge the social and ecological complexities of climate change while opening up possibilities for emergent modes and innovative approaches of collaborative problem-solving.

Magnetoelastic Sensor Optimization for Improving Mass Monitoring.

Magnetoelastic sensors, typically made of magnetostrictive and magnetically-soft materials, can be fabricated from commercially available materials into a variety of shapes and sizes for their intended applications. Since these sensors are wirelessly interrogated via magnetic fields, they are good candidates for use in both research and industry, where detection of environmental parameters in closed and controlled systems is necessary. Common applications for these sensors include the investigation of physical, chemical, and biological parameters based on changes in mass loading at the sensor surface which affect the sensor’s behavior at resonance. To improve the performance of these sensors, optimization of sensor geometry, size, and detection conditions are critical to increasing their mass sensitivity and detectible range. This work focuses on investigating how the geometry of the sensor influences its resonance spectrum, including the sensor’s shape, size, and aspect ratio. In addition to these factors, heterogeneity in resonance magnitude was mapped for the sensor surface and the effect of the magnetic bias field strength on the resonance spectrum was investigated. Analysis of the results indicates that the shape of the sensor has a strong influence on the emergent resonant modes. Reducing the size of the sensor decreased the sensor’s magnitude of resonance. The aspect ratio of the sensor, along with the bias field strength, was also observed to affect the magnitude of the signal; over or under biasing and aspect ratio extremes were observed to decrease the magnitude of resonance, indicating that these parameters can be optimized for a given shape and size of magnetoelastic sensor.

Chiral valley phonons and flat phonon bands in moiré materials

We investigate the chirality of phonon modes in twisted bilayer WSe2 and demonstrate distinct chiral behavior of the $K/K^\prime$ valley phonons for twist angles close to $0^{\circ}$ and close to $60^{\circ}$. In particular, multiple chiral non-degenerate $K/K^\prime$ valley phonons are found for twist angles near $60^{\circ}$ whereas no non-degenerate chiral modes are found for twist angles close to $0^\circ$. Moreover, we discover two sets of emergent chiral valley modes that originate from an inversion symmetry breaking at the moir\'{e} scale and find similar modes in moir\'{e} patterns of strain-engineered bilayers WSe2 and MoSe2/WSe2 heterostructures. At the energy gap between acoustic and optical modes, the formation of flat phonon bands for a broad range of twist angles is observed in the twisted bilayer WSe2. Our findings are relevant for understanding electron-phonon and exciton-phonon scattering in moir\'e materials and also for the design of phononic analogues of flat band electrons.

After Disasters

This article explores the COVID-19 pandemic to extend the temporal horizon of (post-)disaster mobilities research. We are not only interested in the conspicuous disruption to mobilities wrought by disasters, nor the emergent modes of movement constituted in disasters’ immediate aftermaths. Rather, with special reference to Nepal, this article attends to the jagged and protracted process of remobilizing the world in the wake of dramatic events like COVID-19. In short, we are concerned here with the uneven politics of “getting back to normal.” Two dimensions of this are discussed via a critical reflection on the widespread “dimmer switch” metaphor of remobilization: (1) the uneven rhythms and refractions of remobilization, and (2) the hegemony of “normal” mobilities systems. Using “light” as an illuminating analytic, we renew calls to examine the disparate impacts of disasters themselves, and also to analyze the uneven politics of “getting back” to “normal” mobilities after disasters.

Higher-order topology and corner triplon excitations in two-dimensional quantum spin-dimer models

The concept of free fermion topology has been generalized to $d$-dimensional phases that exhibit $(d-n)$-dimensional boundary modes, such as zero-dimensional (0D) corner excitations. Motivated by recent extensions of these ideas to magnetic systems, we consider 2D quantum paramagnets formed by interacting spin dimers with dispersive triplet excitations. We propose two examples of such dimer models, where the spin-gapped bosonic triplon excitations are shown to host bands with nontrivial higher-order topology. We demonstrate this using real-space Bogoliubov--de Gennes calculations that reveal the existence of mid-bandgap corner triplon modes as a signature of higher-order bulk topology. We provide an understanding of the higher-order topology in these systems via a computation of bulk topological invariants as well as the construction of edge theories, and study their phase transitions as we tune parameters in the model Hamiltonians. We also discuss possible experimental approaches for detecting the emergent corner triplon modes.

Grand challenges and emergent modes of convergence science

To address complex problems, scholars are increasingly faced with challenges of integrating diverse domains. We analyzed the evolution of this convergence paradigm in the ecosystem of brain science, a research frontier that provides a contemporary testbed for evaluating two modes of cross-domain integration: (a) cross-disciplinary collaboration among experts from academic departments associated with disparate disciplines; and (b) cross-topic knowledge recombination across distinct subject areas. We show that research involving both modes features a 16% citation premium relative to a mono-domain baseline. We further show that the cross-disciplinary mode is essential for integrating across large epistemic distances. Yet we find research utilizing cross-topic exploration alone—a convergence shortcut—to be growing in prevalence at roughly 3% per year, significantly outpacing the more essential cross-disciplinary convergence mode. By measuring shifts in the prevalence and impact of different convergence modes in the 5-year intervals up to and after 2013, we find that shortcut patterns may relate to competitive pressures associated with Human Brain funding initiatives launched that year. Without policy adjustments, flagship funding programs may unintentionally incentivize suboptimal integration patterns, thereby undercutting convergence science’s potential in tackling grand challenges.

Sago Versus Rice and the Reorganisation of Ritual Spacetime: Competing Modes of Dependency in an Age of Decentralisation in Asmat, Indonesian Papua

ABSTRACTAsmat social worlds are permeated with multiple forms of dependency. In this paper, I ask how different modalities of dependency inter‐relate within the space and time of Asmat life, and how this is being reshaped by Asmat's increasing incorporation within broader structural orders during a period of national decentralisation. First, I describe how relations of dependency shape everyday life, through a discussion of the time and space of quotidian food distribution and concomitant claim‐making. Then, I outline how forms of inter‐clan interdependency innovate on the above pattern during ritual feasting, which generates remarkable social co‐presence through ritualised interdependent work. Finally, I explore how feasting interdependence, and its organisation in space and time, is being warped by ‘The Allocation of Village Funds’ (‘Alokasi Dana Desa’), a decentralised government grant. I do so via a case study of a ritual feast house construction project, in which Asmat villagers attempted to reckon with new forms of dependency typified, in indigenous discourse, by the distinction between ‘sago’ and ‘rice’ as local versus introduced staple foods associated with contrasting regimes of action. At stake here, in the collision between indigenous and newly emergent modes of dependency, is the viability of socially valuable modes of ritual life, which, in an age of decentralisation, are becoming shaped by and reliant on new types of forces outside of the community's own labour and control.

Between vulnerability and resistance: How a woman copes with dramatic implications of COVID-19 in Russia.

During the summer of 2020, a woman in Russia not only contracted COVID‐19 herself but also lost her husband to virus‐related health complications and, later, lost her job. This article is based on interviews with her about vulnerability and ways of coping with the pandemic’s effects as the sole caregiver and breadwinner for her 4‐year‐old child. Her ways of dealing with this chain of severe, life‐changing events inspired us to analyze her case through Judith Butler’s feminist lens of vulnerability, conceptualized as the very source of resistance. The results of the analysis illustrate vulnerability and emergent modes of resistance as gendered responsibilities of giving and receiving care, as well as the power of solidarity. Furthermore, the study shows how the political, social, and economic context of Russia shapes gendered experiences of vulnerability and possibilities for resistance.