Superconductivity and charge density waves (CDWs) are competitive, yet coexisting, orders in cuprate superconductors. To understand their microscopic interdependence, a probe capable of discerning ...their interaction on its natural length and time scale is necessary. We use ultrafast resonant soft x-ray scattering to track the transient evolution of CDW correlations in YBa
Cu
O
after the quench of superconductivity by an infrared laser pulse. We observe a nonthermal response of the CDW order characterized by a near doubling of the correlation length within ≈1 picosecond of the superconducting quench. Our results are consistent with a model in which the interaction between superconductivity and CDWs manifests inhomogeneously through disruption of spatial coherence, with superconductivity playing the dominant role in stabilizing CDW topological defects, such as discommensurations.
Constructing bulk graphene materials with well‐reserved 2D properties is essential for device and engineering applications of atomically thick graphene. In this article, the recent progress in the ...fabrications and applications of sterically continuous porous graphene with designable microstructures, chemistries, and properties for energy storage and conversion are reviewed. Both template‐based and template‐free methods have been developed to synthesize the 3D continuously porous graphene, which typically has the microstructure reminiscent of pseudo‐periodic minimal surfaces. The 3D graphene can well preserve the properties of 2D graphene of being highly conductive, surface abundant, and mechanically robust, together with unique 2D electronic behaviors. Additionally, the bicontinuous porosity and large curvature offer new functionalities, such as rapid mass transport, ample open space, mechanical flexibility, and tunable electric/thermal conductivity. Particularly, the 3D curvature provides a new degree of freedom for tailoring the catalysis and transport properties of graphene. The 3D graphene with those extraordinary properties has shown great promises for a wide range of applications, especially for energy conversion and storage. This article overviews the recent advances made in addressing the challenges of developing 3D continuously porous graphene, the benefits and opportunities of the new materials for energy‐related applications, and the remaining challenges that warrant future study.
3D continuously porous graphene formed by folding a single‐sheet graphene into a 3D porous architecture has well‐retained 2D properties of graphene and novel functionalities from 3D structure, representing a distinct class of graphene materials with numerous unique and extraordinary properties. A comprehensive review of 3D continuously porous graphene and their applications in energy conversion and storage is provided.
Topological defects, with an asymmetric local electronic redistribution, are expected to locally tune the intrinsic catalytic activity of carbon materials. However, it is still challenging to ...deliberately create high‐density homogeneous topological defects in carbon networks due to the high formation energy. Toward this end, an efficient NH3 thermal‐treatment strategy is presented for thoroughly removing pyrrolic‐N and pyridinic‐N dopants from N‐enriched porous carbon particles, to create high‐density topological defects. The resultant topological defects are systematically investigated by near‐edge X‐ray absorption fine structure measurements and local density of states analysis, and the defect formation mechanism is revealed by reactive molecular dynamics simulations. Notably, the as‐prepared porous carbon materials possess an enhanced electrocatalytic CO2 reduction performance, yielding a current density of 2.84 mA cm−2 with Faradaic efficiency of 95.2% for CO generation. Such a result is among the best performances reported for metal‐free CO2 reduction electrocatalysts. Density functional theory calculations suggest that the edge pentagonal sites are the dominating active centers with the lowest free energy (ΔG) for CO2 reduction. This work not only presents deep insights for the defect engineering of carbon‐based materials but also improves the understanding of electrocatalytic CO2 reduction on carbon defects.
NH3 thermal treatment on N‐enriched carbon materials is adopted for creating a high density of topological defects by eliminating pyrrolic‐N and pyridinic‐N dopants from carbon materials. It is found that content of pyridinic‐N and pyrrolic‐N in the carbon precursor and the NH3 thermal‐treatment temperature play critical roles in the creation of topological defects during the NH3‐induced removal process, determining the CO2RR performance.
Machine learning active-nematic hydrodynamics Colen, Jonathan; Han, Ming; Zhang, Rui ...
Proceedings of the National Academy of Sciences - PNAS,
03/2021, Letnik:
118, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Hydrodynamic theories effectively describe many-body systems out of equilibrium in terms of a few macroscopic parameters. However, such parameters are difficult to determine from microscopic ...information. Seldom is this challenge more apparent than in active matter, where the hydrodynamic parameters are in fact fields that encode the distribution of energy-injecting microscopic components. Here, we use active nematics to demonstrate that neural networks can map out the spatiotemporal variation of multiple hydrodynamic parameters and forecast the chaotic dynamics of these systems. We analyze biofilament/molecular-motor experiments with microtubule/kinesin and actin/myosin complexes as computer vision problems. Our algorithms can determine how activity and elastic moduli change as a function of space and time, as well as adenosine triphosphate (ATP) or motor concentration. The only input needed is the orientation of the biofilaments and not the coupled velocity field which is harder to access in experiments. We can also forecast the evolution of these chaotic many-body systems solely from image sequences of their past using a combination of autoencoders and recurrent neural networks with residual architecture. In realistic experimental setups for which the initial conditions are not perfectly known, our physics-inspired machine-learning algorithms can surpass deterministic simulations. Our study paves the way for artificial-intelligence characterization and control of coupled chaotic fields in diverse physical and biological systems, even in the absence of knowledge of the underlying dynamics.
Low‐energy density has long been the major limitation to the application of supercapacitors. Introducing topological defects and dopants in carbon‐based electrodes in a supercapacitor improves the ...performance by maximizing the gravimetric capacitance per mass of the electrode. However, the main mechanisms governing this capacitance improvement are still unclear. We fabricated planar electrodes from CVD‐derived single‐layer graphene with deliberately introduced topological defects and nitrogen dopants in controlled concentrations and of known configurations, to estimate the influence of these defects on the electrical double‐layer (EDL) capacitance. Our experimental study and theoretical calculations show that the increase in EDL capacitance due to either the topological defects or the nitrogen dopants has the same origin, yet these two factors improve the EDL capacitance in different ways. Our work provides a better understanding of the correlation between the atomic‐scale structure and the EDL capacitance and presents a new strategy for the development of experimental and theoretical models for understanding the EDL capacitance of carbon electrodes.
Dopants, defects, and double layers: Electrochemical measurements and ab initio calculations on single‐layer CVD‐grown graphene show that topological defects improve the density of states and N‐dopants can tune the Fermi level of graphene, both of which influence the quantum capacitance connected in series with the Helmholtz capacitance and therefore modify the electrical double‐layer (EDL) capacitance.
The idea of employing non-Abelian statistics for error-free quantum computing ignited interest in reports of topological surface superconductivity and Majorana zero modes (MZMs) in FeTe0.55Se0.45. ...However, the topological features and superconducting properties are not observed uniformly across the sample surface. The understanding and practical control of these electronic inhomogeneities present a prominent challenge for potential applications. Here, we combine neutron scattering, scanning angle-resolved photoemission spectroscopy, and microprobe composition and resistivity measurements to characterize the electronic state of Fe1+yTe1−xSex. We establish a phase diagram in which the superconductivity is observed only at sufficiently low Fe concentration, in association with distinct antiferromagnetic correlations, whereas the coexisting topological surface state occurs only at sufficiently high Te concentration. We find that FeTe0.55Se0.45 is located very close to both phase boundaries, which explains the inhomogeneity of superconducting and topological states. Our results demonstrate the compositional control required for use of topological MZMs in practical applications.The compositional dependence of magnetic, superconducting and topological surface states on an iron-based superconductor is reported.
Quantized vortices are key features of quantum fluids such as superfluid helium and Bose—Einstein condensates. The reconnection of quantized vortices and subsequent emission of Kelvin waves along the ...vortices are thought to be central to dissipation in such systems. By visualizing the motion of submicron particles dispersed in superfluid 4 He, we have directly observed the emission of Kelvin waves from quantized vortex reconnection. We characterize one event in detail, using dimensionless similarity coordinates, and compare it with several theories. Finally, we give evidence for other examples of wavelike behavior in our system.
We investigate numerically the motion of active elongated colloidal particles in a nematic liquid crystal. Active particles imposing three different anchoring conditions on the orientation field of ...the solvent are considered: homeotropic, planar, and Janus, which combine both homeotropic and planar conditions at different proportions. Active forces are parallel to the main symmetry axis of the colloidal particles. Our numerical approach sustains topological defects, thermal fluctuations and nematohydrodynamic flow. It is shown that the direction of motion of the active particles is determined by anchoring conditions. Transportation of active colloids with planar (homeotropic) anchoring occurs mainly parallel (perpendicular) to the nematic director field, whereas Janus particles exhibit an intermediate propagation direction. Results apply for active motion at low Reynolds and Ericksen numbers, where distortions on defects surrounding active particles are small.
•Multi-particle Collision Dynamics simulates colloidal particles with different anchoring conditions in nematic liquid crystals.•Anisotropic Janus particles in liquid crystals equilibrate at oblique angles with the nematic director.•Trajectories of active particles in liquid crystals can be tuned by anchoring conditions.
Achieving control and tunability of lyotropic materials has been a long-standing goal of liquid crystal research. Here we show that the elasticity of a liquid crystal system consisting of a dense ...suspension of semiflexible biopolymers can be manipulated over a relatively wide range of elastic moduli. Specifically, thin films of actin filaments are assembled at an oil–water interface. At sufficiently high concentrations, one observes the formation of a nematic phase riddled with ±1/2 topological defects, characteristic of a two-dimensional nematic system. As the average filament length increases, the defect morphology transitions from a U shape into a V shape, indicating the relative increase of the material’s bend over splay modulus. Furthermore, through the sparse addition of rigid microtubule filaments, one can gain additional control over the liquid crystal’s elasticity. We show how the material’s bend constant can be raised linearly as a function of microtubule filament density, and present a simple means to extract absolute values of the elastic moduli from purely optical observations. Finally, we demonstrate that it is possible to predict not only the static structure of the material, including its topological defects, but also the evolution of the system into dynamically arrested states. Despite the nonequilibrium nature of the system, our continuum model, which couples structure and hydrodynamics, is able to capture the annihilation and movement of defects over long time scales. Thus, we have experimentally realized a lyotropic liquid crystal system that can be truly engineered, with tunable mechanical properties, and a theoretical framework to capture its structure, mechanics, and dynamics.
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