Heavy Metal Ion Recovery In article number 2105845, Guiyin Xu, Ju Li, and co-workers prepare a highly porous and functionalized filter with a cyclic π-conjugated backbone and electronic conductivity PAN-S grafted on an industrially produced melamine foam. Selective affinity of Hg2+, Pb2+, Cu2+, and Cd2+ is achieved, and the chemically adsorbed metal ions can be electrochemically desorbed and reduced on counter-electrode, achieving the highest possible waste concentration. This paradigm offers a sustainable and affordable approach for heavy meal ion removal and recovery from wastewater.
Solid-state spin defects, especially nuclear spins with potentially achievable long coherence times, are compelling candidates for quantum memories and sensors. However, their current performances are still limited by dephasing due to variations of their intrinsic quadrupole and hyperfine interactions. We propose an unbalanced echo to overcome this challenge by using a second spin to refocus variations of these interactions while preserving the quantum information stored in the nuclear spin free evolution. The unbalanced echo can be used to probe the temperature and strain distribution in materials. We develop first-principles methods to predict variations of these interactions and reveal their correlation over large temperature and strain ranges. Experiments performed in an ensemble of ∼10^{10} nuclear spins in diamond demonstrate a 20-fold dephasing time increase, limited by other noise sources. We further numerically show that our method can refocus even stronger noise variations than present in our experiments.
In this work, we use Floquet theory to theoretically study the influence of monochromatic circularly and linearly polarized light on the Hofstadter butterfly---induced by a uniform perpendicular magnetic field---for both the kagome and triangular lattices. In the absence of laser light, the butterfly has a fractal structure with inversion symmetry about magnetic flux, $\ensuremath{\phi}=1/4,3/4$, and reflection symmetry about $\ensuremath{\phi}=1/2$. As the system is exposed to an external laser, we find that circularly polarized light deforms the butterfly by breaking the mirror symmetry at flux $\ensuremath{\phi}=1/2$. By contrast, linearly polarized light deforms the original butterfly while preserving the mirror symmetry at flux $\ensuremath{\phi}=1/2$. We find the inversion symmetry is always preserved for both linearly and circularly polarized light. For linearly polarized light, the Hofstadter butterfly depends on the polarization direction. Further, we study the effect of the laser on the Chern number of the lowest band in the off-resonance regime (laser frequency is larger than the bandwidth). For circularly polarized light, we find that low laser intensity will not change the Chern number, but beyond a critical intensity the Chern number will change. For linearly polarized light, the Chern number depends on the polarization direction. Our work highlights the generic features expected for the periodically driven Hofstadter problem on different lattices.
In this work we use Floquet theory to theoretically study the influence of circularly polarized light on disordered two-dimensional models exhibiting topological transitions. We find circularly polarized light can induce a topological transition in extended Kane-Mele models that include additional hopping terms and on-site disorder. The topological transitions are understood from the Floquet-Bloch band structure of the clean system at high symmetry points in the first Brillouin zone. The light modifies the equilibrium band structure of the clean system in such a way that the smallest gap in the Brillouin zone can be shifted from the $M$ points to the $K(K')$ points, the $\Gamma$ point, or even other lower symmetry points. The movement of the minimal gap point through the Brillouin zone as a function of laser parameters is explained in the high frequency regime through the Magnus expansion. In the disordered model, we compute the Bott index to reveal topological phases and transitions. The disorder can induce transitions from topologically non-trivial states to trivial states or vice versa, both examples of Floquet topological Anderson transitions. As a result of the movement of the minimal gap point through the Brillouin zone as a function of laser parameters, the nature of the topological phases and transitions is laser-parameter dependent--a contrasting behavior to the Kane-Mele model.
Spin qubits associated with color centers are promising platforms for various quantum technologies. However, to be deployed in robust quantum devices, the variations of their intrinsic properties with the external conditions, and in particular temperature, should be known with high precision. Unfortunately, a predictive theory on the temperature dependence of the resonance frequency of electron and nuclear spin defects in solids remains lacking. In this work, we develop a first-principles method for the temperature dependence of zero phonon line, zero-field splitting, hyperfine interaction, and nuclear quadrupole interaction of color centers. As a testbed, we compare our ab-initio calculation results with experiments in the Nitrogen-Vacancy (NV) center finding good agreement. Interestingly, we identify the major origin of temperature dependence as a second-order effect of phonon vibration. The method is generally applicable to different color centers and provides a theoretical tool for designing high-precision quantum sensors.
Abstract Mercury, lead, and cadmium are among the most toxic and carcinogenic heavy metal ions (HMIs), posing serious threats to the sustainability of aquatic ecosystems and public health. There is an urgent need to remove these ions from water by a cheap but green process. Traditional methods have insufficient removal efficiency and reusability. Structurally robust, large surface‐area adsorbents functionalized with high‐selectivity affinity to HMIs are attractive filter materials. Here, an adsorbent prepared by vulcanization of polyacrylonitrile (PAN), a nitrogen‐rich polymer, is reported, giving rise to PAN‐S nanoparticles with cyclic π‐conjugated backbone and electronic conductivity. PAN‐S can be coated on ultra‐robust melamine (ML) foam by simple dipping and drying. In agreement with hard/soft acid/base theory, N‐ and S‐containing soft Lewis bases have strong binding to Hg 2+ , Pb 2+ , Cu 2+ , and Cd 2+ , with extraordinary capture efficiency and performance stability. Furthermore, the used filters, when collected and electrochemically biased in a recycling bath, can release the HMIs into the bath and electrodeposit on the counter‐electrode as metallic Hg 0 , Pb 0 , Cu 0 , and Cd 0 , and the PAN‐S@ML filter can then be reused at least 6 times as new. The electronically conductive PAN‐S@ML filter can be fabricated cheaply and holds promise for scale‐up applications.
Abstract Far-field spectral imaging, coupled with computer vision methods, is demonstrated as an effective inspection method for detection, classification, and root-cause analysis of manufacturing defects in large area Si nanopillar arrays. Si nanopillar arrays exhibit a variety of nanophotonic effects, causing them to produce colors and spectral signatures which are highly sensitive to defects, on both the macro- and nanoscales, which can be detected in far-field imaging. Compared with traditional nanometrology approaches like scanning electron microscopy (SEM), atomic force microscopy (AFM), and optical scatterometry, spectral imaging offers much higher throughput due to its large field of view (FOV), micrometer-scale imaging resolution, sensitivity to nm-scale feature geometric variations, and ability to be performed in-line and nondestructively. Thus, spectral imaging is an excellent choice for high-speed defect detection/classification in Si nanopillar arrays and potentially other types of large-area nanostructure arrays (LNAs) fabricated on Si wafers, glass sheets, and roll-to-roll webs. The origins of different types of nano-imprint patterning defects—including particle voids, etch delay, and nonfilling—and the unique ways in which they manifest as optical changes in the completed nanostructure arrays are discussed. With this understanding in mind, computer vision methods are applied to spectral image data to detect and classify various defects in a sample containing wine glass-shaped Si resonator arrays.
When the classical dynamics of a particle in a finite two-dimensional billiard undergoes a transition to chaos, the quantum dynamics of the particle also shows manifestations of chaos in the form of scarring of wave functions and changes in energy level spacing distributions. If we “tile” an infinite plane with such billiards, we find that the Bloch states on the lattice undergo avoided crossings, energy level spacing statistics change from Poisson-like to Wigner-like, and energy sheets of the Brillouin zone begin to “mix” as the classical dynamics of the billiard changes from regular to chaotic behavior.
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