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-derived materials
摘要： Symmetry and dimensionality are essential factors defining lattice dynamics and conductivity (κ). Here, we critically examine these via ab initio Boltzmann transport applied to single chain and bulk electride Ba3N and Ba3NX (X = Sb,Bi). Chiral phonons in one-dimensional chains obey new symmetry-based scattering rules that limit thermal resistance. Weak chain coupling breaks these in the bulk, giving lower κ and large κ anisotropy. Curiously, intercalation of large X atoms binds chains more strongly, reducing the volume, yet gives lower κ and transforms the electronic behavior. Insights developed here can be more generally applied to other materials and provide avenues for predictive materials design.
关键词： symmetry,lattice dynamics,Ba3NX,dimensionality,thermal conductivity,Ba3N,chiral phonons,electride
更新于2025-09-09 09:28:46
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Wavefront reconstruction of vortex beams via a simplified transport of intensity equation and its symmetry based error reduction
摘要： We present an unexplored non-interferometric approach for wavefront measurement of vortex beams based on the transport of intensity equation. By exploiting the symmetries of vortexes we are able to simplify the transport of intensity equation to a reduced expression not reported before in the context of phase imaging. This reduced model can be solved to measure the phase profile of vortexes via one-dimensional operations only without the complexities pertaining the regular transport of intensity equation. We also use the axial symmetry exhibited by the intensity profile of vortexes to build a noise filtering scheme exclusive to circularly symmetric images and thus address electronic noise in digital imaging systems. We present a series of numerical experiments both to clarify how to apply our proposal step by step and to prove its overall functionality.
关键词： optics,free-space,orbital angular momentum,noisy data,axial symmetry,quantitative phase imaging,non-interferometric techniques,optical vortex
更新于2025-09-09 09:28:46
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Transient Glass Formation around a Quadrupolar Photoexcited Dye in a Strongly H-Bonding Liquid Observed by Transient 2D-IR Spectroscopy
摘要： A photoexcited quadrupolar dye is directly observed using transient 2D-IR spectroscopy. Upon solvent-induced symmetry breaking, the H-bond accepting abilities of the two nitrile end-groups change drastically, and in extreme protic (‘superprotic’) solvents, a tight H-bond complex forms at one end. The time evolution of the 2D C≡N lineshape in methanol points to rapid, 2-3 ps, spectral diffusion due to fluctuations of the H-bonding network. Similar behaviour is observed in a superprotic solvent shortly after photoexcitation of the dye. However, at later time, the completely inhomogeneous band does not exhibit spectral diffusion for at least 5 ps, pointing to a glass-like environment around one side of the dye. About half of the excited dyes show this behaviour attributed to the tight H-bond complex, whereas the others are loosely bound. A weak cross peak these excited state sub- indicates partial exchange between populations.
关键词： charge transfer,symmetry breaking,ultrafast spectroscopy,Hydrogen bonds,solvation dynamics
更新于2025-09-09 09:28:46
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A BOSE-EINSTEIN CONDENSATE WITH PT-SYMMETRIC DOUBLE-DELTA FUNCTION LOSS AND GAIN IN A HARMONIC TRAP: A TEST OF RIGOROUS ESTIMATES
摘要： We consider the linear and nonlinear Schr?dinger equation for a Bose-Einstein condensate in a harmonic trap with PT -symmetric double-delta function loss and gain terms. We verify that the conditions for the applicability of a recent proposition by Mityagin and Siegl on singular perturbations of harmonic oscillator type self-adjoint operators are ful?lled. In both the linear and nonlinear case we calculate numerically the shifts of the unperturbed levels with quantum numbers n of up to 89 in dependence on the strength of the non-Hermiticity and compare with rigorous estimates derived by those authors. We con?rm that the predicted 1/n1/2 estimate provides a valid upper bound on the shrink rate of the numerical eigenvalues. Moreover, we ?nd that a more recent estimate of log(n)/n3/2 is in excellent agreement with the numerical results. With nonlinearity the shrink rates are found to be smaller than without nonlinearity, and the rigorous estimates, derived only for the linear case, are no longer applicable.
关键词： perturbed harmonic oscillator,PT symmetry,Bose-Einstein condensates
更新于2025-09-09 09:28:46
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CPT and Lorentz Violation in the Photon and Z-Boson Sector
摘要： Violation of CPT and Lorentz symmetry in the photon sector is described within the minimal Standard-Model Extension by a dimension-3 Chern–Simons-like operator parametrized by a four-vector parameter kAF that has been very tightly bounded by astrophysical observations. On the other hand, in the context of the SU(2) × U(1) electroweak gauge sector of the Standard-Model Extension, CPT and Lorentz violation is described similarly, by dimension-3 operators parametrized by four-vector parameters k1 and k2. In this work, we investigate in detail the effects of the resulting CPT and Lorentz violation in the photon and Z-boson sectors upon electroweak-symmetry breaking. In particular, we show that, for the photon sector, the relevant Lorentz-violating effects are described at the lowest order by the kAF term, but that there are higher-order momentum-dependent effects due to photon-Z boson mixing. As bounds on CPT and Lorentz violation in the Z sector are relatively weak, these effects could be important phenomenologically. We investigate these effects in detail in this work.
关键词： Lorentz violation,dispersion relations,electroweak symmetry breaking
更新于2025-09-09 09:28:46
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Conductance Spectroscopy of Exfoliated Thin Flakes of Nb <sub/>x</sub> Bi <sub/>2</sub> Se <sub/>3</sub>
摘要： We study unconventional superconductivity in exfoliated single crystals of a promising 3D topological superconductor candidate, Nb-doped Bi2Se3 through differential conductance spectroscopy and magneto-transport. The strong anisotropy of the critical field along the out-of-plane direction suggests that the thin exfoliated flakes are in the quasi-2D limit. Normal metal-superconductor (NS) contacts with either high or low transparencies made by depositing gold leads onto Nb-doped Bi2Se3 flakes both show significant enhancement in zero bias conductance and coherence dips at the superconducting energy gap. Such behavior is inconsistent with conventional Blonder-Tinkham-Klapwijk theory. Instead, we discuss how our results are consistent with p-wave pairing symmetry, supporting the possibility of topological superconductivity in Nb-doped Bi2Se3. Finally, we observe signatures of multiple superconducting energy gaps, which could originate from multiple Fermi surfaces reported earlier in bulk crystals.
关键词： differential conductance spectroscopy,unconventional superconductivity,topological superconductivity,p-wave pairing symmetry,Nb-doped Bi2Se3
更新于2025-09-09 09:28:46
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Fundamentals of Electroceramics (Materials, Devices, and Applications) || Binding Forces in Solids and Essential Elements of Crystallography
摘要： In this chapter, we will study how the solids are held together in a structure that can be either polycrystalline or single crystal, how solids are classified based on their governing binding forces, the relationship between structures and the properties they acquire when subjected to an external agent such as an electric or a magnetic field, and, finally, how these properties help engineers and scientists develop devices and their applications. We will also study the nature and properties of single crystals and how their unique properties help us in understanding their importance to science and technology.
关键词： Dielectric Materials,Crystal Structures,Symmetry Elements,Crystallography,Binding Forces
更新于2025-09-09 09:28:46
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Microwave edge modes on a metasurface with glide symmetry
摘要： In this work we study planar metasurfaces comprised of two layers of hexagonal arrays of circular metal patches. This two-layer geometry supports a bound surface wave that propagates along the x direction. In our study, each metasurface is in?nitely periodic in one direction (x) but only a few periods wide in the orthogonal direction (y). Through experiments and modeling we ?nd evidence of a localized edge mode whose existence is dependent on the relative alignment of the two layers. This edge mode is used to guide the propagation of electromagnetic energy around both triangular and hexagonal shapes.
关键词： metasurface,electromagnetic energy propagation,glide symmetry,microwave edge modes
更新于2025-09-09 09:28:46
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Nanometer-scale local structural study of the paraelectric cubic phase of KNbO <sub/>3</sub> by convergent-beam electron diffraction
摘要： Nanometer-scale local structures of the paraelectric cubic phase of potassium niobate (KNbO3) are examined by convergent-beam electron diffraction (CBED) using a nanometer-size electron probe. The breaking of the cubic symmetry has been directly observed in the nanometer-scale areas of the cubic phase of KNbO3. This indicates the existence of local polarization clusters in the cubic phase. Symmetry breaking index maps for the fourfold rotation symmetry are given at different temperatures with the combined use of scanning transmission electron microscopy (STEM) and CBED (STEM–CBED). ? 2017 The Japan Society of Applied Physics
关键词： local polarization clusters,CBED,convergent-beam electron diffraction,STEM,KNbO3,symmetry breaking
更新于2025-09-09 09:28:46
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A quad polarimetric SAR calibration algorithm using rotation symmetry
摘要： Polarimetric calibration, precisely deciphering the polarimetric information hidden in the polarized characteristics of a radar scene, is the core step before applying quad polarimetric synthetic aperture radar (PolSAR) data for ground parameter inversion and classification. The previously published techniques for polarimetric calibration generally use at least one known point calibration target to completely determine the polarimetric distortions (cross-talks and channel imbalances) between the various polarized channels. This paper describes a novel method that solely relies on the image itself with the property of rotation symmetry. The algorithm derives the entire cross-talk and channel imbalance parameters using an iterative operation to circularly modify the observed average covariance matrix, which is independent on the known point calibration targets in the illuminated scene. The proposed method is validated to be reliable and efficient through polarimetric calibration experiments using the airborne C-band and RadarSat-2 quad polarimetric SAR images. The experimental results indicate that the new technique achieves similar calibration precision to the Ainsworth algorithm but without using any known calibration point target.
关键词： Polarimetric calibration,cross-talk,channel imbalance,quad polarimetric SAR,rotation symmetry
更新于2025-09-09 09:28:46