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Torsionally induced exciton localization and decoherence in <i>π</i> -conjugated polymers
摘要： We develop a model of excitons coupled to the rotational motion of monomers to study the torsionally induced relaxation and decoherence of excitons in π-conjugated polymers. The model assumes that the monomer units are described by elastically uncoupled harmonic oscillators and that there is a linear exciton-roton coupling. Although the rotational degrees of freedom are much slower than the exciton, so that the adiabatic approximation is generally expected to be valid, we also investigate possible quantized roton corrections via coupled time evolving block decimation-Ehrenfest equations of motion. For the relaxation of the lowest-excited exciton, we find that (1) for a polymer chain with a ground state spiral torsional conformation, the equilibrium angular displacement of each monomer is proportional to the difference of the exciton bond-orders on the neighboring bridging bonds. Consequently, this displacement vanishes in the long chain limit and a classical (Landau) exciton-polaron is not formed. (2) For a polymer chain with a ground state staggered torsional conformation, the equilibrium angular displacement of each monomer is proportional to the sum of the exciton bond-orders on the neighboring bridging bonds. Consequently, there is significant angular displacement and local planarization causing exciton density localization. A classical (Landau) exciton-polaron is formed where the staggered angular displacement is proportional to the exciton density. (3) Generally, in the adiabatic limit, the decay of off-diagonal long-range order (i.e., exciton decoherence) mirrors the localization of the exciton density. However, quantum corrections to the rotational motion alter this adiabatic prediction because of correlated exciton-roton dynamics within the first rotational half-period. In particular, exciton-polaron quasiparticle formation causes more rapid and oscillatory exciton decoherence and slower exciton density localization.
关键词： π-conjugated polymers,exciton,decoherence,torsional relaxation,Landau exciton-polaron
更新于2025-09-04 15:30:14
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Improving LiDAR classification accuracy by contextual label smoothing in post-processing
摘要： We propose a contextual label-smoothing method to improve the LiDAR classification accuracy in a post-processing step. Under the framework of global graph-structured regularization, we enhance the effectiveness of label smoothing from two aspects. First, each point can collect sufficient label-relevant neighborhood information to verify its label based on an optimal graph. Second, the input label probability set is improved by probabilistic label relaxation to be more consistent with the spatial context. With this optimal graph and reliable label probability set, the final labels are computed by graph-structured regularization. We demonstrate the contextual label-smoothing approach on two separate urban airborne LiDAR datasets with complex urban scenes. Significant improvements in the classification accuracies are achieved without losing small objects (such as fa?ades and cars). The overall accuracy is increased by 7.01% on the Vienna dataset and 6.88% on the Vaihingen dataset. Moreover, most large, wrongly labeled regions are corrected by long-range interactions that are derived from the optimal graph, and misclassified regions that lack neighborhood communications in terms of correct labels are also corrected with the probabilistic label relaxation.
关键词： Neighborhood dependency,Optimal neighborhood,Point cloud,Probabilistic label relaxation
更新于2025-09-04 15:30:14
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Calculation of the frequency shifts and damping constant for the Raman modes (A$_{1g}$, B$_{1})$ near the tetragonal-cubic transition in SrTiO$_{3}$
摘要： Raman shifts of the soft mode A 1g and the B 1 mode are calculated at various pressures at room temperature for the cubic-tetragonal transition (P C = 9.5 GPa) in SrTiO 3 . This calculation is performed using the observed volume data through the mode Gr(cid:127)uneisen parameters of A 1g and B 1 , which vary with pressure, by (cid:12)tting to the experimental wavenumbers in this crystalline system. Calculated Raman shifts are then used as order parameters to predict the pressure dependence of the damping constant and the inverse relaxation time for the cubic-tetragonal transition in SrTiO 3 . Our predictions from the pseudospin-phonon coupling and the energy (cid:13)uctuation models can be compared with the experimental measurements when available in the literature.
关键词： SrTiO 3,inverse relaxation time,Raman wavenumber,mode Gr(cid:127)uneisen parameter,damping constant
更新于2025-09-04 15:30:14
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Enhanced Luminescence from InGaN/GaN Nano-disk in a wire Array Caused by Surface Potential Modulation during Wet Treatment
摘要： Here we have demonstrated the profound impact of surface potential on the luminescence of an array of InGaN/GaN nano-disk in a wire heterostructure. The change in surface potential is brought about by a combination of dry and successive wet-processing treatments. The photoluminescence (PL) properties are determined as a function of size and varying surface potential. The change in hole bound state energy due to parabolic potential well near the side-wall is found to be the dominating factor. The PL peak position, full width at half-maximum (FWHM), strain relaxation and integrated PL intensity are studied as a function of incident power and temperature. The devices demonstrate higher integrated PL intensity and slope efficiency.
关键词： exciton binding energy,photoluminescence,QCSE,nano-disk,surface potential,strain relaxation,InGaN/GaN,quantum confinement
更新于2025-09-04 15:30:14
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Collective Jahn-Teller Interactions through Light-Matter Coupling in a Cavity
摘要： The ultrafast nonradiative relaxation of a molecular ensemble coupled to a cavity mode is considered theoretically and by real-time quantum dynamics. For equal coupling strength of single molecules to the cavity mode, the nonradiative relaxation rate from the upper to the lower polariton states is found to strongly depend on the number of coupled molecules. The coupling of both bright and dark polaritonic states among each other constitutes a special case of (pseudo-)Jahn-Teller interactions involving collective displacements the internal coordinates of the molecules in the ensemble, and the strength of the first order vibronic coupling depends exclusively on the gradient of the energy gaps between molecular electronic states. For N > 2 molecules, the N ? 1 dark light-matter states between the two optically active polaritons feature true collective conical intersection crossings, whose location depends on the internal atomic coordinates of each molecule in the ensemble, and which contribute to the ultrafast nonradiative decay from the upper polariton.
关键词： conical intersection crossings,nonradiative relaxation,cavity mode,Jahn-Teller interactions,polaritonic states,molecular ensemble
更新于2025-09-04 15:30:14
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Spin–orbit coupling in silicon for electrons bound to donors
摘要： Spin–orbit coupling (SOC) is fundamental to a wide range of phenomena in condensed matter, spanning from a renormalisation of the free-electron g-factor, to the formation of topological insulators, and Majorana Fermions. SOC has also profound implications in spin-based quantum information, where it is known to limit spin lifetimes (T1) in the inversion asymmetric semiconductors such as GaAs. However, for electrons in silicon—and in particular those bound to phosphorus donor qubits—SOC is usually regarded weak, allowing for spin lifetimes of minutes in the bulk. Surprisingly, however, in a nanoelectronic device donor spin lifetimes have only reached values of seconds. Here, we reconcile this difference by demonstrating that electric ?eld induced SOC can dominate spin relaxation of donor-bound electrons. Eliminating this lifetime-limiting effect by careful alignment of an external vector magnetic ?eld in an atomically engineered device, allows us to reach the bulk-limit of spin-relaxation times. Given the unexpected strength of SOC in the technologically relevant silicon platform, we anticipate that our results will stimulate future theoretical and experimental investigation of phenomena that rely on strong magnetoelectric coupling of atomically con?ned spins.
关键词： silicon,spin relaxation,Spin–orbit coupling,donor-bound electrons,quantum information
更新于2025-09-04 15:30:14
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Structure, dielectric properties of low-temperature-sintering BaTiO <sub/>3</sub> -based glass–ceramics for energy storage
摘要： The 0.85BaTiO3–0.15Bi(Mg2/3Nb1/3)O3 (BTBMN) ceramics with low-melting-temperature B2O3–Na2B4O7–Na2SiO3 (BNN) glass addition were prepared by the solid state method. The composition of the glass–ceramics was BTBMN–x wt.% BNN (x = 0, 1, 3, 5, 7, 9, 12, 15; abbreviated as BG). The sintering characteristics, phase structure, microstructure, dielectric properties and energy storage properties were systematically investigated. The sintering temperature of BTBMN ceramics was greatly reduced by the addition of BNN glass. The second-phase BaTi(BO3)2 was observed in the BG system until the glass content reached 15 wt.%. The addition of BNN glass significantly reduces the grain size of BTBMN ceramics. With the increase of BNN glass content, dielectric constant of BG glass–ceramics at 1 kHz gradually decreased, the maximum dielectric constant (εm) of BG glass–ceramics gradually decreased, while the temperature corresponding to the maximum dielectric constant (Tm) increased, the ferroelectric relaxation behavior decreased and the temperature stability of the dielectric constant gradually improved. As the BNN glass content increased, the breakdown electric field strength (BDS) of BG glass–ceramics increased first and then decreased, and the polarization values reduced gradually, while the trend of energy storage performance is similar to BDS. When the BNN glass content was 3 wt.%, the energy storage properties of the BG glass–ceramics were optimal, and a recoverable energy storage density (Wrec) of 1.26 J/cm3 and an energy storage efficiency (η) of 80.9% were obtained at the electric field strength of 220 kV/cm. The results showed that BG glass–ceramics were promising for energy storage capacitors.
关键词： Lead-free,glass–ceramics,relaxation,energy storage properties,BaTiO3
更新于2025-09-04 15:30:14
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Local Strain and Crystalline Defects in GaN/AlGaN/GaN(0001) Heterostructures Induced by Compositionally Graded AlGaN Buried Layers
摘要： Plastic strain relaxation in epitaxial layers is one of the crucial factors that limit the performance of III-nitride-based heterostructures. In this work, we report on strain relaxation and crystalline defects in heterostructures consisting of compositionally graded AlGaN epitaxial layers tensile-strained between a GaN-buffer and a GaN-cap. We demonstrate the effects of Al concentration and the shape of the concentration-depth profile in the buried graded layers on the accumulated elastic strain energy and how this influences the critical thickness for crack generation or fracture. It is shown that this fracture leads to the formation of partially relaxed regions with their degree of strain relaxation directly related to the density of cracks. Nevertheless, even though the in-plane coherency between the AlGaN layer and the GaN-buffer is broken, the in-plane coherency within the AlGaN layer is preserved for all regions. Furthermore, the tensile strain released in the buried graded AlGaN layers is consistent with compressive strain induced in the GaN-cap layers. Finally, the localized stress and the densities of threading dislocations are correlated with the features of the resulting fractured heterostructures. These results are important towards the control of complex plastic strain relaxation and further facilitate the growth of high quality compositionally graded AlGaN-based devices.
关键词： X-ray diffraction,cracks,graded layers,epitaxy,strain relaxation,AlGaN
更新于2025-09-04 15:30:14