- 标题
- 摘要
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- 实验方案
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All-optical radio-frequency modulation of Anderson-localized modes
摘要： All-optical modulation of light relies on exploiting intrinsic material nonlinearities [V. R. Almeida et al., Nature 431, 1081 (2004)]. However, this optical control is rather challenging due to the weak dependence of the refractive index and absorption coefficients on the concentration of free carriers in standard semiconductors [R. A. Soref and B. R. Bennett, Proc. SPIE 704, 32 (1987)]. To overcome this limitation, resonant structures with high spatial and spectral confinement are carefully designed to enhance the stored electromagnetic energy, thereby requiring lower excitation power to achieve significant nonlinear effects [K. Nozaki et al., Nat. Photonics 4, 477 (2010)]. Small mode-volume and high-quality (Q)-factor cavities also offer an efficient coherent control of the light field and the targeted optical properties. Here, we report on optical resonances reaching Q ～ 105 induced by disorder on photonic/phononic-crystal waveguides. At relatively low excitation powers (below 1 mW), these cavities exhibit nonlinear effects leading to periodic (up to ～35 MHz) oscillations of their resonant wavelength. Our system represents a test bed to study the interplay between structural complexity and material nonlinearities and their impact on localization phenomena and introduces a different functionality to the toolset of disordered photonics.
关键词： nonlinear effects,disorder-induced cavities,Anderson-localized modes,all-optical modulation,photonic/phononic-crystal waveguides
更新于2025-09-10 09:29:36
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Atomic ordering, magnetic properties, and electronic structure of Mn<sub>2</sub>CoGa Heusler alloy
摘要： The magnetic properties and atomic arrangement of Mn2CoGa Heusler alloy were investigated experimentally and by theoretical calculations. The magnetic moment derived from spontaneous magnetization at 5 K was 2.06 μB/f.u. and was close to the integer number of the expected value from theoretical calculation and the Slater–Pauling rule predicted by Galanakis et al. The Curie temperature and L21-B2 order-disorder phase transition temperature were 741 and 1047 K, respectively. Powder neutron diffraction experiment results suggested that the atomic arrangement prefers an L21b-type structure rather than that of Hg2CuTi, being consistent with our previous results of high-angle annular dark-field-scanning transmission electron microscopic observations. The magnetic moments obtained were in good agreement with the theoretical values in the model of the L21b-type structure. The density of states obtained by the first-principles calculation combined with the coherent potential approximation in Mn2CoGa with the L21b-type crystal structure maintained the half-metallic character, even though disordering by Mn and Co atoms was introduced.
关键词： powder neutron diffraction,magnetic moment,Half-metal-type ferromagnets,order-disorder phase transition,atomic ordering,Curie temperature
更新于2025-09-09 09:28:46
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Nodal points of Weyl semimetals survive the presence of moderate disorder
摘要： In this work we address the physics of individual three-dimensional Weyl nodes subject to a moderate concentration of disorder. Previous analysis indicates the presence of a quantum phase transition below which disorder becomes irrelevant and the integrity of sharp nodal points of vanishing spectral density is preserved in this system. This statement appears to be at variance with the inevitable presence of statistically rare fluctuations which cannot be considered as weak and must have strong influence on the system’s spectrum, no matter how small the average concentration. We here reconcile the two pictures by demonstrating that rare fluctuation potentials in the Weyl system generate a peculiar type of resonances which carry spectral density in any neighborhood of zero energy, but never at zero. In this way, the vanishing of the DoS for weak disorder survives the inclusion of rare events. We demonstrate this feature by considering three different models of disorder, each emphasizing specific aspects of the problem: a simplistic box potential model, a model with Gaussian distributed disorder, and one with a finite number of s-wave scatterers. Our analysis also explains why the protection of the nodal DoS may be difficult to see in simulations of finite size lattices.
关键词： Weyl semimetals,rare fluctuations,disorder,spectral density,quantum phase transition
更新于2025-09-09 09:28:46
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Alloy-assisted Auger recombination in InGaN
摘要： It has been numerically investigated the effect of alloying on the Auger recombination rate in wurtzite type n-InGaN. In order to explicitly take into account the effect of alloy disorder, the calculations have been performed with a 256-atom supercell that includes In and Ga atoms randomly distributed over the supercell sites to obtain a given composition. A full band structure (no band scissors-shifting) and high-dense inhomogeneous k-point grid were used to improve the accuracy of the calculations. We show that the large number of allowed interband Auger transitions originated by the breaking of the translational periodicity plays a crucial role in the wide band gap InGaN alloys. The alloy-assisted Auger coefficients for these alloys are in the 1.0 × 10?32–4.7 × 10?31 cm6/s range
关键词： InGaN alloys,Atomic disorder,Supercell,Auger recombination
更新于2025-09-09 09:28:46
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Disorder effect on photoconductivity properties in metallic Pb<sub>1-x</sub>Eu<sub>x</sub>Te epitaxial layers
摘要： In this work, we present photoconductivity measurements performed on metallic p-type Pb1-xEuxTe epitaxial films for x~ 0.02 and x~0.03 in the temperature range of 77K – 300K. The results show that sample with x~ 0.02 presented negative photoconductivity effect in the whole range of temperatures measured, while sample with x~0.03 presented a transition from positive to negative photoconductivity. Hall measurements were also performed to investigate the effects observed in both samples, but could not give any conclusive explanation. On the other hand, we showed that disorder changes considerably the generation/recombination ratios as temperature is varied giving rise to the anomalous effects observed.
关键词： disorder,PbEuTe,Photoconductivity
更新于2025-09-09 09:28:46
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Radiative lifetime of localized excitons in transition-metal dichalcogenides
摘要： Disorder derived from defects or local strain in monolayer transition-metal dichalcogenides (TMDs) can lead to a dramatic change in the physical behavior of the interband excitations, producing inhomogeneous spectral broadening and localization leading to radiative lifetime increase. In this study, we have modeled the surface disorder of a monolayer TMD sample through a randomized potential in the layer plane. We show that this model, applied to a monolayer of WSe2, allows us to simulate the spectra of localized exciton states as well as their radiative lifetime. In this context, we give an in depth study of the in?uence of the disorder potential parameters on the optical properties of these defects through energies, density of states, oscillator strengths, photoluminescence (PL) spectroscopy, and radiative lifetime at low temperature (4 K). We demonstrate that localized excitons have a longer emission time than free excitons, in the range of tens of picoseconds or more, the radiative decay time depending strongly on the disorder parameter and dielectric environment. Finally, in order to prove the validity of our model, we compare it to available experimental results of the literature.
关键词： disorder potential,localized excitons,radiative lifetime,transition-metal dichalcogenides,photoluminescence spectroscopy
更新于2025-09-09 09:28:46
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Optical study of stress hormone-induced nanoscale structural alteration in brain using partial wave spectroscopic (PWS) microscopy
摘要： Chronic stress affects nano to microscale structures of the brain cells/tissues due to suppression of neural growths and reconnections, hence the neuronal activities. This results in depression, memory loss and even death of the brain cells. Our recently developed novel optical technique, partial wave spectroscopic (PWS) microscopy has nanoscale sensitivity, and hence, can detect nanoscale changes in brain tissues due to stress. In this study, we applied this technique to quantify the stress related structural changes in the corticosterone-treated mouse model of stress. Our results show that brains from corticosterone-treated mice showed higher nanoscale structural disorder in the hippocampal region as compared to the brain from normal (vehicle) mice. The increase in structural alteration correlates with the duration of the stress. We further quantified the relative changes and the spatial localization of these changes in this mouse model and found out that the maximum changes occurred nearly symmetrically in both regions of the hippocampus. The mRNA for stress-related genes, BDNF and TrkB were also significantly reduced in the hippocampus of corticosterone-treated mice compared to that in control mice. These results indicate that chronic corticosterone treatment induces nanoscale structural alterations in mouse brain that corresponds to changes in stress-related gene expression.
关键词： brain tissues,Stress,disorder strength,PWS,hippocampus,corticosterone
更新于2025-09-09 09:28:46
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Unraveling the Role of Multiphonon Excitations and Disorder Concerning the Meyer-Neldel Type Compensation Effect in Organic Semiconductors
摘要： The Meyer-Neldel (MN) compensation rule, implying an exponential increase in the prefactor with increasing activation energy in a thermally activated process, is naturally emerging in two-site transition rates as a result of multiphonon excitation processes. However, it has been recently demonstrated [Phys. Rev. B. 90, 245201 (2014)] that the experimentally observed compensation behavior for the temperature-activated charge transport in thin-film organic field-effect transistors (OFETs) is not a genuine phenomenon, but rather it is an apparent extrapolated effect that arises as a consequence of the partial filling of the Gaussian DOS distribution. To resolve the contradiction, we investigate the impact of different jump-rate models on macroscopic hopping-charge transport in a random organic system using an effective medium analytic approach. The principal result of this study is that the averaging over the individual jump rates in a conventional Gaussian disordered system erodes the genuine thermodynamically determined MN compensation effect, and therefore, the macroscopic transport no longer reflects the microscopic rates. The apparent compensation behavior observed for OFET mobilities upon varying the carrier concentrations can be reproduced regardless of the single-phonon or multiphonon character of activated transitions. Another remarkable finding is that the disorder formalism does predict a genuine MN compensation effect using multiphonon rates if a disordered semiconductor contains a significant concentration of deep traps, so that the cumulative DOS features a double-peak Gaussian. Thus, this study bridges the gap between Gaussian disorder and multi-excitation entropy (MEE) models concerning the MN effect, and has important implications for the interpretation of the isokinetic MN temperature in disordered organic semiconductors.
关键词： disorder,organic semiconductors,multiphonon excitations,charge transport,Meyer-Neldel rule
更新于2025-09-09 09:28:46
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Optogenetics in preclinical neuroscience and psychiatry research: recent insights and potential applications
摘要： There have been significant advances in the treatment of psychiatric disease in the last half century, but it is still unclear which neural circuits are ultimately responsible for specific disease states. Fortunately, technical limitations that have constrained this research have recently been mitigated by advances in research tools that facilitate circuit-based analyses. The most prominent of these tools is optogenetics, which refers to the use of genetically encoded, light-sensitive proteins that can be used to manipulate discrete neural circuits with temporal precision. Optogenetics has recently been used to examine the neural underpinnings of both psychiatric disease and symptom relief, and this research has rapidly identified novel therapeutic targets for what could be a new generation of rational drug development. As these and related methodologies for controlling neurons ultimately make their way into the clinic, circuit-based strategies for alleviating psychiatric symptoms could become a remarkably refined approach to disease treatment.
关键词： obsessive-compulsive disorder,optogenetics,addiction,anxiety,depression
更新于2025-09-09 09:28:46
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Progressive Visusminderung bei Zapfendystrophie. Spurensuche im Makula-OCT und Multifokal-ERG; Progressive loss of vision in cone dystrophy. Search for evidence with macular OCT and multifocal ERG;
摘要： A 53-year-old patient consulted our practice clinic complaining of progressive visual loss, increased glare sensitivity and color sense disorder. Extensive diagnostic investigation, including multifocal ERG (mfERG) and macular thickness map with the help of optical coherence tomography (OCT), supported the suspected diagnosis of a cone dystrophy. There are, however, no established therapeutic options. A diagnostic confirmation by means of molecular genetics was not successful.
关键词： Molecular genetics,Central scotoma,Glare sensitivity,Macular thickness map,Color sense disorder
更新于2025-09-04 15:30:14