Nonlinear Redshift Research Articles

Near- and far-field study of polarization-dependent surface plasmon resonance in bowtie nano-aperture arrays.

Bowtie nano-apertures can confine light into deep subwavelength volumes with extreme field enhancement, making them a useful tool for various applications such as optical trapping, deep subwavelength imaging, nanolithography, and sensors. However, the correlation between the near- and far-field properties of bowtie nano-aperture arrays has yet to be fully explored. In this study, we experimentally investigated the polarization-dependent surface plasmon resonance in bowtie nano-aperture arrays using both optical transmission spectroscopy and photoemission electron microscopy. The experimental results reveal a nonlinear redshift in the transmission spectra as the gap size of the bowtie nanoaperture decreases for vertically polarized light, while the transmission spectra remain unchanged with different gap sizes for horizontally polarized light. To elucidate the underlying mechanisms, we present simulated charge and current distributions, revealing how the electrons respond to light and generate the plasmonic fields. These near-field distributions were verified by photoemission electron microscopy. This study provides a comprehensive understanding of the plasmonic properties of bowtie nano-aperture, enabling their further applications, one of which is the optical switching of the resonance wavelength in the widely used visible spectral region without changing the geometry of the nanostructure.

Probing the thermally driven response of Raman-active phonon modes in sapphire single crystals by in situ Raman spectroscopy

Given the practical application of sapphire as a promising transparent crystal in extreme environments, understanding the fundamental physical response of its optical properties to temperature is urgently needed. Herein, the vibrational characteristics of Raman-active modes of the strain-free sapphire and the strained sapphire substrate under the AlN epilayer were systematically investigated by Raman scattering measurements in the temperature range of 95–870 K. The observed nonlinear temperature-dependent frequency redshift for all phonon modes over the entire temperature range can be fitted with some empirical formulas. Interestingly, the frequency of these phonon modes varies linearly with temperature at high temperatures and can be explained by first-order temperature coefficients. The linear temperature coefficients of A1g,1 modes for strain-free sapphire and strained sapphire determined at high temperatures are −0.02224 cm−1/K and −0.02189 cm−1/K, respectively. The strong temperature dependence in sapphire is expected to portray the local temperature distribution of sapphire-based devices by in situ Raman spectroscopy as a non-contact thermal probe. Furthermore, the frequency downshift and linewidth broadening observed in strain-free sapphire can be well quantified by a theoretical model involving thermal expansion and anharmonic decay. The epilayer-substrate interaction, however, needs to be additionally considered in strained sapphire. This theoretical analysis process can also be radically extended to other emerging ceramic and semiconductor materials. Our quantitative analysis may pave the way for a deeper understanding of the behavior of optical phonons in sapphire under extra perturbation effects.

Phonon anharmonicity in exfoliated black arsenic flakes

Black arsenic (b-As) with extreme in-plane anisotropy, incredible ambient stability, and excellent transport performance has unlimited potential for device applications. Uncovering phonon–phonon (ph–ph) interactions is a critical step in understanding its transport, especially thermal transport properties. Here, we report on the phonon anharmonicity in an exfoliated b-As flake using temperature-dependent polarized Raman spectroscopy from 80 to 300 K. Polarization of Ag2 mode helps identifying the crystalline orientation of the flake. A nonlinear redshift of peak frequencies of Ag1, B2g, and Ag2 modes is observed along the given crystalline orientation. Contributions from intrinsic ph–ph interactions are extracted: cubic-phonon decay dominates the ph–ph scattering processes at low temperature, while cubic- and quartic-phonon decays together do at high temperature. It is further confirmed by the nonlinear full-width-at-half-maxima broadening. Our findings disclose the phonon anharmonicity in b-As and give insight for better understanding and utilizing its thermodynamic properties.

Investigation of the Electron–Phonon Coupling in Dirac Semimetal PdTe2 via Temperature‐Dependent Raman Spectroscopy

Layered Palladium ditelluride (PdTe2) is an interesting noble‐transition‐metal dichalcogenide with high electrical and thermal conductivity, exhibiting superconductivity and a type‐II Dirac semimetallic phase due to the increased electron–phonon (e–ph) coupling. Herein, the e–ph coupling constant λ of E g (in‐plane) and A 1g (out‐of‐plane) modes in the exfoliated PdTe2 nanoflakes via temperature‐dependent Raman spectroscopy within the temperature range from 80 to 580 K is determined. Both E g mode with a Gaussian line shape and A 1g mode with a Breit–Wigner–Fano line shape show nonlinear frequency redshift and linewidth broadening with temperature. The extracted e–ph coupling constants are = 1.54 and = 0.55, respectively. The Raman results confirm that PdTe2 is a phonon‐mediated Bardeen–Cooper–Schrieffer superconductor.

Loaded Slot Cavity Induced Sensing Enhancement and Transparency Based on Plasmonic Structure

Biosensors have proved immensely useful in numerous vital areas for detection and testing. Here, a novel plasmonic nanosensor, based on loaded slot cavity, is proposed and studied. We conduct a detailed analysis of the influence of the load’s parameters on the transmission characteristics based on the finite element method and surface charge and current model. Simulation results reveal that the existence of the load can cause the resonant wavelength to have a linear or nonlinear red shift, and yield an enhanced plasmonic nanosensor with sensitivity about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}={2900}$ </tex-math></inline-formula> nm/RIU and a detection limit about 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times \,\,10^{\text {-3}}$ </tex-math></inline-formula> . In addition, the proposed structure is well used in actual biosensing for blood plasma concentration, glucose concentration, ethanol temperature and diseased cell detection with high sensitivity. Finally, an extended structure with detuned loaded slot cavities is proposed to realize PIT/multi-PIT and slow light effect. The special features of our proposed structure are applicable in the realization of various integrated components for the development of high-performance plasmonic biosensor.

Temperature‐ and pressure‐dependent phonon dynamics properties of gallium selenide telluride

AbstractUnderstanding the thermodynamic properties of materials is a fundamental issue in physics, and its knowledge is crucial for targeting a specific material for possible applications. In this work, we report a temperature‐ and pressure‐dependent Raman study of bulk GaSe0.5Te0.5 alloy, besides their relevant thermodynamic parameters. Our results show a nonlinear redshift for the and vibrational modes as the temperature increases in the temperature range from 10 to 748 K. Such behavior is well described by considering both thermal expansion and phonon–phonon coupling contributions. By combining density functional theory (DFT) calculations and Raman spectroscopy experiments, the anharmonic constants relative to the three‐ and four‐phonon decay processes, mode‐Grüneisen parameters, Debye temperature, thermal expansion coefficient, and bulk modulus were estimated for GaSe0.5Te0.5 alloy. Furthermore, the high‐pressure measurements and DFT calculations, performed in the pressure range from 0 to 26.4 GPa, show a quadratic trend for the and modes as a function of pressure, with the modes being more compressible than one, that is, . No structural phase transition is observed until the maximum pressure reached in the experiment. This study took a step forward in the understanding of mechanical and thermal properties related to GaSe0.5Te0.5 alloy, whose determined parameters are important for designing new applications.

Precision analysis of the redshift-space galaxy bispectrum

We study the information content of the angle-averaged (monopole) redshift space galaxy bispectrum. The main novelty of our approach is the use of a systematic tree-level perturbation theory model that includes galaxy bias, IR resummation, and also accounts for nonlinear redshift space distortions, binning, and projection effects. We analyze data from the PT challenge simulations, whose cumulative volume of 566 $h^{-3}$Gpc$^3$ allows for a precise comparison to theoretical predictions. Fitting the power spectrum and bispectrum of our simulated data, and varying all necessary cosmological and nuisance parameters in a consistent Markov chain Monte Carlo analysis, we find that our tree-level bispectrum model is valid up to $k_{\max}=0.08~h{\rm Mpc}^{-1}$ (at $z=0.61$). We also find that inclusion of the bispectrum monopole improves constraints on cosmological parameters by $(5-15)\%$ relative to the power spectrum. The improvement is more significant for the quadratic bias parameters of our simulated galaxies, which we also show to deviate from biases of the host dark matter halos at the $\sim 3\sigma$ level. Finally, we adjust the covariance and scale cuts to match the volume of the BOSS survey, and estimate that within the minimal $\Lambda$CDM model the bispectrum data can tighten the constraint on the mass fluctuation amplitude $\sigma_8$ by roughly $10\%$.

Optical spectra of the quantum defects in metal halide perovskites

Defects in metal halide perovskites (MHPs) are of fundamental importance to understand optical properties of materials. Here, optical transitions of negative, positive, and neutral defects in MHPs are studied based on the quantum defect model. We find that the intensities of emission peaks are obviously enhanced along with a nonlinear redshift as the depth of defect levels increases in the bandgap. Moreover, the full width at half-maximum of emission spectra can be broadened from tens to hundreds of meV with the increasing temperature. This can be attributed to the strong defect-longitudinal optical phonon coupling, resulting in the enhanced lattice relaxation effect, which could be used as a judging criterion between defects and exciton emission. These results not only provide deep insight for the properties of defect's spectra but also shed light on the influence of defects on the potential applications of MHP-based optoelectronic devices.

Wavelength and decay time tuning of intraband transitions in low spatial frequency laser-induced periodic surface structures

We present the study of the alteration of wavelength and decay time of intraband transitions in the laser-induced periodic surface structures (LIPSS) of silver formed by varying the incident laser peak fluence. The studies are performed using a femtosecond laser (λ0 = 800 nm) based ultrafast transient absorption spectroscopy (UFTS)setup. Using the same laser, an array (~2 mm size) of laser-induced periodic surface structures were obtained in a single-step fabrication process in the open air without translating the sample. Each unit cell of the array comprises low spatial frequency LIPSS (LSFL) near the center with nanoparticles/clusters around the edges. As obtained from 2D Fast Fourier Transform, the overall periodicity(Λ) of LSFL is within 0.714λ0–0.723λ0 range. The nanoparticles/clusters show a random size distribution that varies from 50 nm to 300 nm. In UFTS measurement, the LIPSS was excited by a 3.3 eV laser. The SPP/SPR dip in the data is an indication of intraband transition or hot electron generation. The effect of change in structuring due to varying laser fluence on these intraband transitions is also analyzed. It is observed that there is a non-linear redshift (~16 nm) in the SPR peak wavelength with a significant enhancement in the relaxation times of the hot electrons due to localized annealing of shallow defects. Therefore, a large tunability in wavelength of SPP/SPR and lifetime of hot electrons was achieved by varying the laser fluence. The study highlights the suitability of LIPSS in applications requiring efficient energy transfer, enhanced photocatalytic action, and tunable sensors.

Temperature and electric field effects on the dynamic modes in a spin current auto-oscillator

We systematically study spectral characteristics of emission microwave signal by a spin current nano-oscillator (SCNO) based on $\mathrm{Ta}{\mathrm{O}}_{x}/\mathrm{Py}(3)/\mathrm{Pt}(2)$ trilayers as a function of current, in-plane magnetic field angle, electrostatic gating, and temperature. The current dependence of spectral characteristics shows that such SCNO exhibits a single coherent oscillation mode at low currents, and then transfers into a multimode coexistence regime with several oscillation peaks, related to spatially separated oscillation regions, at high currents. The linewidth of these modes shows an exponential temperature dependence, indicating thermally activated mode transitions or mode hopping behavior among these spatially separated oscillation regions due to the mode coupling caused by strong thermal-magnon-mediated scattering rate at high temperatures. Additionally, electrostatic gating on oscillation frequency shows a temperature-independent behavior, but gets enhanced in the strongly nonlinear oscillation regime. The enhanced phenomenon is caused by a combination of nonlinear frequency redshift and driving current shift due to electric-field modulation of current-induced spin-orbit torques. The demonstrated electric-field and current control of three-terminal SCNO provides an efficient approach to developing electrically tunable microwave generators in radio frequency integrated circuits and spin-wave-based logic gates in magnonic devices.

Hybrid Pℓ(k): general, unified, non-linear matter power spectrum in redshift space

Constraints on gravity and cosmology will greatly benefit from performing joint clustering and weak lensing analyses on large-scale structure data sets. Utilising non-linear information coming from small physical scales can greatly enhance these constraints. At the heart of these analyses is the matter power spectrum. Here we employ a simple method, dubbed “Hybrid Pℓ(k)”, based on the Gaussian Streaming Model (GSM), to calculate the quasi non-linear redshift space matter power spectrum multipoles. This employs a fully non-linear and theoretically general prescription for the matter power spectrum. We test this approach against comoving Lagrangian acceleration simulation measurements performed in GR, DGP and f(R) gravity and find that our method performs comparably or better to the dark matter TNS redshift space power spectrum model {for dark matter. When comparing the redshift space multipoles for halos, we find that the Gaussian approximation of the GSM with a linear bias and a free stochastic term, N, is competitive to the TNS model.} Our approach offers many avenues for improvement in accuracy as well as further unification under the halo model.

Nonlinear contributions to angular power spectra

Future galaxy clustering surveys will probe small scales where non-linearities become important. Since the number of modes accessible on intermediate to small scales is very high, having a precise model at these scales is important especially in the context of discriminating alternative cosmological models from the standard one. In the mildly non-linear regime, such models typically differ from each other, and galaxy clustering data will become very precise on these scales in the near future. As the observable quantity is the angular power spectrum in redshift space, it is important to study the effects of non-linear density and redshift space distortion (RSD) in the angular power spectrum. We compute non-linear contributions to the angular power spectrum using a flat-sky approximation that we introduce in this work, and compare the results of different perturbative approaches with $N$-body simulations. We find that the TNS perturbative approach is significantly closer to the $N$-body result than Eulerian or Lagrangian 1-loop approximations, effective field theory of large scale structure or a halofit-inspired model. However, none of these prescriptions is accurate enough to model the angular power spectrum well into the non-linear regime. In addition, for narrow redshift bins, $\Delta z \lesssim 0.01$, the angular power spectrum acquires non-linear contributions on all scales, right down to $\ell=2$, and is hence not a reliable tool at this time. To overcome this problem, we need to model non-linear RSD terms, for example as TNS does, but for a matter power spectrum that remains reasonably accurate well into the deeply non-linear regime, such as halofit.

Optoelectronic characterization of Zn1-xCdxO thin films as an alternative to photonic crystals in organic solar cells

Zn1−xCdxO thin films spanning the whole composition range have been explored as an active region in photonic devices. The precise control of the Cd concentration, as well as its crystalline phase, allowed to characterize their optoelectronic properties. However, its application as a transparent conducting oxide material in photonics has yet to be unveiled. Here, we fabricated Zn1−xCdxO thin films via the spray pyrolysis method and confirmed their composition via Energy-dispersive X-ray spectroscopy measurements. We obtained their dielectric function through spectroscopy ellipsometry over the 300-3200 nm wavelength range and validated our model performing transmittance measurements. We observed a nonlinear red-shift of the optical bandgap while increasing Cd concentration, from 3.2 eV for ZnO to 2.9 eV for Zn0.10Cd0.90O. We found that the samples with Cd concentration > 50% have sheet resistance as low as 19.8 Ω/Square. The use of alloyed metal oxides on organic solar cells as photonic crystal structures (PhC) was also evaluated by performing finite-difference time-domain simulations. We saw an enhancement in the light absorption leading to a 39.75% increase of the short-circuit current for Zn0.25Cd0.75O PhC when compared to organic solar cells with no PhC structure.

2MTF – VI. Measuring the velocity power spectrum

We present measurements of the velocity power spectrum and constraints on the growth rate of structure $f\sigma_{8}$, at redshift zero, using the peculiar motions of 2,062 galaxies in the completed 2MASS Tully-Fisher survey (2MTF). To accomplish this we introduce a model for fitting the velocity power spectrum including the effects of non-linear Redshift Space Distortions (RSD), allowing us to recover unbiased fits down to scales $k=0.2\,h\,{\rm Mpc}^{-1}$ without the need to smooth or grid the data. Our fitting methods are validated using a set of simulated 2MTF surveys. Using these simulations we also identify that the Gaussian distributed estimator for peculiar velocities of \cite{Watkins2015} is suitable for measuring the velocity power spectrum, but sub-optimal for the 2MTF data compared to using magnitude fluctuations $\delta m$, and that, whilst our fits are robust to a change in fiducial cosmology, future peculiar velocity surveys with more constraining power may have to marginalise over this. We obtain \textit{scale-dependent} constraints on the growth rate of structure in two bins, finding $f\sigma_{8} = [0.55^{+0.16}_{-0.13},0.40^{+0.16}_{-0.17}]$ in the ranges $k = [0.007-0.055, 0.55-0.150]\,h\,{\rm Mpc}^{-1}$. We also find consistent results using four bins. Assuming scale-\textit{independence} we find a value $f\sigma_{8} = 0.51^{+0.09}_{-0.08}$, a $\sim16\%$ measurement of the growth rate. Performing a consistency check of General Relativity (GR) and combining our results with CMB data only we find $\gamma = 0.45^{+0.10}_{-0.11}$, a remarkable constraint considering the small number of galaxies. All of our results are completely independent of the effects of galaxy bias, and fully consistent with the predictions of GR (scale-independent $f\sigma_{8}$ and $\gamma\approx0.55$).

Imprint of non-linear effects on HI intensity mapping on large scales

Intensity mapping of the HI brightness temperature provides a unique way of tracing large-scale structures of the Universe up to the largest possible scales. This is achieved by using a low angular resolution radio telescopes to detect emission line from cosmic neutral Hydrogen in the post-reionization Universe. We use general relativistic perturbation theory techniques to derive for the first time the full expression for the HI brightness temperature up to third order in perturbation theory without making any plane-parallel approximation. We use this result and the renormalization prescription for biased tracers to study the impact of nonlinear effects on the power spectrum of HI brightness temperature both in real and redshift space. We show how mode coupling at nonlinear order due to nonlinear bias parameters and redshift space distortion terms modulate the power spectrum on large scales. The large scale modulation may be understood to be due to the effective bias parameter and effective shot noise.

Analytic halo approach to the bispectrum of galaxies in redshift space

We present an analytic formula for the galaxy bispectrum in redshift space on the basis of the halo approach description with the halo occupation distribution of central galaxies and satellite galaxies. This work is an extension of a previous work on the galaxy power spectrum, which illuminated the significant contribution of satellite galaxies to the higher multipole spectrum through the non-linear redshift space distortions of their random motions. Behaviors of the multipoles of the bispectrum are compared with results of numerical simulations assuming a halo occupation distribution of the LOWZ sample of the SDSS-III BOSS survey. Also presented are analytic approximate formulas for the multipoles of the bispectrum, which is useful to understanding their characteristic properties. We demonstrate that the Fingers of God effect is quite important for the higher multipoles of the bispectrum in redshift space, depending on the halo occupation distribution parameters.

Quantifying Environmental and Line-of-sight Effects in Models of Strong Gravitational Lens Systems

Abstract Matter near a gravitational lens galaxy or projected along the line of sight (LOS) can affect strong lensing observables by more than contemporary measurement errors. We simulate lens fields with realistic three-dimensional mass configurations (self-consistently including voids), and then fit mock lensing observables with increasingly complex lens models to quantify biases and uncertainties associated with different ways of treating the lens environment (ENV) and LOS. We identify the combination of mass, projected offset, and redshift that determines the importance of a perturbing galaxy for lensing. Foreground structures have a stronger effect on the lens potential than background structures, due to nonlinear effects in the foreground and downweighting in the background. There is dramatic variation in the net strength of ENV/LOS effects across different lens fields; modeling fields individually yields stronger priors for H 0 than ray tracing through N-body simulations. Models that ignore mass outside the lens yield poor fits and biased results. Adding external shear can account for tidal stretching from galaxies at redshifts , but it requires corrections for external convergence and cannot reproduce nonlinear effects from foreground galaxies. Using the tidal approximation is reasonable for most perturbers as long as nonlinear redshift effects are included. Even then, the scatter in H 0 is limited by the lens profile degeneracy. Asymmetric image configurations produced by highly elliptical lens galaxies are less sensitive to the lens profile degeneracy, so they offer appealing targets for precision lensing analyses in future surveys like LSST and Euclid.

SOMBI: Bayesian identification of parameter relations in unstructured cosmological data

This work describes the implementation and application of a correlation determination method based on Self Organizing Maps and Bayesian Inference (SOMBI). SOMBI aims to automatically identify relations between different observed parameters in unstructured cosmological or astrophysical surveys by automatically identifying data clusters in high-dimensional datasets via the Self Organizing Map neural network algorithm. Parameter relations are then revealed by means of a Bayesian inference within respective identified data clusters. Specifically such relations are assumed to be parametrized as a polynomial of unknown order. The Bayesian approach results in a posterior probability distribution function for respective polynomial coefficients. To decide which polynomial order suffices to describe correlation structures in data, we include a method for model selection, the Bayesian Information Criterion, to the analysis. The performance of the SOMBI algorithm is tested with mock data. As illustration we also provide applications of our method to cosmological data. In particular, we present results of a correlation analysis between galaxy and AGN properties provided by the SDSS catalog with the cosmic large-scale-structure (LSS). The results indicate that the combined galaxy and LSS dataset indeed is clustered into several sub-samples of data with different average properties (for example different stellar masses or web-type classifications). The majority of data clusters appear to have a similar correlation structure between galaxy properties and the LSS. In particular we revealed a positive and linear dependency between the stellar mass, the absolute magnitude and the color of a galaxy with the corresponding cosmic density field. A remaining subset of data shows inverted correlations, which might be an artifact of non-linear redshift distortions.

Modelling galaxy clustering on small scales to tighten constraints on dark energy and modified gravity

We present a new approach to measuring cosmic expansion history and growth rate of large scale structure using the anisotropic two dimensional galaxy correlation function (2DCF) measured from data; it makes use of the empirical modeling of small-scale galaxy clustering derived from numerical simulations by Zheng et al. (2013). We validate this method using mock catalogues, before applying it to the analysis of the CMASS sample from the Sloan Digital Sky Survey Data Release 10 (DR10) of the Baryon Oscillation Spectroscopic Survey (BOSS). We find that this method enables accurate and precise measurements of cosmic expansion history and growth rate of large scale structure. Modeling the 2DCF fully including nonlinear effects and redshift space distortions (RSD) in the scale range of 16 to 144 Mpc/h, we find H(0.57)r_s(z_d)/c=0.0459 +/- 0.0006, D_A(0.57)/r_s(z_d)=9.011 +/- 0.073, and f_g(0.57)\sigma_8(0.57)=0.476 +/- 0.050, which correspond to precisions of 1.3%, 0.8%, and 10.5% respectively. We have defined r_s(z_d) to be the sound horizon at the drag epoch computed using a simple integral, f_g(z) as the growth rate at redshift z, and \sigma_8(z) as the matter power spectrum normalization on 8Mpc/h scale at z. We find that neglecting the small-scale information significantly weakens the constraints on H(z) and D_A(z), and leads to a biased estimate of f_g(z). Our results indicate that we can significantly tighten constraints on dark energy and modified gravity by reliably modeling small-scale galaxy clustering.

Understanding redshift space distortions in density-weighted peculiar velocity

Observations of the kinetic Sunyaev-Zel'dovich (kSZ) effect measure the density-weighted velocity field, a potentially powerful cosmological probe. This paper presents an analytical method to predict the power spectrum and two-point correlation function of the density-weighted velocity in redshift space, the direct observables in kSZ surveys. We show a simple relation between the density power spectrum and the density-weighted velocity power spectrum that holds for both dark matter and halos. Using this relation, we can then extend familiar perturbation expansion techniques to the kSZ power spectrum. One of the most important features of density-weighted velocity statistics in redshift space is the change in sign of the cross-correlation between the density and density-weighted velocity at mildly small scales due to nonlinear redshift space distortions. Our model can explain this characteristic feature without any free parameters. As a result, our results can precisely predict the non-linear behavior of the density-weighted velocity field in redshift space up to ∼ 30 h−1 Mpc for dark matter particles at the redshifts of z=0.0, 0.5, and 1.0.