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Spin-orbit coupling in scattering of very low-energy spin-polarized electrons from Co film by (e,2e) spectroscopy
摘要： Energy and momentum distributions of correlated electron pairs excited by very low energy (9–30 eV) spin-polarized electrons from a thin Co film on a single crystal of W(110) were detected and analysed. Polarization of the incident electrons was perpendicular to the scattering plane. Spin effects are presented in form of asymmetry A = (I+ ? I?)/(I+ + I?), where I+ and I? are two-electron spectra recorded with incident electrons polarization parallel or anti-parallel to the magnetization of the sample, respectively. Performing measurements at two opposite magnetizations of the sample and assuming negligible interference between spin orbit coupling and exchange effect in scattering, two component of asymmetry can be extracted, namely a spin-orbit asymmetry ASO and an exchange asymmetry Aex. The spin-orbit component of the scattering asymmetry was analysed as a function of the primary energy. Contrary to normal expectations the value of spin-orbit asymmetry decreases with increase of the primary energy in the energy range from 9 to 30 eV.
关键词： Correlated electron pairs,Electron exchange,Asymmetry,Cobalt film,Spin-orbit
更新于2025-09-23 15:23:52
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Thin Films
摘要： We demonstrate how to extract the material-dependent spin-torque efficiency (ξ) and asymmetry (λ) from the field-current nucleation boundaries of magnetic droplet solitons in orthogonal nano-contact spin-torque oscillators with Cox(Ni80Fe20)1?x, (x = 0 ? 1), fixed layers. As the perpendicular component of the fixed-layer magnetization plays a central role in governing droplet nucleation, the nucleation boundaries exhibit monotonic shifts towards higher perpendicular magnetic fields when the fixed-layer magnetization μ0Ms,p is tuned from 1.04 to 1.7 T. We then extract ξ and λ from fits to the nucleation boundaries and find that while ξ does not vary with composition, λ increases from 1.5 to 3 with increasing Co content. The analysis of droplet nucleation boundaries is hence a useful tool for the systematic study of both ξ and λ as functions of material composition.
关键词： Cox(Ni80Fe20)1?x,magnetic droplet solitons,spin-torque asymmetry,spin-torque efficiency,nano-contact spin-torque oscillators
更新于2025-09-23 15:21:21
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Normal Value Ranges for Central Retinal Thickness Asymmetry in Healthy Caucasian Adults Measured by SPECTRALIS SD-OCT Posterior Pole Asymmetry Analysis
摘要： PURPOSE. To determine the normal variation in central retinal thickness asymmetry in healthy Caucasian adults using the posterior pole asymmetry analysis (PPAA) of a SPECTRALIS spectral-domain optical coherence tomography (SD-OCT) device. METHODS. Healthy Caucasian individuals aged between 18 and 45 years with a visual acuity of minimum 20/20 and a spherical equivalent between (cid:2)1.5 and t1.5 diopters were recruited. Retinal thickness and retinal nerve ?ber layer thickness (RNFL) were using measured SPECTRALIS SD-OCT. Inter- and intraocular differences in central retinal thickness were calculated using the PPAA. The association between age, sex, and interocular asymmetry was evaluated by a linear model with Gaussian correlation structure. RESULTS. A total of 105 individuals, 30 men and 75 women, were studied. The mean age 6 SD was 28.8 6 7.87 years. The grand mean interocular retinal thickness asymmetry was 5.6 lm (95% con?dence interval [CI]: 4.6–6.5) and the grand mean intraocular retinal thickness asymmetry was 8.3 lm (95% CI: 6.8–9.9) in the right eye and 8.4 lm (95% CI: 6.7–10.0) in the left eye. The highest local asymmetries were found in the nasal corners of macula were the posterior pole thickness map overlaps the temporal vascular arches. A slight general age and sex effect on the mean interocular retinal thickness asymmetry was found to be respectively 0.04 lm/year (95% CI: 0.02–0.06 lm) and 0.54 lm (95% CI: 0.19–0.88 lm) for men compared with women. CONCLUSIONS. Statistically signi?cant physiological asymmetries in inter- and intraocular central retinal thickness exist. This must be considered when early signs of glaucoma or other pathologies are evaluated based on the retinal thickness asymmetry.
关键词： glaucoma posterior segment,normal value ranges for retinal thickness asymmetry,posterior pole retinal thickness asymmetry analysis
更新于2025-09-23 15:21:01
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Axisymmetric and Asymmetric Naphthalene-Bisthienothiophene Based Nonfullerene Acceptors: on Constitutional Isomerization and Photovoltaic Performance
摘要： Two pairs of constitutional isomers of fused-octacyclic nonfullerene acceptors (NFAs) based on a naphthalene-bisthienothiophene core with or without fluorination at the ending groups have been developed. Compared with the axisymmetric NFAs N66-IC and N66-2FIC with two six-member-ring bridges, their asymmetric constitutional isomers N65-IC and N65-2FIC both with one six-member-ring bridge and one five-member-ring bridge exhibit remarkable red-shifted absorption, higher crystallinity, and slightly down-shifted LUMO energy levels. Organic solar cells based on PBDB-T-2F:N65-2FIC achieved a promising power conversion efficiency of 10.19%, which is three times higher than that of its counterpart PBDB-T-2F:N66-2FIC cell (3.46%). While being blended with PBDB-T as the donor material, the asymmetric acceptor analogue N65-IC based solar cell pronounces a PCE of 9.03%, being significantly improved from that of 5.45% for the PBDB-T:N66-IC based cell, which is in consistency with the results from those cells from their both fluorinated donor and acceptor counterparts. Design rules on either both fluorinated, both non-fluorinated, or cross-combined donor/acceptors for device fabrication has been explored. In addition, PBDB-T-2F:N65-2FIC possesses very promising device stability with 85% of its initial PCE after an exposure time of 1500 h under one sun illumination, which is meaningful for their future commercial devices.
关键词： isomerization,naphthalene,organic solar cells,nonfullerene acceptors,asymmetry,axisymmetry
更新于2025-09-23 15:21:01
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Asymmetry flip in angle-resolved photoelectron spectra of rare gas atoms by intense circularly polarized few-cycle pulses
摘要： We examine the phenomenon of the flip in the asymmetry in the emission direction of photoelectrons from rare gas atoms upon the ionization by a circularly polarized few-cycle laser field, and derive an analytical formula representing the photoelectron kinetic energy at which the asymmetry flip occurs based on the semiclassical tunnel ionization theory. We show that the energy at which the asymmetry flip occurs varies sensitively to the duration of few-cycle laser pulses and propose that the pulse duration can be determined experimentally using this analytical formula for the asymmetry flip energy.
关键词： asymmetry flip,photoelectron spectra,rare gas atoms,circularly polarized few-cycle pulses
更新于2025-09-23 15:21:01
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Estimation of the Rashba Strength from Second Harmonic Generation in 2D and 3D Hybrid Organic-Inorganic Perovskites
摘要： The Rashba e?ect (RE), caused by concurrent spin-orbit coupling and structural inversion asymmetry (SIA), has been invoked to explain outstanding optoelectronic properties of hybrid organic inorganic perovskites (HOIPs). The SIA in HOIPs also manifests itself in second harmonic generation (SHG). Here we establish a quantitative relation between the RE strength and the low-frequency SHG value in 2D and 3D HOIPs using a newly developed e?ective-mass model. The calculated SHG, which exhibits one- and two-photon resonances between the valence and conduction bands, approaches a ?nite value at low frequencies. Using the measured SHG values in literature, the estimated RE strength is 10?3 eV?A for 3D CH3NH3PbI3 and 4 × 10?2 eV?A for 2D (C4H9NH3)2PbI4. Our results facilitate a simple and reliable determination of the RE strength of 2D and 3D HOIPs and help quantify the impact of RE on various properties in HOIPs.
关键词： second harmonic generation,Rashba effect,hybrid organic-inorganic perovskites,structural inversion asymmetry,spin-orbit coupling
更新于2025-09-23 15:21:01
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Asymmetry of Retinopathy of Prematurity Border in the Telemedicine Approaches to Evaluating Acute-Phase Retinopathy of Prematurity Study
摘要： Purpose: To measure the location of the retinopathy of prematurity (ROP) border in a sample of premature infants who developed ROP and determine location for predicting subsequent development of referral-warranted ROP (RW-ROP, defined as Stage 3 ROP, zone I ROP, or plus disease) or treated ROP. Design: Secondary analysis of data from an observational cohort study, The Telemedicine Approaches to Evaluating Acute-Phase Retinopathy of Prematurity (e-ROP) study. Subjects: Infants with birth weight (BW) less than 1251g with at least one exam and image session at ≤34 weeks postmenstrual age (PMA) with ROP not meeting RW-ROP, and at least one subsequent exam at ≥36 weeks PMA. Methods: The 5-image set from the first imaging session for each eligible eye was mosaicked, and measurements of the ROP border in each mosaicked image were made using Image J. Measurements were compared among 3 groups of eyes with ROP: (1) never developed RW-ROP or received treatment, (2) developed RW-ROP but did not receive treatment, and (3) received treatment; using analysis of variance and linear trend tests that accounted for the inter-eye correlation. Main outcome measures: RW-ROP, treated ROP Results: 317 eyes from 217 infants with mean BW 755g, mean GA 25 weeks, and mean PMA 33 weeks at first exam met study criteria. Of 211 (66.6%) eyes with sufficient quality images for grading, 147 (69.7%) did not develop RW-ROP or receive treatment, 36 (17.1%) developed RW-ROP not requiring treatment, and 28 (13.3%) received treatment for ROP. Among all eyes, the disc-to-ROP border distance followed a consistent pattern, with nasal < inferior < superior < temporal. Eyes that developed RW-ROP or underwent treatment had significantly shorter nasal and temporal disc-to-ROP border distances and smaller areas of retina within the ROP border. In multivariate analysis adjusted by BW and GA, nasal ROP border distance was a significant predictor of developing treated ROP (OR=0.86 for every 10 pixel increase in distance, p=0.002). Conclusions: ROP is located asymmetrically around the optic disc and is closest to the optic disc nasally. Location of ROP nasally at first imaging is a significant predictor of developing treated ROP.
关键词： retinopathy of prematurity,ROP,asymmetry,telemedicine,optic disc
更新于2025-09-23 15:21:01
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Asymmetric photoelectron emission from chiral molecules using a high repetition rate laser
摘要： In the chiro-optical phenomenon known as photoelectron circular dichroism, the angular distribution of electrons ionized from chiral molecules by circularly polarized light pulses has been found to be anti-symmetric with respect to the direction of the light propagation. To study this phenomenon, chiral molecules were multiphoton ionized with a femtosecond laser in our laboratory. Using a simple stereo-detection setup, direct measurements of the asymmetry for the exemplar aromatic chiral molecule 1-phenylethanol were made using 260 nm pulses produced at a rate of 1 MHz. It was found that the asymmetry had a linear dependence on Stokes’ S3 parameter indicating that the photoelectron circular dichroism is due to a single photon process from the excited state of the molecule. This is in contrast to previous and new results for camphor where a more complex dependence on S3 suggested that selective excitation of molecules with certain orientations was influential.
关键词： photoelectron circular dichroism,circularly polarized light,asymmetry,Stokes’ S3 parameter,chiral molecules
更新于2025-09-23 15:19:57
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Effects of site asymmetry and valley mixing on Hofstadter-type spectra of bilayer graphene in a square-scatter array potential
摘要： Under a magnetic field perpendicular to an monolayer graphene, the existence of a two-dimensional periodic scatter array can not only mix Landau levels of the same valley for displaying split electron-hole Hofstadter-type energy spectra, but also couple two sets of Landau subbands from different valleys in a bilayer graphene. Such a valley mixing effect with a strong scattering strength has been found observable and studied thoroughly in this paper by using a Bloch-wave expansion approach and a projected 2 × 2 effective Hamiltonian including interlayer coupling and asymmetrical on-site energies due to a vertically-applied electric field. For bilayer graphene, we find two important characteristics, i.e., mixing and interference of intervalley scatterings in the presence of a scatter array, as well as a perpendicular-field induced site-energy asymmetry which deforms severely or even destroy completely the Hofstadter-type band structures due to the dependence of Bloch-wave expansion coefficients on the applied electric field.
关键词： bilayer graphene,valley mixing,Hofstadter spectrum,site asymmetry,scatter array potential
更新于2025-09-19 17:15:36
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High-current density and high-asymmetry MIIM diode based on oxygen-non-stoichiometry controlled homointerface structure for optical rectenna
摘要： optical rectennas are expected to be applied as power sources for energy harvesting because they can convert a wide range of electromagnetic waves, from visible light to infrared. the critical element in these systems is a diode, which can respond to the changes in electrical polarity in the optical frequency. By considering trade-off relationship between current density and asymmetry of IV characteristic, we reveal the efficiency limitations of MIM diodes for the optical rectenna and suggest a novel tunnel diode using a double insulator with an oxygen-non-stoichiometry controlled homointerface structure (Mox/ Mox?y). A double-insulator diode composed of pt/tio2/tio1.4/ti, in which a natural oxide layer of tio1.4 is formed by annealing under atmosphere. The diode has as high-current-density of 4.6 × 106 A/m2, which is 400 times higher than the theoretical one obtained using Pt/TiO2/ti MiM diodes. in addition, a high-asymmetry of 7.3 is realized simultaneously. These are expected to increase the optical rectenna efficiency by more than 1,000 times, compared to the state-of-the art system. Further, by optimizing the thickness of the double insulator layer, it is demonstrated that this diode can attain a current density of 108 A/m2 and asymmetry of 9.0, which are expected to increase the optical rectenna efficiency by 10,000.
关键词： optical rectenna,oxygen-non-stoichiometry controlled homointerface structure,high-asymmetry,high-current density,MIIM diode
更新于2025-09-19 17:13:59