The majority of short gamma-ray bursts (SGRBs) are thought to originate from the merger of compact binary systems collapsing directly to form a black hole. However, it has been proposed that both ...SGRBs and long gamma-ray bursts (LGRBs) may, on rare occasions, form an unstable millisecond pulsar (magnetar) prior to final collapse. GRB 090515, detected by the Swift satellite was extremely short, with a T90 of 0.036 ± 0.016 s, and had a very low fluence of 2 × 10−8 erg cm−2 and faint optical afterglow. Despite this, the 0.3–10 keV flux in the first 200 s was the highest observed for an SGRB by the Swift X-ray Telescope (XRT). The X-ray light curve showed an unusual plateau and steep decay, becoming undetectable after ∼500 s. This behaviour is similar to that observed in some long bursts proposed to have magnetars contributing to their emission. In this paper, we present the Swift observations of GRB 090515 and compare it to other gamma-ray bursts (GRBs) in the Swift sample. Additionally, we present optical observations from Gemini, which detected an afterglow of magnitude 26.4 ± 0.1 at T+ 1.7 h after the burst. We discuss potential causes of the unusual 0.3–10 keV emission and suggest it might be energy injection from an unstable millisecond pulsar. Using the duration and flux of the plateau of GRB 090515, we place constraints on the millisecond pulsar spin period and magnetic field.
Two-dimensional transition metal dichalcogenides (TMDs) provide a unique possibility to generate and read-out excitonic valley coherence using linearly polarized light, opening the way to valley ...information transfer between distant systems. However, these excitons have short lifetimes (ps) and efficiently lose their valley coherence via the electron-hole exchange interaction. Here, we show that control of these processes can be gained by embedding a monolayer of WSe
in an optical microcavity, forming part-light-part-matter exciton-polaritons. We demonstrate optical initialization of valley coherent polariton populations, exhibiting luminescence with a linear polarization degree up to 3 times higher than displayed by bare excitons. We utilize an external magnetic field alongside selective exciton-cavity-mode detuning to control the polariton valley pseudospin vector rotation, which reaches 45° at B = 8 T. This work provides unique insight into the decoherence mechanisms in TMDs and demonstrates the potential for engineering the valley pseudospin dynamics in monolayer semiconductors embedded in photonic structures.
Abstract
Semiconducting ferromagnet-nonmagnet interfaces in van der Waals heterostructures present a unique opportunity to investigate magnetic proximity interactions dependent upon a multitude of ...phenomena including valley and layer pseudospins, moiré periodicity, or exceptionally strong Coulomb binding. Here, we report a charge-state dependency of the magnetic proximity effects between MoSe
2
and CrBr
3
in photoluminescence, whereby the valley polarization of the MoSe
2
trion state conforms closely to the local CrBr
3
magnetization, while the neutral exciton state remains insensitive to the ferromagnet. We attribute this to spin-dependent interlayer charge transfer occurring on timescales between the exciton and trion radiative lifetimes. Going further, we uncover by both the magneto-optical Kerr effect and photoluminescence a domain-like spatial topography of contrasting valley polarization, which we infer to be labyrinthine or otherwise highly intricate, with features smaller than 400 nm corresponding to our optical resolution. Our findings offer a unique insight into the interplay between short-lived valley excitons and spin-dependent interlayer tunneling, while also highlighting MoSe
2
as a promising candidate to optically interface with exotic spin textures in van der Waals structures.
Abstract
Monolayer transition metal dichalcogenides (TMDs) hold great promise for future information processing applications utilizing a combination of electron spin and valley pseudospin. This ...unique spin system has led to observation of the valley Zeeman effect in neutral and charged excitonic resonances under applied magnetic fields. However, reported values of the trion valley Zeeman splitting remain highly inconsistent across studies. Here, we utilize high quality hBN encapsulated monolayer WSe
2
to enable simultaneous measurement of both intervalley and intravalley trion photoluminescence. We find the valley Zeeman splitting of each trion state to be describable only by a combination of three distinct g-factors, one arising from the exciton-like valley Zeeman effect, the other two, trion specific, g-factors associated with recoil of the excess electron. This complex picture goes significantly beyond the valley Zeeman effect reported for neutral excitons, and eliminates the ambiguity surrounding the magneto-optical response of trions in tungsten based TMD monolayers.
Long-duration gamma-ray bursts (GRBs) are thought to be produced by the core-collapse of a rapidly rotating massive star. This event generates a highly relativistic jet and prompt gamma-ray and X-ray ...emission arises from internal shocks in the jet or magnetized outflows. If the stellar core does not immediately collapse to a black hole, it may form an unstable, highly magnetized millisecond pulsar or magnetar. As it spins down, the magnetar would inject energy into the jet causing a distinctive bump in the GRB light curve where the emission becomes fairly constant followed by a steep decay when the magnetar collapses. We assume that the collapse of a massive star to a magnetar can launch the initial jet. By automatically fitting the X-ray light curves of all GRBs observed by the Swift satellite, we identified a subset of bursts which have a feature in their light curves which we call an internal plateau – unusually constant emission followed by a steep decay – which may be powered by a magnetar. We use the duration and luminosity of this internal plateau to place limits on the magnetar spin period and magnetic field strength, and find that they are consistent with the most extreme predicted values for magnetars.
The South China Sea (SCS) is recognised as a global hotspot for plastic pollution. We review available field studies and identify a significant lack of data needed to construct a simple mass balance ...box model for plastic pollution in the SCS. Fundamental information on plastic mass input, transfer and sink terms are simply not available. Also unknown are the rates of accumulation in different environments, the dispersal pathways of plastic particles of different density, the residence times of plastic in the water column and the rate at which macroplastics are transformed into microplastics in different environments. Filling these information gaps is critical for states to determine adequate response measures, including developing and tracking impact of policies to deal with the problem of plastic pollution in the SCS.
•Source and sink terms for plastic entering the South China Sea are assessed.•Data are insufficient to build a mass balance box model.•Knowledge gaps include sources, sinks, pathways and impacts of plastic pollution.•A precautionary approach is recommended to guide immediate response options.
Nonsymmetric substitution of salen (1 R1,R2 ) and reduced salen (2 R1,R2 ) CuII–phenoxyl complexes with a combination of - t Bu, -S i Pr, and -OMe substituents leads to dramatic differences in their ...redox and spectroscopic properties, providing insight into the influence of the cysteine-modified tyrosine cofactor in the enzyme galactose oxidase (GO). Using a modified Marcus–Hush analysis, the oxidized copper complexes are characterized as Class II mixed-valent due to the electronic differentiation between the two substituted phenolates. Sulfur K-edge X-ray absorption spectroscopy (XAS) assesses the degree of radical delocalization onto the single sulfur atom of nonsymmetric 1 t Bu,SMe+ at 7%, consistent with other spectroscopic and electrochemical results that suggest preferential oxidation of the -SMe bearing phenolate. Estimates of the thermodynamic free-energy difference between the two localized states (ΔG o) and reorganizational energies (λR1R2 ) of 1 R1,R2 + and 2 R1,R2 + lead to accurate predictions of the spectroscopically observed IVCT transition energies. Application of the modified Marcus–Hush analysis to GO using parameters determined for 2 R1,R2 + predicts a νmax of ∼13600 cm–1, well within the energy range of the broad Vis–NIR band displayed by the enzyme.
We investigate the nonlinear mechanical properties of GaAs nanowires with anisotropic cross-section. Fundamental and second order flexural modes are studied using laser interferometry with good ...agreement found between experiment and theory describing the nonlinear response under mechanical excitation. In particular, we demonstrate that the sign of the nonlinear coupling between orthogonal modes is dependent on the cross-section aspect ratio. The findings are of interest for applications such as amplitude to frequency conversion and vectorial force sensing.
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