Magnetic and thermal properties of 4f-3d ladder-type molecular compounds

We report on the low-temperature magnetic susceptibilities and specific heats of the isostructural spin-ladder molecular complexes L$_{2}$[M(opba)]_{3\cdot xDMSO$\cdot y$H$_{2}$O, hereafter abbreviated with L$_{2}$M$_{3}$ (where L = La, Gd, Tb, Dy, Ho and M = Cu, Zn). The results show that the Cu containing complexes (with the exception of La$_{2}$Cu$_{3}$) undergo long range magnetic order at temperatures below 2 K, and that for Gd$_{2}$Cu$_{3}$ this ordering is ferromagnetic, whereas for Tb$_{2}$Cu$_{3}$ and Dy$_{2}$Cu$_{3}$ it is probably antiferromagnetic. The susceptibilities and specific heats of Tb$_{2}$Cu$_{3}$ and Dy$_{2}$Cu$_{3}$ above $T_{C}$ have been explained by means of a model taking into account nearest as well as next-nearest neighbor magnetic interactions. We show that the intraladder L--Cu interaction is the predominant one and that it is ferromagnetic for L = Gd, Tb and Dy. For the cases of Tb, Dy and Ho containing complexes, strong crystal field effects on the magnetic and thermal properties have to be taken into account. The magnetic coupling between the (ferromagnetic) ladders is found to be very weak and is probably of dipolar origin.Comment: 13 pages, 15 figures, submitted to Phys. Rev.

Testing foundations of quantum mechanics with photons

The foundational ideas of quantum mechanics continue to give rise to counterintuitive theories and physical effects that are in conflict with a classical description of Nature. Experiments with light at the single photon level have historically been at the forefront of tests of fundamental quantum theory and new developments in photonics engineering continue to enable new experiments. Here we review recent photonic experiments to test two foundational themes in quantum mechanics: wave-particle duality, central to recent complementarity and delayed-choice experiments; and Bell nonlocality where recent theoretical and technological advances have allowed all controversial loopholes to be separately addressed in different photonics experiments.Comment: 10 pages, 5 figures, published as a Nature Physics Insight review articl

Theoretical analysis of the vanadyl pyrophosphate VO 2 P 2 O 7 31 P NMR spectra

Abstract We present a theoretical analysis of the temperature dependence of the vanadyl pyrophosphate VO 2 P 2 O 7 31 P NMR spectra. Four distinct phosphorus sites responsible for four signals are identi®ed in the crystal structure. The magnetic states of the crystal are described by two alternative models: the spin ladder and the dimer chain. Within both models, ®nite clusters with and without periodic conditions are considered. The ®t of the experimental NMR data allows us to de®ne combinations of hyper®ne coupling parameters which are found to be similar in both spin models.

Visualizing the coordination-spheres of photoexcited transition metal complexes with ultrafast hard X-rays

The concept of coordination sphere (CS) is central to the rational development of hierarchical molecular assemblies in modern chemistry. Manipulating the organization around transition metal ions with covalent and supramolecular interactions is a general strategy that underlies most synthetic protocols. Achieving similar control for photoexcited molecular complexes is necessary to advance the design of light-driven functionalities. This objective calls for monitoring the ultrafast dynamics of the primary (1-CS) and the secondary (2-CS) coordination spheres on the atomic scale, which remains to date an important experimental challenge for short-lived species. In this work, transient wide-angle scattering of hard X-rays (25 keV) is employed with state-of-the-art AIMD simulations in order to visualize the 1-CS (solute-only) and the 2-CS (solvation cage) of the photoinduced high-spin (HS) state for [Fe(bpy) 3 ] 2+ (bpy = 2,2′-bipyridine) in aqueous solution. Correlating this structural information in real-space reveals the interlacing of the two CS, which in turn explains why solvation affects the photoinduced electronic and structural dynamics in this class of complexes. More generally, these results obtained for a prominent prototypical system in ultrafast X-ray sciences demonstrate the unique perspectives offered by this technique to gain the crucial knowledge about the multiscale solvation dynamics that is currently missing for controlling the solute-solvent interactions in advanced functional nano and biomaterials employed for photoconversion

Photoswitching of the Dielectric Constant of the Spin-Crossover Complex [Fe(L)(CN)2]H2O

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Aircraft Wake Vortex Study and Characterization with 1.5 µm Fiber Doppler Lidar

International audienceFor ten years now, Onera has been developing lidar tools for wake vortex detection and studies. Since 2003, new developments based on 1.5 µM fibered laser sources have been achieved in parallel with extensive research work on the laser sources themselves.Three innovative lidars have been developed and are presented in this paper:1) A mini-lidar, based on a CW (continuous-wave) 2 W / 1.5 µM laser source, for aircraft model wake vortex characterization in a catapult facility. A self-triangulation technique allows the vortex core position to be found with 10 cm error, and the circulation error is 10 %.2) A pulsed 1.5 µM lidar, based on a 50 µJ / 15 kHz MOPA (Master Oscillator Power Amplifier) source, for lateral wake vortex monitoring at airports. The range is 400 m, the core position error is about ± 2 m and the circulation error is about 10 %.3) A pulsed 1.5 µM lidar, based on a 120 µJ / 12 kHz MOPA source, for onboard axial wake vortex detection. Ground based lidar tests at Orly airport have demonstrated wake vortex detection up to 1.2 km

Dynamic Jahn–Teller Effect in the Metastable High-Spin State of Solvated [Fe(terpy)₂]²⁺

Characterizing structural distortions in the metastable spin states of d4–d7 transition metal ion complexes is crucial to understand the nature of their bistability and eventually control their switching dynamics. In particular, the impact of the Jahn–Teller effect needs to be assessed for any electronic configuration that could be effectively degenerate, as in e.g. the high-spin (HS) manifold of highly symmetric homoleptic FeII complexes. However, capturing its manifestations remains challenging since crystallization generally alters the molecular conformations and their interconversion. With the rapid progress of ultrafast X-ray absorption spectroscopy, it is now possible to collect data with unprecedented signal-to-noise ratio, opening up for detailed structural characterization of transient species in the homogeneous solution phase. By combining the analysis of picosecond X-ray absorption spectra with DFT simulations, the structure of the photoinduced HS state is elucidated for solvated [Fe(terpy)2]2+ (terpy = 2,2′:6′,2″-terpyridine). This species can be viewed as the average 5B structure in D2 symmetry that originates from a dynamic Jahn–Teller effect in the HS manifold. These results evidence the active role played by this particular instance of vibronic coupling in the formation of the HS state for this benchmark molecule. Ultimately, correlating the interplay between intramolecular and intermolecular degrees of freedom to conformational strain and distortions in real time should contribute to the development of advanced functionalities in transition metal ion complexes