Unconventional Magnetization below 25 K in Nitrogen-doped Diamond provides hints for the existence of Superconductivity and Superparamagnetism

The magnetization of nitrogen-doped single crystalline diamond bulk samples shows unconventional field and temperature hysteresis loops at T ≲ 25 K. The results suggest the existence of superparamagnetic and superconducting regions in samples with nitrogen concentration <200 ppm. Both phases vanish at temperatures above 25 K where the samples show diamagnetic behavior similar to undoped diamond. The observation of superparamagnetism and superconductivity is attributed to the nitrogen doping and to the existence of defective regions. From particle-induced X-ray emission with ppm resolution we rule out that the main observations below 25 K are due to magnetic impurities. We investigated also the magnetic properties of ferromagnetic/high-temperature superconducting oxide bilayers. The magnetization results obtained from those bilayers show remarkable similarities to the ones in nitrogen-doped diamond

Fano interferences in environment-enabled electron capture

Interatomic Coulombic electron capture (ICEC) is an environment-assisted process in which a free electron can efficiently attach to a quantum system by transferring the excess energy of the electron capture to a neighbor ionizing it. Using the ab initio R-matrix method, we show that Fano profiles, resulting from interferences between the ICEC final states and resonant states, appear in the ICEC cross sections even at extremely large system-neighbor separations. We identify several types of resonant states depending on their decay pathways which may involve long-range electron and energy transfer. ICEC is a fundamental process and the interferences lead to substantial enhancement or decrease of the cross sections. The present investigation is therefore of general relevance in many contexts wherever electron capture in an environment takes place

Electron attachment to a proton in water by interatomic Coulombic electron capture: An <i><b>R</b></i>-matrix study

Interatomic Coulombic electron capture (ICEC) is an environment-enabled electron capture process in which a free electron can efficiently attach to a quantum system by transferring the excess energy to a neighbor thus ionizing it. Using the ab initio R-matrix method, we investigate the electron attachment to a proton in the neighborhood of a water molecule. The corresponding ICEC cross sections exhibit clear Fano profiles, resulting from interferences between the ICEC final states and resonant states. These Fano interferences, observed in the total ICEC cross sections, were discussed in our recent work on large system-neighbor separations [A. Molle et al., Phys. Rev. A 103, 012808 (2021)]. In the present study, we report on the ICEC cross sections at shorter distances which are relevant in biological and biochemical contexts. Furthermore, we investigate the partial ICEC cross sections and demonstrate that the ionization of a water molecule via ICEC is substantially different from that due to direct photoionization. Finally, we show that the distortion of the equilibrium geometry of the water molecule due to the presence of the proton influences the ICEC process

Elektronendynamik des Interatomaren Coulombischen Elektroneneinfangs in Künstlichen und Echten Atomen

Interatomic coulombic electron capture is a non-local process involving the environment-assisted attachment of a free electron with implied consequences for various systems. Starting from the established numerical model of quantum confinements in a nanowire, this dissertation sets out to deduce model-independent hypotheses for future investigations of theoretical or experimental nature and develops a generalised adaptation of the model to test whether the effective-two-electron treatment suffices to successfully capture a free electron in the experimentally motivated system of a barium (II) cation engulfed in a Bose-Einstein condensate of neutral rubidium atoms. Appearing associated to differing electronic states of the confinement region, two subprocesses can contrast in spatial preferences and resonant energies. For the investigated range of parameters, the energy levels of these associated states suggest to provide a starting point for a more comprehensive description beyond the particular parameters of an individual model. A rather simple electric dipole-dipole coupled adaptation of the model is then able to successfully show environment assisted electron attachment to a barium (II) cation aided by a surrounding cloud of ultracold rubidium atoms in typical experimental conditions

Predicting the performance of the inter-Coulombic electron capture from single-electron quantities

The probability of the inter-Coulombic electron capture (ICEC) is studied for nanowire-embedded quantum-dot pairs where electron capture in one dot leads to electron emission from the other. Previous studies pointed to an interdependence of several ICEC pathways which can enhance the ICEC reaction probability. To identify favorable criteria for such synergies in a qualitative and quantitative manner, we conducted a considerable amount of simulations scanning multiple geometrical parameters. The focus of the paper is not only to find the geometries which are most favorable to ICEC but most importantly to explain the basic principles of the ICEC probability. We have thus derived a number of energy relations among solely single-electron level energies that explain the mechanisms of the multiple reaction pathways. Among them are direct ICEC, both slowing or accelerating the outgoing electron, as well as resonance-enhanced ICEC which captures into a two-electron resonance state that decays thereafter. These pathways may apply simultaneously for just one single geometric configuration and contribute constructively leading to an enhancement of the reaction probability. Likewise some conditions are found that clearly turn down the ICEC probability to zero. The results based on single-electron relations are so general that they can as well be used to predict the ICEC probability from the electronic structure in arbitrary physical systems such as atoms or molecules

Energy transfer among electronic systems: A roadmap to ICEC and the quest for more dimensions

International audienceWhat happens when an electron scatters with a binding potential close to which there is another electronic system? One possibility is ICEC (inter-Coulombic electron capture): the binding potential takes up the electron, the neighboring system is being ionized. In numerous systematic electron dynamics calculations with antisymmetrized MCTDH (Heidelberg implementation) we have obtained a roadmap of the geometric conditions for successful ICEC. Our interpretations can straightforwardly be applied to quantum dot systems. In expanding applications at trapped ions are at hand. The other process investigated is ICD (inter-Coulombic decay). It requires a resonance state spread over two binding potentials that decays into a singly-ionized continuum state. The quest of the last years was to enhance the dimensionality of the problem. One big step towards a more-than-1d-continuum has been made in making the Coulomb interaction potential significantly more handy via multigrid POTFIT. The other was including a third electron in MCTDH

Interparticle Coulombic Decay in coupled quantum dots: enhanced energy transfer via bridge assisted mechanisms

International audienceInterparticle Coulombic Decay (ICD) is an efficient energy transfer process between two weakly interacting systems. ICD was recently proposed as the underlying fundamental mechanism for technological purposes based on quantum dot nanostructures, such as wavelength-sensitive detectors. Via ICD, an excited donor quantum dot releases its excess energy by ionizing a neighbouring acceptor dot. Here, we demonstrate that the presence of a third (ICD inactive) quantum dot can serve as a bridge between the two dots, which is shown to result in an enhancement of the efficiency of the ICD-mediated energy transfer. Furthermore, our results show that this enhancement is found to be robust against the change of the characteristics of the bridge quantum dot and particularly the depth and size. On the other hand, its relative position with respect to the donor and acceptor dots is found to foster the ICD when it is located in between the two dots. Our findings provide new insights for the development of ICD-based nanostructure technologies and particularly for rational design of three coupled quantum dots.

Structure-function relationships of CarO, the carbapenem resistance-associated outer membrane protein of Acinetobacter baumannii.

International audienceOBJECTIVES: In the context of the increasing worldwide occurrence of imipenem-resistant Acinetobacter baumannii strains, we investigated a possible porin-mediated mechanism relating to the carbapenem resistance-associated outer membrane protein, CarO. The aim of this study was to determine whether this porin may be a diffusion pathway for carbapenems in A. baumannii. METHODS: By analysing and comparing the sequences of CarO with protein databanks, we identified two major groups of sequences that we named CarOa and CarOb. We overproduced in Escherichia coli, extracted, purified by affinity chromatography and refolded in Triton X-100 rCarO from both groups. Their functional properties were investigated and compared by reconstitution in planar lipid bilayers. RESULTS: This functional study showed that rCarOa and rCarOb exhibit identical single-channel conductances (i.e. 20 pS in 1 M KCl) and similar poor cationic selectivity. Both channels were not specific towards meropenem and glutamic acid and poorly specific towards arginine, but they presented a marked specificity towards imipenem. From the calculated binding constants, we highlight that the CarOb channel was twice as specific as the CarOa channel for this antibiotic. Moreover, the CarOa channel could facilitate ornithine diffusion when the CarOb channel would not. CONCLUSIONS: We provide here the first evidence that CarO channels possess an imipenem (but not meropenem) binding site, and that their specificities depend on their primary structure. Any decrease in CarO expression would thus reduce the susceptibility of A. baumannii to this antibiotic

Channel Formation by CarO, the Carbapenem Resistance-Associated Outer Membrane Protein of Acinetobacter baumannii

It has been recently shown that resistance to both imipenem and meropenem in multidrug-resistant clinical strains of Acinetobacter baumannii is associated with the loss of a heat-modifiable 25/29-kDa outer membrane protein, called CarO. This study aimed to investigate the channel-forming properties of CarO. Mass spectrometry analyses of this protein band detected another 25-kDa protein (called Omp25), together with CarO. Both proteins presented similar physicochemical parameters (M(w) and pI). We overproduced and purified the two polypeptides as His-tagged recombinant proteins. Circular dichroism analyses demonstrated that the secondary structure of these proteins was mainly a β-strand conformation with spectra typical of porins. We studied the channel-forming properties of proteins by reconstitution into artificial lipid bilayers. In these conditions, CarO induced ion channels with a conductance value of 110 pS in 1 M KCl, whereas the Omp25 protein did not form any channels, despite its suggested porin function. The pores formed by CarO showed a slight cationic selectivity and no voltage closure. No specific imipenem binding site was found in CarO, and this protein would rather form unspecific monomeric channels