While the LHC is still at the beginning of its life cycle, no major increases in the centre-of-mass energy are expected in the future, and the absence of apparent signs of new physics call for the development of precision tests of the Standard Model with the existing and future data.
Vector Boson Scattering (VBS) and di-Higgs production will play a crucial role in this effort, as they give direct access to the very heart of the electroweak symmetry breaking: on the one side by measuring the impact of the Higgs boson in the VBS unitarity, on the other side by investigating the self-coupling of the Higgs boson itself.

In order to develop spintronic devices, a precise control of the magnetic state in ultrathin films is necessary. Starting from the Fe/Ir interface, known to generate a large Dzyaloshinskii-Moriya interaction, we show how to obtain and tune spin spirals or magnetic skyrmions using spin-polarized scanning tunneling microscopy (SP-STM).
Since the lattice mismatch between Fe and Ir is very large, the epitaxially grown double Fe atomic layer on Ir(111) exhibits a network of dislocation lines along high-symmetry directions. These lines allow to relieve the epitaxial strain in the film and fix the propagation direction of spin spirals with a period about 1.5 nm. When atomic hydrogen is incorporated in the double layer film, the dislocation lines network disappears and is replaced by a p(2x2) hexagonal superstructure. The propagation direction of the spin spirals is thus not fixed anymore and their period increases to 3.5 nm. Furthermore, they transform into skyrmions under application of a magnetic field of 3 T whereas, this is not the case in the pristine double layer. Ab initio calculations indicate that the H atoms must be located between the two Fe layers and allow to reproduce the observed results.
Another possibility to modify the magnetic state is to add one more atomic Fe layer. As well as in the double layer film, spin spirals propagate along dislocation lines in the triple layer film. In addition, the spacing between the lines is varying over the sample surface which means that the strain relief is also not uniform. Our measurements revealed a clear correlation between the dislocation line spacing and the magnetic period. Based on a simple micromagnetic model, we attribute this observation to a modulation of the effective exchange coupling by the epitaxial strain relief.
Although the effect of strain relief was studied at low temperature, we also investigated the temperature dependence of the spin spirals. Whereas no spiral could be observed in the double layer above 150 K, the spirals are still stable in the triple layer Fe up to room temperature. Moreover, their period increases drastically and becomes 15 times larger than at 8 K. In order to explain this unexpected temperature-dependent behaviour, we propose a classical spin model based on different magnetic parameters in the three Fe layers. This model allows us to reproduce the period increase using both a mean-field and a Monte Carlo approach.
Under application of a magnetic field, the low-temperature spin spirals split up into skyrmions with a typical size about 5 nm. We demonstrate that they can reliably be written and deleted locally by the STM tip. The strong-bias polarity dependence and the linear behavior of the threshold voltage with the tip-sample distance shows that electric field plays the dominant role in the switching mechanism.

Describing three bodies moving under known mutual forces is difficult, especially in quantum mechanics. On the other hand, the two-body problem is very simple. A new method uses the two-body solution to solve this three-body problem.

We present a general approach for the solution of the three-body problem for a general interaction and apply it to the case of the Coulomb interaction. This approach is exact, simple, and fast. It makes use of integral equations derived from the consideration of the scattering properties of the system. In particular, this makes full use of the solution of the two-body problem, the interaction appearing only through the corresponding known T matrix. In the case of the Coulomb potential, we make use of a very convenient expression for the T matrix obtained by Schwinger. As a check, we apply this approach to the well-known problem of the helium atom ground state and obtain a perfect numerical agreement with the known result for the ground-state energy. The wave function is directly obtained from the corresponding solution. We expect our method to be, in particular, quite useful for the trion problem in semiconductors.

Glass films created by vapor depositing particles onto a properly prepared substrate have properties similar to those of ordinary glasses aged for thousands of years. It has been a challenge to study these glasses using computer simulations due to the long time scales involved. Here we use computer simulations to examine two aspects of vapor deposited glasses. First, we examine the role of surface mobility on the creation of ultra-stable vapor deposited glasses. We show that the surface mobility plays the same role in creating vapor deposited glasses as the bulk mobility does for glasses cooled at a constant rate. Second, we examine the melting of stable glasses. Vapor deposited glasses can melt via a front initiated at the surface, while this melting mechanism is not observed for liquid cooled glasses. We use the swap Monte Carlo algorithm to create stable glasses and examine the conditions where the glasses melt via a front versus a bulk mechanism. We also examine what controls the front velocity.

Sub-wavelength localization of single nano-emitters allows super-resolution imaging and subtle probing of spatio-temporal nano-environments [1]. Based on this general feature, I will present different types of nano-emitters used to study the complexity of the brain. Following a general introduction presenting the current state-of the art in this domain, I will introduce an original nanoparticle delivery method in the brain of live animals which made possible single quantum dot tracking in intact brain slices [2]. I will then introduce a recent strategy based on phase imaging which pushes the performance of 3D single particle tracking and 3D super-resolution microscopy deep into biological tissues [3]. Interestingly, for deep tissue imaging, single walled carbon nanotubes, which bear optical resonances in the near infrared, nanoscale dimensions and high aspect ratios, are particularly promising [4,5]. I will show that nanotubes diffusing in the brain extracellular space can be recorded at the single nanotube level. Analysis of their specific movements provides super-resolved maps of tissue architecture which can be modulated upon biochemical digestion of the brain extracellular matrix in live animals [6] or in neurodegenerative brains. If time permits, I will finally discuss the possibility to use sp3-defect functionalized nanotubes for single particle tracking [7].


[1] A. G. Godin, et al Biophys. J. 107 (2014) 1777
[2] Varela et al, Nat. Comm. 7 (2016) 10947
[3] Bon et al Nat. Meth. (2018) accepted
[4] N. Fakhri, et al Science 330, (2010) 1804.
[5] N. Danné, et al ACS Nano 5, 2, (2018) 359-364
[6] A. G. Godin, et al Nat. Nanotechnol. 12 (2017) 238
[7] N. Danné, et al submitted

Condensed He-4 is a fascinating system because it exhibits quantum properties at the macroscopic scale. The most famous of these is probably the transition of the liquid into a so called superfluid state when cooled down below 2.17 K at vapor pressure. I will present and discuss experiments investigating the metastable phases of liquid and solid He-4. Metastable solid He-4 is interesting because it is a potential candidate for a hypothetical (not yet discovered) supersolid state of matter. Metastable liquid He-4 is interesting because due to its extreme purity, it is a model system to study homogeneous cavitation. The metastable states are produced by focusing an acoustic wave in the bulk of the solid (liquid). We measure the local density within the wave thanks to an optical time-resolved interferometric method. In both metastable liquid and solid He-4, we have observed instabilities at densities which are not compatible with theoretical predictions. In the particular case of metastable liquid He-4, our density measurement of its cavitation threshold especially questions the validity of a well theoretically established equation of state of the metastable liquid. It then appears necessary to try to measure the equation of state experimentally which could be done using a stimulated Brillouin scattering technique.

Whenever one material moves against another, some energy can be lost due to adhesion hysteris and/or friction. That energy is transferred into unwanted heat, deformation, or wear reducing the material’s lifetime. A number of experimental studies have shown that polymer coatings can be efficiently used to control friction and adhesion between surfaces. Polymer coatings have properties and responsiveness that are contingent on the chemical composition, size and shape of structure, elasticity. However, they are generally suffering from major shortcomings such as lack of responsiveness selectivity and reversibility, poor environmental stability and limited understanding of the structure–function relationship, which are all critical to design reliable rules for building responsive or self-lubricating surfaces. Experimental surface forces studies of different classes of solvated polymer-bearing surfaces carried out using the surface forces apparatus and similar molecular techniques will be presented in order to elucidate the responsiveness mechanism and the structure–property relationship between polymer-coated surfaces in aqueous media. Eventhough conclusive understanding is still hampered by the difficulty of systematically controlling the grafting density, the studies suggest that the effective lubrication mechanisms involve the facility with which macromolecules under compression remain hydrated and hold a significant amount of water at the surfaces to be lubricated.

The binary Kob-Andersen (KA) Lennard-Jones mixture is the standard model for computational studies of viscous liquids and the glass transition. For very long runs the viscous KA system crystallizes, however, by phase separating into a pure A particle phase forming an FCC crystal. We present the phase diagram for KA-type mixtures showing, in particular, that the freezing temperature of the standard KA system at liquid density 1.2 is 1.028(3). At large B particle concentrations the system crystallizes into the CsCl crystal structure. The eutectic corresponding to the FCC and CsCl structures is cut-off in a narrow interval of B particle concentrations around 25% at which the PuBr 3 structure is the thermodynamically stable phase. The melting temperature’s variation with B particle concentration at two other pressures, as well as at the constant density 1.2, are predicted from the simulations using isomorph theory; interface-pinning simulations confirm these predictions. Our data demonstrate approximate identity between the melting temperature and the
onset temperature below which viscous dynamics appears.

Introduction to semimagnetic semiconductors (diluted magnetic semiconductors, DMS) is given. Semimagnetic properties of ZnMnTe are described, as obtained by parallel studies of magneto-reflectivity (MR) and magneto-photoluminescence (MPL). Properties of MR resonances are presented and explained. Spin-polarized MPL spectra are shown, exhibiting simultaneous presence of paramagnetic Mn-ions, excitons and donor- acceptor pairs. A coefficient of MPL circular light polarization P(Mn) is introduced and it is demonstrated that it as an important quantity characterizing a semimagnetic material. A relation between the Zeeman shifts of exciton transitions due to exchange interaction with mobile carriers and Mn-ions and P(Mn) due to internal recombination of Mn-ions is revealed. An enhancement of binding energies with increasing magnetic field for excitons localized by potential fluctuations is demonstrated and explained. Simultaneous presence of Mn paramagnetic ions and residual nonmagnetic impurities in ZnMnTe provides for a rich physical picture.