Faits marquants 2017

3D printing, a powerful new tool for manufacturing prototypes for science

“3 Dimensional printing“, also called Additive Manufacturing, has been developing fast in recent years, especially with the marketing of turnkey professional machines which have much higher quality and reliability than their counterparts designed for the general public. Today a wide range of 3D printing processes can be used to make high precision parts, in many materials. Full text.

Tales from the Ices

When William Giauque developed cryogenics in the early 1930’s, he aimed at testing the third principle of thermodynamics, one formulation of it being : “The entropy of a perfect crystal at absolute zero is exactly equal to zero”. As nearly a century of work has shown, this statement is not precise enough, and there are nowadays experimental systems which, even very close to absolute zero, still fluctuate greatly, i.e. retain finite entropy.
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“Seeing” electrochemical growth of ultra-thin metal films

Ultra-thin metallic films have attracted considerable interest in many scientific fields, including physics, chemistry and biology. They have numerous industrial applications, in catalysis, nano-­electronics, coatings in metallurgy, surfaces of implants in medicine... The technique of grazing incidence X-Ray diffraction is well adapted for elucidating the surface structure and morphology of such films at the atomic scale. Full text.

Switching magnetic skyrmion bubbles on and off

Skyrmions were at first a theoretical concept formulated by Tony Skyrme in 1962 in the context of nuclear physics, as a model for nucleons. Technically, they are “topological solitons“ localized in space and with particle-like properties : they have quantized “topological charges“, interact via attractive and repulsive forces, and can condense into ordered phases. Full text.

A nano-trampoline to probe quantum behaviour

A phase transition is a general term for physical phenomena wherein a system transits from one state to another as a result of changing the temperature. Everyday examples are the transition from ice to water (solid to liquid) at zero degrees centigrade, and from water to vapour (liquid to gas) at 100 degrees. The temperature at which the transition takes place is called the critical point. Full text.

Spintronics at the single electron level

A single electron spin isolated in a quantum dot (a very small area in a semiconductor nanostructure) has been demonstrated to be an elementary magnetic memory useable for storing one bit of quantum information. Such a memory is very well protected from the solid state environment. Full text.

Molecular spin devices for quantum algorithms

Scrapbooks or social networks are collections of mostly unsorted data. The search for single elements in very large data volumes, i.e. for a needle in the data haystack, is extremely complex for classical computers. Classical computers switch transistors either on or off to symbolize data as ones and zeroes. Full text.

Imaging quantum dots with strain

Semiconductor “nanowires“ are long and narrow, submicron-diameter crystals of semiconducting materials. Grown from the vapour, densely packed onto a substrate, they have been under intense investigation for the last two decades, especially for their use in light emitting diodes (LEDs), photovoltaics and energy harvesting devices. Full text.

Order or disorder : How close do you look ?

When magnetic atoms are positioned on a triangular lattice, strange things can happen. When the interaction of the magnetic moments favors neighboring moments to be anti-parallel (one directed up, the other down), the three magnetic moments of a triangle cannot all be in their ideal magnetic state. Full text.

New SKID-detectors : a world below the superconducting gap

Superconductivity is a fascinating state of matter that corresponds to zero electrical resistance. It occurs in certain materials when cooled below a characteristic critical temperature Tc . From the microscopic point of view, superconductivity consists of a condensate of pairs of electrons (“Cooper pairs”) flowing without any energy dissipation. Full text.

A world map of organic semiconductors

An attractive feature of organic materials is the possibility of tailoring compounds with specific electronic properties by tuning the chemical structure of the component molecules. While this flexibility is real, new materials have traditionally been discovered through trial-and-error approaches, with no clear principle on how to predict and optimize the required characteristics. Full text.

Nanoscale nonlinear plasmonics

Integrating quantum-optics devices is one of the main challenges for the next decade especially in view of microprocessor-scale quantum computing. This requires taking experiments that are done today on an optical table and downsizing them to a few hundred nanometres, the equivalent to what was done in the past century for transistors. Full text.

Switching nanotube-molecule hybrids with light

Carbon nanotubes are one or more graphene sheets (monolayers of carbon atoms) rolled into the form of a hollow, cylindrical tube. They are 1-Dimensional electrical conductors and, by their size, they bridge the gap between small-molecule electronics and conventional semiconductor technology. Full text.

Pinching off electron edge-channels in graphene

Recent progress in techniques for microfabrication of 2-Dimensional layered materials have led to the emergence of “van der Waals“ (vdW) heterostructures. The disruptive aspect of the new assembly processes, which exploit the Van der Waals forces between atomic layers, is that the experimentalist can simply pick up 2-D crystals, put them into contact and stack them layer-by-layer, using relatively inexpensive micro-manipulation equipment. Full text.

Pinning and unpinning of charge-density waves

A charge-density wave (CDW) is a modulation of the electron density in a low-dimensional conducting solid. It appears below a critical temperature called the Peierls temperature, concomitantly with a periodic lattice distortion. Low-dimensional materials such as certain sulphides and selenides of niobium and tantalum have long been famous examples showing one-dimensional charge density waves. Full text.

Quantum plasmonics in a 2-Dimensional chiral world

Chirality, that is the lack of any mirror symmetry of a system (for example a helix) is of great importance in many fields of science especially biology and chemistry. In optics, since the pioneering work of Arago and Fresnel, it is generally linked to “optical activity“, i.e. the remarkable capability of some optical media to induce a circular birefringence and thus a difference in propagation for left and right handed circularly polarized light. Full text.

Orbital singlets indeed exist the case of Sr3Cr2O7

Below some transition temperature, the magnetic moments of atoms in a solid can arrange themselves in different structures. Namely, the moments can point in the same direction, rendering a rigid “ferromagnetic“ order. Or (as first proposed by Louis Néel in 1936) neighbouring moments can point in alternating directions, rendering a rigid “antiferromagnetic“ ordering. Full text.

Magnetic fragmentation in spin ice

In the presence of competing energies, matter tries to adapt by stabilizing novel states. In magnetism, the competition between magnetic interactions can create magnetic states different from conventional ferromagnetic or antiferromagnetic ordered states, and which remain disordered down to the limit of absolute zero of temperature. Full text.

Electron beam techniques to probe semiconductor nanowires

Semiconductor “nanowires“ are long and narrow, submicron-diameter crystals of semiconducting materials. Grown from the vapour, densely packed onto a substrate, they have been under intense investigation for the last two decades, especially for their use in light emitting diodes (LEDs), photovoltaics and energy harvesting devices. Full text.

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