Faits marquants 2016

A quantum phase transition seen from 0 to 600 K

We are accustomed to attributing phase transitions from an ordered state towards a disordered state to a temperature increase that agitates the atoms till the order is totally broken at a critical temperature Tc. However, this type of transition can also occur at strictly zero absolute temperature, when a parameter such as pressure or magnetic field or (in the case of an alloy) the proportion x of one component is varied. Full text.

New generation of white phosphors for LED lighting

Devices based on light emitting diodes (LEDs) are a major disruptive technology expected to dominate the lighting market in the near future. The advantages of solid-state lighting sources are their energy saving (more than 50% compared to conventional fluorescent lamps) and their potential to produce high stability, long lifetime devices. Full text.

Tracking the composition of carbonblack samples from Pompeii

A better knowledge of past societies and of their degree of technological development can come from scientific analysis of archaeological remains. However, the study of residues from archaeological finds poses a series of challenges for materials science. Carbon-based materials, easy to make by burning diverse organic matter, have been used since prehistoric times as pigments for drawings and paintings and also as dyes, inks and cosmetics. Full text.

Fragmentation of magnetism

In physics as in chemistry, it is well known that matter can become ordered, as for example in a crystalline solid, when cooled to sufficiently low temperature. There also exist systems that remain disordered in the manner of a gas or a liquid, even at the lowest temperatures accessible experimentally. What is much more rare, if ever observed, is a state of matter that would be both ordered and disordered everywhere in the system, i.e. that would be both solid and liquid for example. Full text.

Microtransfer setup for assembling smart stacks

Recent, innovatory 2-Dimensional materials, such as graphene (a monolayer of carbon atoms) or transition metal di-chalcogenides (MoS2, WSe2...), can be assembled into a variety of heterostructures. These socalled “van der Waals” structures are opening up new fields for exploratory physics and applications. At the Institut NÉEL, we have developed a micro-transfer platform with a lateral mechanical-alignment precision of order one micron, which we use for making stacks of different 2D exfoliated materials. Full text.

NIKA2 : revolutionary camera for millimetre waves sees first light

An important fraction of the matter in the universe is very cold, and emits only far infrared, microwave or millimetre wave radiation. To detect cold astronomical objects, a radiotelescope’s detection instrument must be cooled to even lower temperatures, to avoid the thermal noise of the detector. NIKA 2, the second generation Neel-IRAM-KID-Array, is a dual-band millimetre-wave camera operating simultaneously at 150 and 260 GHz. Full text.

Influence of lattice vibrations on a quantum phase transition

In the vicinity of the absolute zero of temperature, all materials, except Helium, are solid. Analogous to this, the conduction electrons in certain metallic compounds can “freeze” at low temperature into a Charge- Density Wave phase : a stationary, ordered, spatial modulation of the electron density. If the temperature is raised, the charge density wave order is destroyed (it “melts”). Full text.

New multiferroics inspired by minerals

Multiferroics are materials that show both magnetism and ferroelectricity (spontaneous electric polarization) at the same time. A coupling of electric fields and magnetic fields in materials was speculated as early as 1894 by Pierre Curie. However, magnetism and ferroelectricity are generally antagonistic properties and multiferroics have long remained rather rare “creatures”. Recently, it has been understood that some specific types of magnetic order can induce ferroelectricity, and this has boosted the search for corresponding compounds. Full text.

Revealing coherence of single emitters with photonic nanostructures

Physicists usually associate coherence with macroscopic interference patterns, as observed for example in the famous experiment where light waves are passed through a double-slit. Astonishingly, interference is also generated when photons are launched one-by-one, as if they were capable of going through both slits at the same time. Full text.

Theory for organic systems : the Fiesta initiative

Nowadays, the development of efficient computer codes that exploit the basic principles of quantum mechanics for the study of condensed-matter systems requires a merging of expertise between physicists, applied mathematicians and computer scientists. Full text.

Probing the anisotropy of optical fibres by Third Harmonic Generation

An optical fibre is a fantastic tool for confining light over a huge distance, especially in modern telecommunications. We now have available a broad range of optical fibres for diverse uses. For most applications, any effect that modifies the polarization of the light propagating in the fibre must be avoided. Full text.

Quantum fragmentation and classical restoration of spins

Consider a small ferromagnetic particle — so small that it contains just a single magnetic domain — placed in a magnetic field. If one reverses the direction of the magnetic field, how fast and via what path does the magnetisation change direction ? This problem of classical physics was treated in 1948 by E. Stoner and E. Wohlfarth. Full text.

Chromium : a spin qubit with large spin to strain coupling

Quantum two level systems (“qubits”) strongly coupled to mechanical resonators can function as hybrid quantum systems with several potential applications in quantum information science. Access to a strong coupling regime, where non-classical states of a mechanical resonator are generated, could be achieved with solid state quantum bits whose energy levels have a large strain response. Full text.

The enigmatic normal state of high temperature superconductors

Superconductivity is a macroscopic quantum state characterized by the total absence of electrical resistance and the ability to fully expel an applied magnetic field. However, these fascinating properties show up only below some characteristic (critical) temperature which, for conventional superconductors, usually does not exceed a few degrees, or a few tens of degrees. Full text.

High school students discover the world of research

Each year, the Institut Néel organizes a series of one-week visits for junior high-school students. Our aim is to give these young students a glimpse of the work that people do in a CNRS laboratory, by introducing them to a selection of subjects from our research programmes. Full text.

Upgrading the Helium Liquefaction Centre

The Helium Liquefaction Centre of Grenoble, situated at the Institut NÉEL, is the largest in France. Each year, about 400 000 litres of liquid helium are distributed to CNRS and university laboratories as well as to the large European research facilities in Grenoble – the European Synchrotron Research Facility (ESRF) and the Institut Laue Langevin (ILL) neutron source. Full text.

Charge-carrier puddles in graphene

What is the spatial extent over which a localized charge perturbs the density of the free charge carriers (electrons or holes) in a two-dimensional electron gas ? In graphene – a remarkable 2D material where the charge carriers have zero mass – the capacity to screen background charges depends very strongly on the charge-carrier density. Full text.

Complex magnetism in rare-earth iridates

Research in condensed matter magnetism has mainly focused on materials incorporating elements of the 3d transition-metal series (Fe, Co…) and elements of the 4f lanthanide rare earths series (Nd, Tb, Er...). The 3d and the 4f electrons have very different magnetic properties Full text.

Kondo phase shift in quantum point-contacts

A quantum point-contact is a very small constriction in a plane of electrons, defined by gate electrodes. At temperatures near absolute zero, in addition to the well-known quantization of its conductance, this device exhibits anomalous features attributed to strong Coulomb interactions between electrons in the constriction. Full text.

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