Transition énergétique

We demonstrate the existence of the spin-nematic interactions in an easy-plane type antiferromagnet Ba₂CoGe₂O₇ by exploring the magnetic anisotropy and spin dynamics. The combination of neutron scattering and magnetic susceptibility measurements reveals that the origin of the in-plane anisotropy is an antiferro-type interaction of the spin-nematic operator. The relation between the nematic operator and the electric polarization in the ligand symmetry of this compound is presented. The introduction of the spin-nematic interaction is useful to understand the physics of spin and electric dipole in multiferroic compounds.

The true oxidation state of formally ‘H?^-’ ions incorporated in an oxide host is frequently discussed in connection with chemical shifts of ¹H nuclear magnetic resonance spectroscopy, as they can exhibit values typically attributed to H⁺. Here we systematically investigate the link between geometrical structure and chemical shift of H^- ?ions in an oxide host, mayenite, with a combination of experimental and ab initio approaches, in an attempt to resolve this issue.

Researchers from ETH Zurich and the Paul Scherrer Institute PSI demonstrate how the magnetic structure can be altered quickly in novel materials. The effect could be used in efficient hard drives of the future.

Researchers from the Paul Scherrer Institute PSI and ETH Zurich have now changed the magnetic arrangement in a material much faster than is possible with today’s hard drives. The researchers used a new technique where an electric field triggers these changes, in contrast to the magnetic fields commonly used in consumer devices.

High-temperature superconductivity appears as a consequence of doping charge carriers into an undoped parent compound exhibiting antiferromagnetic order; therefore, ground-state properties of the parent compound are highly relevant to the superconducting state. On the basis of this logic, spin fluctuations have been considered as the origin of pairing of the superconducting electrons in the cuprates.

Studying the magnetization of individual iron (Fe) nanoparticles by magnetic spectromicroscopy reveals that superparamagnetic (SPM) and ferromagnetic blocked (FM) nanoparticles can coexist in the investigated size range of 8-20 nm.

The origin of the pseudogap and its relationship with superconductivity in the cuprates remains vague. In particular, the interplay between the pseudogap and magnetism is mysterious. Recent low-temperature angle-resolved photoemission spectroscopy (ARPES) experiments on the underdoped cuprate superconductors indicate the presence of a fully gapped Fermi surface (FS); even in the antiferromagnetic phase.

The quantum spin-liquid compound (C₄H₁₂N₂)Cu₂Cl₆ is studied by muon spin relaxation under hydrostatic pressures up to 23.6 kbar. At low temperatures, pressure-induced incommensurate magnetic order is detected beyond a quantum critical point at P_c ∼ 4.3 kbar. An additional phase transition to a different ordered phase is observed at P₁ ∼ 13.4 kbar. The data indicate that the high-pressure phase may be a commensurate one. The established (P-T) phase diagram reveals the corresponding pressure-induced multicritical point at P₁, T₁ = 2.0 K.

We investigate 'hot' regions with anomalous high field dissipation in bulk niobium superconducting radio frequency cavities for particle accelerators by using low energy muon spin rotation (LE-μSR) on corresponding cavity cutouts. We demonstrate that superconducting properties at the hot region are well described by the non-local Pippard/BCS model for niobium in the clean limit with a London penetration depth λ_L=23+/-2 nm . In contrast, a cutout sample from the 120C baked cavity shows a much larger λ>100nm and a depth dependent mean free path, likely due to gradient in vacancy concentration. We suggest that these vacancies can efficiently trap hydrogen and hence prevent the formation of hydrides responsible for rf losses in hot regions.

The electronic structure of a La₂Ti₂O₇-layered perovskite thin film was determined by resonant inelastic X-ray scattering (RIXS) measurements and FEFF calculations. It was found that the empty Ti and La d-band states dominate the conduction band of the structure, whereas the top edge of the valence band is mainly composed of filled O-p states. Furthermore, there is a pronounced overlap between occupied La-p states and O-s states, which are located deeper in the valence band.

Researchers at PSI reported a demonstration of X-ray tomography with an unmatched isotropic 3D resolution of 16 nm in Scientific Reports. The measurement was performed at the cSAXS beamline at the Swiss Light Source using a prototype instrument of the OMNY (tOMography Nano crYo) project. Whereas this prototype measures at room temperature and atmospheric pressure, the OMNY system, to be commissioned later this year, will provide a cryogenic sample environment in ultra-high vacuum without compromising imaging capabilities. The researchers believe that such a combination of advanced imaging with state-of-the-art instrumentation is a promising path to fill the resolution gap between electron microscopy and X-ray imaging, also in case of radiation-sensitive materials such as polymer structures and biological systems.

Novel carbon materials are promising candidates for light and robust low-cost materials of the future. Understanding their mechanical properties benefits from highly resolved three-dimensional (3D) maps of their porosity and density fluctuations in uninterrupted representative volumes, but these are difficult to obtain with conventional imaging methods.

Phase inhomogeneity of otherwise chemically homogenous electronic systems is an essential ingredient leading to fascinating functional properties, such as high-T_c superconductivity in cuprates, colossal magnetoresistance in manganites and giant electrostriction in relaxors. In these materials distinct phases compete and can coexist owing to intertwined ordered parameters. Charge degrees of freedom play a fundamental role, although phase-separated ground states have been envisioned theoretically also for pure spin systems with geometrical frustration that serves as a source of phase competition.

Tomographic microscopy has become an invaluable imaging method in both life and materials sciences. Oftentimes, high resolving power is required simultaneously with the ability to characterize large, statistically representative sample volumes. To this task, researchers at the Paul Scherrer Institut have established ptychographic computed tomography.

Topological insulators are the key to future spintronics technologies. EPFL scientists have unraveled how these strange materials work, overcoming one of the biggest obstacles on the way to next-generation applications.Read the full story