The Strasbourg Institute of Material Physics and Chemistry (IPCMS—French: Institut de Physique et Chimie des Matériaux de Strasbourg) is a joint research unit between the French National Center for Scientific Research (CNRS) and the University of Strasbourg. It was founded in 1987 and is located in the district of Cronenbourg in Strasbourg, France.
Superradiant phase transitions (SRPTs), characterized by photon condensation and macroscopic matter polarization, are forbidden in equilibrium for homogeneous fields by no-go theorems. Here, we show that Floquet driving can circumvent this constraint in a Landau polariton system consisting of a two-dimensional electron gas coupled to a terahertz cavity in a DC magnetic field. An off-resonant AC magnetic field modulates the cyclotron frequency and light–matter coupling strength while leaving the diamagnetic term unchanged, generating an additional DC coupling contribution. This drives the system across a critical threshold into a superradiant phase, characterized by photon condensation and Landau-level polarization in the ground state of the Floquet Hamiltonian. This quasiequilibrium approach offers a route to SRPTs distinct from driven-dissipative schemes.
Using propagating spin wave spectroscopy we measure the spin wave Doppler shift in patterned MgO/ Co 2 MnSi / MgO thin films and determine the degree of spin polarization of the electric current. Our measurements reveal that the current is fully spin polarized in the devices. This shows that the half-metallic character of the electron band structure translates into a fully spin polarized current flowing across the patterned films. Additionally, we measure a current-induced change of the spin-wave attenuation from which we estimate the nonadiabatic spin-transfer-torque parameter.
Defect engineering and structure‐property relationship understanding in methylammonium lead iodide (MAPI) hybrid perovskites (HPs) attract significant scientific interest, as synthesis‐related defects may strongly influence intrinsic properties. We have explored a green solvent‐free synthesis—mechanosynthesis—leading to large quantities of MAPI powder with tuneable defect density suitable to study MAPI as an electromagnetic wave absorbing (EMWA) material. A dielectric loss enhancement was revealed at 11.4 GHz (X‐band) for 4 h‐ground MAPI powders (MAPI4h), compared to 30 min‐ground powders (MAPI30) when the particle size was <20 μm. MAPI powders display a fractal microstructure with agglomerates of clusters of (nano)grains (≈80 nm for MAPI4h), consisting further of oriented smaller nanograin (5–10 nm) clusters. A strong reabsorption in smaller particles was evidenced due to a surface‐defective layer. MAPI4h was shown to display a more surface‐defective layer with a higher defect density gradient from surface to (nano)grains core and unique open defects different from those in solution‐processed MAPI. These vacancy‐type surface defects would enhance dipole polarization by stabilizing methylammonium dipoles, thereby increasing permittivity. The improved dispersion of MAPI particles (<20 μm) in polymeric matrixes enhanced the surface effects and effective interactions with electromagnetic waves. This study demonstrated the potential of this green synthesis for producing large amount of HPs and tuning defects, opening new avenues for HPs EMWA application.
