Intense light-field application to solids produces enormous/ultrafast non-linear phenomena such as high-harmonic generations 1, 2 and attosecond charge dynamics 3, 4 . They are distinct from conventional photonics. However, main targets have been limited to insulators and semiconductors, although theoretical approaches have been made also for correlated metals and superconductors 5 . Here, in a layered organic superconductor, a non-linear charge oscillation driven by a nearly single-cycle strong electric field of >10 megavolts /cm is observed as a stimulated emission. The charge oscillation is different from a linear response and ascribed to a polar charge oscillation with a period of 6 fs. This non-linear polar charge oscillation is enhanced by critical fluctuations near a superconducting transition temperature and a critical end point of first order Mott transitions. Its observation on an ultrafast timescale of 10 fs clarifies that the Coulomb repulsion plays an essential role in superconductivity of organic superconductors. Supplementary information forNonlinear charge oscillation driven by a single-cycle light field in an organic superconductor

Polarization selectivity of light-field-induced charge localization was investigated in an organic metal a-(BEDT-TTF)2I3 with a triangular lattice. Dependences of transient reflectivity spectra on polarizations of the 7-fs pump and probe lights indicate that a short-range charge order (CO) is efficiently induced from the metallic phase for the pump polarization perpendicular to the 1010-type CO axis. Numerical solution of a time-dependent Schrödinger equation clarified that the 1010-CO is induced by field-induced re-distribution of charges cooperating with competing inter-site Coulomb repulsions in the triangular lattice.

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In this work, Cr diffused Sm 2 Fe 17 N x core-shell magnetic powders were prepared by reduction-diffusion (RD) process. Sm 2 Fe 17 coarse, Cr 2 O 3 and Sm 2 O 3 fine powders were pulverized and mixed by ball milling, and the mixed powder was heat treated following Ca addition. Cr can diffuse into Sm 2 Fe 17 powder above 875°C in RD process, and the diffusion distance of Cr increased with increase in RD temperature. Cr diffusion distance into Sm 2 Fe 17 powder was about 1.1-1.2 μm under RD temperature at 875°C for 1.5 h, and the Cr-diffused Sm-Fe core-shell fine powder was obtained. After nitriding and washing, Cr-diffused Sm-Fe-N fine core-shell powder was successfully obtained, and the coercivity and saturation magnetization of the core-shell powder was 855 kA·m −1 and 122 Am 2 ·kg −1 , respectively. The saturation magnetization was higher than non-core-shell Sm-Fe-Cr-N powder.

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