The B20 magnets with the Dzyaloshinskii-Moriya (D-M) interaction exhibit spin helix and Skyrmion spin textures unattainable in traditional Heisenberg ferromagnets. We have determined the intrinsic resistivity of the spin helix, which is a macroscopic
Bloch domain wall, in B20 (Fe-Co)Si magnets. We found a universal resistance ratio of gamma = 1.35 with current parallel and perpendicular to the helix, independent of composition and temperature. This gamma value is much smaller than 3, the well-known minimum value for domain wall resistivity in traditional ferromagnets, due to the significant spin-orbit coupling in the B20 magnets.
The B20 chiral magnets with broken inversion symmetry and C4 rotation symmetry have attracted much attention. The broken inversion symmetry leads to the Dzyaloshinskii-Moriya that gives rise to the helical and Skyrmion states. We report the unusual m
agnetoresistance (MR) of B20 chiral magnet Fe0.85Co0.15Si that directly reveals the broken C4 rotation symmetry. We present a microscopic theory, a minimal theory with two spin-orbit terms, that satisfies all the symmetry requirements and accounts for the transport experiments.
The superconducting gap in FeAs-based superconductor SmFeAs(O1-xFx) (x = 0.15 and 0.30) and the temperature dependence of the sample with x = 0.15 have been measured by Andreev reflection spectroscopy. The intrinsic superconducting gap is independent
of contacts while many other gap-like features vary appreciably for different contacts. The determined gap value of 2D = 13.34 +/-0.47 meV for SmFeAs(O0.85F0.15) gives 2D/kBTC = 3.68, close to the BCS prediction of 3.53. The superconducting gap decreases with temperature and vanishes at TC, in a manner similar to the BCS behavior but dramatically different from that of the nodal pseudogap behavior in cuprate superconductors.
