Texture (cosmology)

Abstract: We have observed an unconventional, likely topological, Hall effect over a wide temperature region in the magnetization process of a chiral-lattice helimagnet MnGe. The magnitude of the topological Hall resistivity is nearly temperature-independent below 70 K, which reflects the real-space fictitious magnetic field proportional to a geometric quantity (scalar spin chirality) of the underlying spin texture. From the neutron diffraction study, it is anticipated that a relatively short-period (3--6 nm) noncoplanar spin structure is stabilized from the proper screw state in a magnetic field to produce the largest topological Hall response among the B20-type (FeSi-type) chiral magnets.

Abstract: We study Weyl nodes in materials with broken inversion symmetry. We find based on first-principles calculations that trigonal Te and Se have multiple Weyl nodes near the Fermi level. The conduction bands have a spin splitting similar to the Rashba splitting around the $H$ points, but unlike the Rashba splitting the spin directions are radial, forming a hedgehog spin texture around the $H$ points, with a nonzero Pontryagin index for each spin-split conduction band. The Weyl semimetal phase, which has never been observed in real materials without inversion symmetry, is realized under pressure. The evolution of the spin texture by varying the pressure can be explained by the evolution of the Weyl nodes in $\mathbit{k}$ space.

Abstract: Topological Kondo insulators have been proposed as a new class of topological insulators in which non-trivial surface states reside in the bulk Kondo band gap at low temperature due to strong spin-orbit coupling. In contrast to other three-dimensional topological insulators, a topological Kondo insulator is truly bulk insulating. Furthermore, strong electron correlations are present in the system, which may interact with the novel topological phase. By applying spin- and angle-resolved photoemission spectroscopy, here we show that the surface states of SmB6 are spin polarized. The spin is locked to the crystal momentum, fulfilling time reversal and crystal symmetries. Our results provide strong evidence that SmB6 can host topological surface states in a bulk insulating gap stemming from the Kondo effect, which can serve as an ideal platform for investigating of the interplay between novel topological quantum states with emergent effects and competing orders induced by strongly correlated electrons.