A topological superconductor (TSC) is characterized by the topologically protected gapless surface state that is essentially an Andreev bound state consisting of Majorana fermions. While a TSC has not yet been discovered, the doped topological insulator ${\mathrm{Cu}}_x{\mathrm{Bi}}_2{\mathrm{Se}}_3$, which superconducts below $\sim 3\mathrm{K}$, has been predicted to possess a topological superconducting state. We report that the point-contact spectra on the cleaved surface of superconducting ${\mathrm{Cu}}_x{\mathrm{Bi}}_2{\mathrm{Se}}_3$ present a zero-bias conductance peak (ZBCP) which signifies unconventional superconductivity. Theoretical considerations of all possible superconducting states help us conclude that this ZBCP is due to Majorana fermions and gives evidence for a topological superconductivity in ${\mathrm{Cu}}_x{\mathrm{Bi}}_2{\mathrm{Se}}_3$. In addition, we found an unusual pseudogap that develops below $\sim 20\mathrm{K}$ and coexists with the topological superconducting state.

Magnetic skyrmion textures are realized mainly in non-centrosymmetric, e.g. chiral or polar, magnets. Extending the field to centrosymmetric bulk materials is a rewarding challenge, where the released helicity/vorticity degree of freedom and higher skyrmion density result in intriguing new properties and enhanced functionality. We report here on the experimental observation of a skyrmion lattice (SkL) phase with large topological Hall effect and an incommensurate helical pitch as small as 2.8 nm in metallic Gd₃Ru₄Al₁₂, which materializes a breathing kagomé lattice of Gadolinium moments. The magnetic structure of several ordered phases, including the SkL, is determined by resonant x-ray diffraction as well as small angle neutron scattering. The SkL and helical phases are also observed directly using Lorentz-transmission electron microscopy. Among several competing phases, the SkL is promoted over a low-temperature transverse conical state by thermal fluctuations in an intermediate range of magnetic fields.

The superconductivity recently found in the doped topological insulator CuxBi2Se3 offers a great opportunity to search for a topological superconductor. We have successfully prepared a single-crystal sample with a large shielding fraction and measured the specific-heat anomaly associated with the superconductivity. The temperature dependence of the specific heat suggests a fully~gapped, strong-coupling superconducting state, but the BCS theory is not in full agreement with the data, which hints at a possible unconventional pairing in CuxBi2Se3. Also, the evaluated effective mass of 2.6me (me is the free electron mass) points to a large mass enhancement in this material.

We present measurements of the magnetic susceptibility and of the thermal expansion of a ${\mathrm{LaCoO}}_3$ single crystal. Both quantities show a strongly anomalous temperature dependence. Our data are consistently described in terms of a spin-state transition of the ${\mathrm{Co}}^{3+}$ ions with increasing temperature from a low-spin ground state ${(t}_{2g}^6{e}_g^0)$ to an intermediate-spin state ${(t}_{2g}^5{e}_g^1)$ without (100–500 K) and with $(>\mathrm{}500\mathrm{}\hspace{0.5em}\mathrm{K})$ orbital degeneracy. We attribute the lack of orbital degeneracy up to 500 K to (probably local) Jahn-Teller distortions of the ${\mathrm{CoO}}_6$ octahedra. A strong reduction or disappearance of the Jahn-Teller distortions seems to arise from the insulator-to-metal transition around 500 K.

We have performed spin- and angle-resolved photoemission spectroscopy of ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ and present the first direct evidence for the existence of the out-of-plane spin component on the surface state of a topological insulator. We found that the magnitude of the out-of-plane spin polarization on a hexagonally deformed Fermi surface of ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ reaches maximally 25% of the in-plane counterpart, while such a sizable out-of-plane spin component does not exist in the more circular Fermi surface of $\mathrm{TlBi}{\mathrm{Se}}_2$, indicating that the hexagonal deformation of the Fermi surface is responsible for the deviation from the ideal helical spin texture. The observed out-of-plane polarization is much smaller than that expected from the existing theory, suggesting that an additional ingredient is necessary for correctly understanding the surface spin polarization in ${\mathrm{Bi}}_2{\mathrm{Te}}_3$.