Spectroscopic Evidence for Multigap Superconductivity of Y at Megabar Pressures

The recent discovery of room-temperature superconductivity (RTSC) at pressures of several megabars has led to intensive efforts to probe the origin of superconducting (SC) electron pairs. Although the signatures of the SC phase transition have been well established, few reports of the SC properties of RTSCs have been published because of the diamond anvil cell (DAC) environments. Here, we report the first direct evidence of two SC gaps in Y metal via point-contact spectroscopy (PCS) in DAC environments, where a sharp peak at the zero-bias voltage in the differential conductance is overlaid with a broad peak owing to Andreev reflection. Analysis based on the Blonder-Tinkham-Klapwijk (BTK) model reveals the existence of two SC gaps: the larger gap is 3.63 meV and the smaller gap is 0.46 meV. The temperature dependence of the two SC gaps is well explained by the BCS theory, indicating that two-band superconductivity is realized in Y metal. The successful application of PCS to Y in DAC environments is expected to guide future research on the SC gap in megabar high-Tc superconductors.Comment: 17 pages, 4 figure

Triple-sinusoid hedgehog lattice in a centrosymmetric Kondo metal

Superposed symmetry-equivalent magnetic ordering wave vectors can lead to topologically non-trivial spin textures, such as magnetic skyrmions and hedgehogs, and give rise to novel quantum phenomena due to fictitious magnetic fields associated with a non-zero Berry curvature of these spin textures. To date, all known spin textures are constructed through the superposition of multiple spiral orders, where spins vary in directions with constant amplitude. Recent theoretical studies have suggested that multiple sinusoidal orders, where collinear spins vary in amplitude, can construct distinct topological spin textures regarding chirality properties. However, such textures have yet to be experimentally realised. In this work, we report the observation of a zero-field magnetic hedgehog lattice from a superposition of triple sinusoidal wave vectors in the magnetically frustrated Kondo lattice CePtAl4Ge2. Notably, we also observe the emergence of anomalous electrical and thermodynamic behaviours near the field-induced transition from the zero-field topological hedgehog lattice to a non-topological sinusoidal state. These observations highlight the role of Kondo coupling in stabilising the zero-field hedgehog state in the Kondo lattice and warrant an expedited search for other topological magnetic structures coupled with Kondo coupling

The characterization of (n−1)\mathbf{(n-1)}-spheres with n+4\mathbf{n+4} vertices having maximal Buchstaber number

16 pages, 4 tables, 1 figure, 1 algorithmWe provide a GPU-friendly algorithm for obtaining all weak pseudo-manifolds whose facets are all in an input set of facets satisfying given conditions. We use it here to completely list up toric colorable seed PL-spheres with a few vertices implying the complete characterization of PL-spheres of dimension $n-1$ with $n+4$ vertices having maximal Buchstaber numbers

The Korean Wave in Media. Seoul: Korea Press Foundation [in Korean] 해외 언론의 한류 보도 분석 연구

This is a multi-country analysis of the media coverage on the Korean wave phenomenon. It critically reviews the origin of the Korean wave in the late 1990s and analyses the ways in which this phenomenon has been reported in the mainstream media of China, the United States, Japan, UK and France. This book is an output of the research project funded by the Korea Press Foundation