Visualization of spatial inhomogeneity in the superconducting gap using micro-ARPES.

Electronic inhomogeneity arises ubiquitously as a consequence of adjacent and/or competing multiple phases or orders in strongly correlated electron systems. Gap inhomogeneity in high- cuprate superconductors has been widely observed using scanning tunneling microscopy/spectroscopy. However, it has yet to be evaluated by angle-resolved photoemission spectroscopy (ARPES) due to the difficulty in achieving both high energy and spatial resolutions.

New three-dimensional flat band candidate materials PbAsO and PbSnO.

Energy dispersion of electrons is the most fundamental property of the solid state physics. In models of electrons on a lattice with strong geometric frustration, the band dispersion of electrons can disappear due to the quantum destructive interference of the wavefunction. This is called a flat band, and it is known to be the stage for the emergence of various fascinating physical properties.

Accelerated Lanthanide Intercalation into Graphite Catalyzed by Na.

Lanthanides () are notoriously difficult to intercalate into graphite. We investigated the possibility of using Na to catalyze the formation of -intercalated graphite and successfully synthesized C ( = Sm, Eu, and Yb) significantly rapidly in high yields. The synthesis process involves the formation of the reaction intermediate NaC, through the mixing of Na and C, which subsequently reacts with upon heating to form C.

Anisotropic atomic displacements, local orthorhombicity and anomalous local magnetic moment in BaKFeAs superconductor.

We have investigated the in-plane local structure of the BaKFeAs superconductor by polarized Fe K-edge extended X-ray absorption fine structure (EXAFS) measurements with temperature. The near neighbor bond distances and their stiffness, measured by polarized EXAFS in two orthogonal directions, are different suggesting in-plane anisotropy of the atomic displacements and local orthorhombicity in the title system. The X-ray absorption near edge structure (XANES) spectra reveal anisotropy of valence electronic structure that changes anomalously below ∼100 K.

Optically Probing Unconventional Superconductivity in Atomically Thin BiSrCaYCuO.

Atomically thin cuprates exhibiting a superconducting phase transition temperature similar to that of the bulk have recently been realized, although the device fabrication remains a challenge and limits the potential for many novel studies and applications. Here, we use an optical pump-probe approach to noninvasively study the unconventional superconductivity in atomically thin BiSrCaYCuO (Y-Bi2212). Apart from finding an optical response due to the superconducting phase transition that is similar to that of bulk Y-Bi2212, we observe that the sign and amplitude of the pump-probe signal in atomically thin flakes vary significantly in different dielectric environments depending on the nature of the optical excitation.