Research Interests and Key Results

Materials - Synthesis of New Key Superconducting Materials

"At the extreme forefront of research in superconductivity is the empirical search for new materials." One of my research targets is the syntesis of new high-temperature superconductors by Molecular Beam Epitaxy (MBE), which, we have demonstrated as follows, is capable of opening up a novel synthetic route for new key materials.

Around 10 years ago, we discovered several brand-new superconductors such as Ba2CuO4-d, Sr2CuO4-d, and PbSr2CuO5+d, which cannot be obtained by conventional solid-state reaction. Later on, our group has also succeeded in synthesizing (La, Ce)2CuO4 (Tc~30K) and (Sr, La)CuO2 (Tc~43K), high-quality samples of which are difficult to obtain by bulk synthesis.

In 2004, we presented a series of new "non-doped" superconductors, which, we believe, are one of the key materials for understanding the high-Tc physics: they are nominally -undoped T'-(La, RE)2CuO4 (RE = Sm, Eu, Gd, Tb, Lu, Y). Here, the isovalent RE substitution is necessary to stabilize the T' structure.

Very recently, the pristine endmembers of T' materials, namely, RE2CuO4 (RE = Pr, Nd, Sm, Eu, Gd), which have been believed to be Mott-insulators, are found to be superconducting with even higher-Tc than their electron-doped analogues via MOD synthesis at TUAT. Preparation of these superconductors by MBE will provide a good opportunity for investigating the high-Tc physics, which eventually guides us towards higher-Tc superconductors.

Physics - in-situ ARPES of MBE films

Angle-resolved Potoemission Spectroscopy (ARPES) has been proven to be a powerful tool for investigating electronic structure of materials, especially for E-k dispersion near Fermi level. Combination of ARPES and MBE enables such investigations for (1) materials and/or single crystals only attainable by MBE, (2) non-cleavable materials, as well as significantly relaxes restrictions arising from the surface sensitivity. By taking advantage of the merits, we have successfully mapped the Fermi surface of the 30K-class electron-doped T'-(La, Ce)2CuO4.
ARPES with MBE films would provide a critical clue to understanding the apparent discrepancy between the present consensus of high-Tc physics and superconductivity observed in the non-doped cuprates. Such an attempt is under way.

Application - sorry under construction