p-type transparent superconductivity in a layered oxide

Development of p-type transparent conducting materials has been a challenging issue. The known p-type transparent conductors unsatisfy both of high transparency and high conductivity nor exhibit superconductivity. Here, we report on epitaxial synthesis, excellent p-type transparent conductivity, and two-dimensional superconductivity of Li(1−x)NbO(2). The LiNbO(2) epitaxial films with NbO(2) sheets parallel to (111) plane of cubic MgAl(2)O(4) substrates were stabilized by heating amorphous films. The hole doping associated with Li(+) ion deintercalation triggered superconductivity below 4.2 kelvin. Optical measurements revealed that the averaged transmittance to the visible light of ~100-nanometer-thick Li(1−x)NbO(2) was ~77%, despite the large number of hole carriers exceeding 10(22) per cubic centimeter. These results indicate that Li(1−x)NbO(2) is a previously unknown p-type transparent superconductor, in which strongly correlated electrons at the largely isolated Nb 4d(z2) band play an important role for the high transparency.