A transparent superconductor: mechanism and possible applications

2015 Fiscal Year Final Research Report

• Project/Area Number: 26610092
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Condensed matter physics II
• Research Institution: Tohoku University
• Principal Investigator: Hitosugi Taro 東北大学, 原子分子材料科学高等研究機構, 准教授 (90372416)
• Project Period (FY): 2014-04-01 – 2016-03-31
• Keywords: 透明導電体 / 透明超伝導 / 薄膜 / 酸化物

Outline of Final Research Achievements

A framework is presented for the transparent conducting mechanism of transparent superconductor LiTi2O4. In the Bardeen-Cooper-Schrieffer (BCS) framework, achieving high superconducting transition temperature requires a large carrier density at the Fermi energy. This requirement prohibits the emergence of transparent superconductivity at high temperature, since the large carrier density leads to the optical absorption in the visible region. However, we here demonstrate transparent superconducting properties with a transition temperature exceeding 13 K in spinel LiTi2O4(111) epitaxial thin films. Although the LiTi2O4 have a very large carrier density exceeding 10 22 cm-3, the film shows high transmittance in the visible region. Photoemission and optical studies indicate a band gap of ~3.3 eV with free electrons populating up to 0.5 eV from the bottom of the conduction band. Electron transport measurements and optical analyses suggest the key role of electron effective mass.

Free Research Field

固体化学