Electric field-induced superconducting transition of insulating FeSe thin film at 35 K

• Published in: Proceedings of the National Academy of Sciences - PNAS 2016-04, Vol.113 (15), p.3986-3990
• Main Authors: Hanzawa, Kota, Sato, Hikaru, Hiramatsu, Hidenori, Kamiya, Toshio, Hosono, Hideo
• Format: Article
• Language: English
• Subjects: Electric fields; Insulation; Physical Sciences; Superconductivity; Temperature; Thin films
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1520810113

It is thought that strong electron correlation in an insulating parent phase would enhance a critical temperature (T c) of superconductivity in a doped phase via enhancement of the binding energy of a Cooper pair as known in high-T c cuprates. To induce a superconductor transition in an insulating phase, injection of a high density of carriers is needed (e.g., by impurity doping). An electric double-layer transistor (EDLT) with an ionic liquid gate insulator enables such a field-induced transition to be investigated and is expected to result in a high T c because it is free from deterioration in structure and carrier transport that are in general caused by conventional carrier doping (e.g., chemical substitution). Here, for insulating epitaxial thin films (∼10 nm thick) of FeSe, we report a high T c of 35 K, which is 4× higher than that of bulk FeSe, using an EDLT under application of a gate bias of +5.5 V. Hall effect measurements under the gate bias suggest that highly accumulated electron carrier in the channel, whose area density is estimated to be 1.4 × 1015 cm–2 (the average volume density of 1.7 × 1021 cm–3), is the origin of the high-T c superconductivity. This result demonstrates that EDLTs are useful tools to explore the ultimate T c for insulating parent materials.