Isao H. Inoue

Salle C313 « Nobelium », Bat C, 3eme étage jeudi 21 mars à 14h00

SUPERCONDUCTIVITY ENHANCED
BY A FERROELECTRIC QUANTUM CRITICAL POINT

Yasuhide Tomioka, Naoki Shirakawa, Keisuke Shibuya, Isao H. Inoue
National Institute of Advanced Industrial Science and Technology (AIST) : Tsukuba 305-8565, Japan

SrTiO3 is a well-known insulator with a band gap of 3.3 eV and shows many interesting properties. Notably, due to the substantial dielectric constant ε 24,000 at low temperatures, the effective Bohr radius becomes extremely large ( 0.5 μm), driving the insulator to metal transition even at a very low carrier density of 2×1016 cm−3. Although ε is huge, SrTiO3 does not show ferroelectricity ; this is called a quantum paraelectric because the low- temperature phase is close to a quantum critical point (QCP). Studies on QCPs so far have revealed remarkable phenomena such as superconductivity, but only around magnetic QCPs. In this talk, I will focus on the non-magnetic counterpart : ferroelectric QCP of SrTiO3. We explore the relationship between the superconductivity and the ferroelectric QCP of SrTiO3. We have prepared high-quality Sr1−xLaxTi(16O1−z18Oz)3 single crystal and systematically investigated the La substitution of Sr as an alternative of introducing oxygen vacancies. The superconducting transition temperature Tc shows a dome-like behaviour against the carrier density n. Analysis of the data based on a theoretical model predicts an appearance of the ferroelectric QCP for Sr1−xLaxTiO3 around 3×1018 cm−3. The QCP raises the superconducting dome of Sr1−xLaxTiO3 upwards. Further enhancement of Tc( 0.6 K) is achieved by 18O exchange on the Sr1−xLaxTiO3 crystals. These findings provide a new knob for observing intriguing physics around the ferroelectric QCP. Details are given in the talk. (Full abstract with figures can be downloaded from <https://goo.gl/tGL67n> .)

Short Biography
Dr Isao H. Inoue received BSc, MSc, and DSc degrees in Physics from the University of Tokyo in 1990, 1992 and 1998, respectively. He became a researcher with tenure of the Electrotechnical Laboratory (ETL) in 1992 and a senior researcher in 1999. From 1999 to 2001, he was a visiting scholar at Cavendish Laboratory, University of Cambridge. In 2001, ETL was reorganised to AIST ; since then, he has been a senior researcher of the National Institute of Advanced Industrial Science and Technology (AIST). He has been investigating on a wide range of research field : from the strongly correlated oxides to the neuromorphic electronic devices.

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