Dynamic Emergent Phenomena Research Unit

Principal Investigator

PI Name Fumitaka Kagawa
Degree D. Eng.
Title Unit Leader
Brief Resume
2006D.Eng., University of Tokyo
2006Research fellowship for young scientists
2007Researcher, JST-ERATO Multiferroic project
2010Project Lecturer, Quantum-Phase Electronics Center, University of Tokyo
2012Lecturer, Department of Applied Physics, University of Tokyo
2013Unit Leader, Dynamic Emergent Phenomena Research Unit, Cross-Divisional Materials Research Program, RIKEN Center for Emergent Matter Science (-present)
2017Associate Professor, Department of Applied Physics, University of Tokyo (-present)

Outline

Our unit explores dynamic phenomena exhibited by strongly correlated electron systems in both bulk and device structures to construct a new scheme for scientific investigation. In particular, we study external-field-driven dynamic phenomena exhibited by sub-micron-scale structures, such as topological spin textures and domain walls, using spectroscopy of dielectric responses and resistance fluctuations from the millihertz to gigahertz region. We also pursue real-space observations and measurements of local physical properties using scanning probe microscopy as a complementary approach. We are aiming to control novel physical properties exhibited by topological structures in condensed matter systems on the basis of knowledge obtained from these methods.

Research Fields

Physics, Materials Sciences

Keywords

Strongly correlated electron system
Organic ferroelectrics
Scanning probe microscopy
Spectroscopy

Results

Kinetic approach to superconductivity hidden behind a competing order

In strongly correlated electron systems, the emergence of superconductivity is often inhibited by the formation of a thermodynamically more stable magnetic/charge order. Nevertheless, by changing thermodynamic parameters, such as the physical/chemical pressure and carrier density, the free-energy balance between the superconductivity and the competing order can be varied, thus enabling the superconductivity to develop as the thermodynamically most stable state. We demonstrate a new kinetic approach to avoiding the competing order and thereby inducing persistent superconductivity. In the transition-metal dichalcogenide IrTe2 as an example, by utilizing current-pulse-based rapid cooling up to ~107 K s‒1, we successfully kinetically avoid a first-order phase transition to a competing charge order and uncover metastable superconductivity hidden behind. The present method also enables non-volatile and reversible switching of the metastable superconductivity with electric pulse applications, a unique advantage of the kinetic approach. Thus, our findings provide a new approach to developing and controlling superconductivity.

Conceptual phase diagram of superconductivity with ultra-rapid cooling (left), the thin-plate sample used in the experiments (top right) and non-volatile switching between superconducting and non-superconducting states demonstrated by resistivity measurements (bottom right)

Members

Fumitaka Kagawa

Unit Leader fumitaka.kagawa[at]riken.jp

Takuro Sato

Postdoctoral Researcher

Keisuke Matsuura

Special Postdoctoral Researcher

Hiroshi Oike

Visiting Scientist

Articles

お問い合わせ

2-1 Hirosawa, Wako, Saitama 351-0198 Japan

E-mail:
fumitaka.kagawa[at]riken.jp

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