2nd Cross-Divisional Materials Research Program Unit Leaders' Special Seminar


Dr. Fumitaka Kagawa (Unit Leader, Dynamic Emergent Phenomena Research Unit, RIKEN CEMS)


13:30 - 14:30, August 2, 2017 (Wednesday)


Okochi-Hall, RIKEN


Condensed-matter research beyond thermo-equilibrium phase diagrams


Electrons in condensed matter have internal degrees of freedom, such as charge, spin and orbital, leading to various forms of ordered states through phase transitions. However, in individual materials, a charge/spin/orbital ordered state of the lowest temperature is normally uniquely determined in terms of the lowest-energy state, i.e., the ground state. In this presentation, I summarize recent studies showing that under rapid cooling, this principle does not necessarily hold, and thus, the cooling rate is a control parameter of the lowest-temperature state beyond the framework of the thermo-equilibrium phase diagram. An unconventionally high cooling rate, such as 102‒103 K/s, allows some systems to kinetically avoid a first-order phase transition, resulting in a quenched charge/spin state that differs from the ground state. I also show that quenched states can be exploited as a non-volatile state variable when designing phase-change memory functions. Control of macroscopic physical properties by means of domain manipulations is also discussed.