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名古屋大学理学部物理学科R研の川崎猛史と申します。
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日時
2019年7月16日(火) 16:00～18:00
タイトル
Active glass and polycrystal: ergodicity breaking dramatically affects
response to self-propulsion
講演者
Mathieu Leocmach氏 (Université Claude Bernard Lyon 1 - CNRS, Université
de Lyon)
場所
東山キャンパス理学館 5F 506号室
アブストラクト
We study experimentally a sediment of self-propelled Brownian particles
with densities ranging from dilute to ergodic supercooled to nonergodic
glass, to nonergodic polycrystal. We observe a dramatic slowdown of
relaxation of nonergodic states when particles become weakly
self-propelled. By contrast, ergodic supercooled states always relax
faster with self-propulsion. Our system is a monolayer of micron-size
gold-platinum Janus particles, which become active upon adding a
solution of hydrogen peroxide due to self-phoretic propulsion
mechanisms. We characterise the activity level in our system with an
effective temperature defined from the density profile. Standard glassy
physics describes well the ergodic regime provided the replacement of
the ambient temperature by this effective temperature: higher
temperature implies faster relaxation. However beyond the glass
transition, the relaxation of the nonergodic system abruptly slows down
at low but nonzero activity. As we increase further activity, the
relaxation speeds up until it exceeds the passive situation. This
nonmonotonic behavior cannot be described by a simple increase in
temperature. The same nonmonotonic response is observed in polycrystal.
To explain this phenomenon, we correlated particle displacement
orientation and calculated the average length of correlated domains.
This length is inversely correlated with relaxation times, with small
lengths corresponding to slow relaxation. This suggests that relaxation
in sufficiently active nonergodic phase follows collective motion
mechanisms, while cooperative motion dominates at zero and low
activities. We propose that directed motion makes cage exploration less
efficient and thus slows down cooperative relaxation with respect to a
passive glass.
--
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Takeshi Kawasaki, PhD.
Assistant Professor
Department of Physics, Nagoya University,
Nagoya 464-8602, Japan
Tel/Fax: +81-52-789-2438
E-mail Address: kawasaki@r.phys.nagoya-u.ac.jp
URL: http://www.r.phys.nagoya-u.ac.jp/~kawasaki/index.html