第16回IPB セミナーシリーズ

[セミナー」第16回IPB セミナーを以下のように開催します。
日時：2020年11月4日（水）10:00-
場所：Zoom（要参加登録　here )
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講演者： 花井　亮　氏 (シカゴ大学)
タイトル：”Phase transitions in non-reciprocally interacting matter”
Abstract:
Usually, microscopic objects such as atoms and molecules obey the Newton’s third law, i.e., they interact in a reciprocal way. However, non-reciprocality is a common feature of active systems that arise in a broad context of science ranging from social sciences, biology to physics: A peregrine falcon chases a dove because of their non-reciprocal “interaction”; Neural networks are composed of inhibitory and excitatory neurons that couple non-reciprocally; Social networks are composed of nodes with non-reciprocal connectivity; Synthetic physical non-reciprocal interactions can be realized in complex plasma and optical nanoparticle systems.
Despite its ubiquitous presence in Nature, the collective properties of such non-reciprocally interacting many-body systems are poorly understood. In this talk, I will generalize the Ginzburg-Landau theory of equilibrium phase transitions to be applicable to non-reciprocal matter [1]. I show that non-reciprocity gives rise to unusual many-body phases and transitions controlled by spectral singularities called exceptional points. The emergent collective phenomena range from active time (quasi)crystals to exceptional point enforced pattern formation and hysteresis. I illustrate these phenomena by giving three paradigmatic examples of self-organization generalized to have non-reciprocal interactions: synchronization, flocking, and pattern formation.
If time allows, I will also talk about a quantum many-body system (exciton-polariton system) that exhibits analogous phase transitions [3] and critical phenomena (“critical exceptional point”), which is associated with a new universality class with anomalously giant phase fluctuations (that diverges at d≤4) and enhanced many-body correlations (that becomes relevant at d<8) [4]. [1] M. Fruchart*, R. Hanai*, P. B. Littlewood, and V. Vitelli, arXiv:2003.13176. [2] T. Kato, Perturbation theory for linear operators, 2nd ed. (Springer, 1984). [3] R. Hanai, A. Edelman, Y. Ohashi, and P. B. Littlewood, Phys. Rev. Lett. 122, 185301 (2019). [4] R. Hanai and P. B. Littlewood, Phys. Rev. Research 2, 033018 (2020). 講演は英語で行われます。 The talk will be given in English.