Emergent structures and clustering in active matter with non-reciprocal interactions: Interplay of Activity and Turn-away Torque

Roy, Somnath (2025) Emergent structures and clustering in active matter with non-reciprocal interactions: Interplay of Activity and Turn-away Torque. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Somnath Roy (20MS063)) 20MS063_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (15MB)

Abstract

This thesis explores the emergence of complex structural organization in two-dimensional active matter systems composed of self-propelled Brownian particles with non-reciprocal, torque-mediated interactions. Inspired by the flagellar avoidance dynamics of Chlamydomonas reinhardtii, the study employs numerical simulations and analytical tools-including mean-square displacement analysis, radial distribution functions, and structure factorsto investigate how torque strength, interaction range, and self-propulsion velocity govern phase transitions. Key findings reveal that increasing torque suppresses particle mobility by up to four orders of magnitude, driving hyperuniform-like regimes with suppressed density fluctuations. Intermediate torque induces crossover behavior from giant number fluctuations to near-hyperuniform scaling, while higher torque and larger interaction ranges produce novel self-organized states: dynamic filamentous chains with local nematic order and cluster crystals exhibiting hexatic arrangements. Reducing self-propulsion enhances ordering but reveals non-monotonic transitions in density correlations. The results map a rich phase diagram, demonstrating how non-reciprocal interactions and activity synergize to create tunable non-equilibrium architectures, bridging disordered fluids and crystalline solids. These insights advance the design of programmable active materials and deepen understanding of non-equilibrium statistical mechanics with non reciprocal interctaions. 5

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