Memory-less response and violation of the fluctuation-dissipation theorem in colloids suspended in an active bath

• Published in: Scientific reports Vol. 7; no. 1; pp. 17588 - 7
• Main Authors: Maggi, Claudio, Paoluzzi, Matteo, Angelani, Luca, Di Leonardo, Roberto
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 14-12-2017; Nature Publishing Group
• Subjects: 119/118; 14; 14/63; 639/766/530/2804; 639/766/747; Bacteria; Biomechanical Phenomena; Colloids; Copper; E coli; Equilibrium; Escherichia coli; Friction; Humanities and Social Sciences; Magnetic fields; Models, Theoretical; multidisciplinary; Noise; Reynolds number; Rheology; Science; Science (multidisciplinary); Stochastic Processes; Stochasticity; Suspensions; Time Factors; Viscosity
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-17900-2

We investigate experimentally and numerically the stochastic dynamics and the time-dependent response of colloids subject to a small external perturbation in a dense bath of motile
E
.
coli
bacteria. The external field is a magnetic field acting on a superparamagnetic microbead suspended in an active medium. The measured linear response reveals an instantaneous friction kernel despite the complexity of the bacterial bath. By comparing the mean squared displacement and the response function we detect a clear violation of the fluctuation dissipation theorem.