Active Chiral Matter in Biology and Physics

Active Chiral Matter in Biology and Physics
Alexander Petroff, Clark University, Department of Physics
Alexander Petroff
Date and time: Thu, Dec 08, 2022 - 11:30am
Refreshments at 11:15am
Location: LGRT 1033
Category: Condensed Matter Seminar

The sediment-dwelling bacterium Thiovulum majus, which swims at a speed of 600 um/s, is one of the fastest known bacteria. When such a cell collides with a hard surface it either escapes rapidly into the bulk fluid or else becomes hydrodynamically bound to the wall. We first show that these dynamics preserve a memory of the cell's trajectory before the collision, which is gradually erased by contact with the surface. This erasure of information is consistent with a first-passage problem. Next, we investigate the two-dimensional motion of cells that are hydrodynamically bound to the surface. These cells diffuse laterally over the surface. When two cells diffuse within a critical distance of one another, they form a stable dimer of co-rotating cells. These dimers grow into two-dimensional active crystals composed of hundreds of cells. We develop a model of cell-cell interactions that gives insight into the large-scale motion and stability of these active chiral crystals. We then realize these dynamics in an artificial system composed of intrinsically spinning particles. This physical realization allows us to systematically vary the packing fraction of particles and examine associated phase transitions.