Hyperuniform Structures Formed by Shearing Colloidal Suspensions.

Area of Science:

• Soft matter physics
• Non-equilibrium statistical mechanics
• Complex fluids

Background:

• Dynamical phase transitions occur in periodically sheared suspensions between reversible absorbing states and chaotic active states.
• Repulsive nonhydrodynamic interactions are hypothesized to break time-reversal symmetry, driving this transition.
• Absorbing state models, like random organization, exhibit hyperuniformity at criticality, characterized by suppressed long-wavelength density fluctuations.

Purpose of the Study:

• To experimentally investigate the structural organization of particles in periodically sheared suspensions near the critical shear amplitude.
• To determine if hyperuniformity, a hallmark of absorbing state models, is present in these driven systems.
• To characterize the nature of order (short-range vs. long-range, anisotropic vs. isotropic) at the dynamical phase transition.

Main Methods:

• Experimental realization of periodically sheared suspensions.
• Varying oscillatory shear amplitudes to approach the critical strain amplitude (γc).
• Structural analysis using techniques to probe short-range and long-range order, including the structure factor S(q).

Main Results:

• Particles in sheared suspensions exhibit anisotropic short-range order.
• Isotropic, long-range hyperuniform order is observed as shear amplitudes approach the critical value (γc).
• The structure factor S(q) demonstrates behavior consistent with hyperuniformity (S(q→0)∼q^{α} with α>0) at criticality.

Conclusions:

• Periodically sheared suspensions experimentally realize hyperuniformity at a dynamical phase transition.
• The transition involves a shift from disordered or short-range ordered states to states with long-range isotropic hyperuniform order.
• This provides experimental evidence linking driven systems with absorbing phase transition characteristics and emergent hyperuniform states.