Second sound in the crossover from the Bose-Einstein condensate to the Bardeen-Cooper-Schrieffer superfluid

Second sound is an entropy wave which propagates in the superfluid component of a quantum liquid. Because it is an entropy wave, it probes the thermodynamic properties of the quantum liquid. Here, we study second sound propagation for a large range of interaction strengths within the crossover between a Bose-Einstein condensate (BEC) and the Bardeen-Cooper-Schrieffer (BCS) superfluid, extending previous work at unitarity. In particular, we investigate the strongly-interacting regime where currently theoretical predictions only exist in terms of an interpolation in the crossover. Working with a quantum gas of ultracold fermionic 6Li atoms with tunable interactions, we show that the second sound speed varies only slightly in the crossover regime. By varying the excitation procedure, we gain deeper insight on sound propagation. We compare our measurement results with classical-field simulations, which help with the interpretation of our experiments.

Programming Self-Assembled Materials With DNA-Coated Colloids

Introducing the concept of programmability paves the way for designing complex and intelligent materials, where the materials’ structural information is pre-encoded in the components that build the system. With highly tunable interactions, DNA-coated particles are promising building elements to program materials at the colloidal scale, but several grand challenges have prevented them from assembling into the desired structures and phases. In recent years, the field has seen significant progress in tackling these challenges, which has led to the realization of numerous colloidal structures and dynamics previously inaccessible, including the desirable colloidal diamond structure, that are useful for photonic and various other applications. We review this exciting progress, focusing in detail on how DNA-coated colloids can be designed to have a sophisticatedly tailored surface, shape, patches, as well as controlled kinetics, which are key factors that allow one to program in principle a limitless number of structures. We also share our view on how the field may be directed in future.

Assembly of a Patchy Protein into Variable 2D Lattices via Tunable, Multiscale Interactions

Self-assembly of molecular building blocks into higher-order structures is exploited in living systems to create functional complexity and represents a powerful synthetic strategy for constructing new materials. As nanoscale building blocks, proteins offer unique advantages, including monodispersity and atomically tunable interactions. Yet, control of protein self-assembly has been limited compared to that of inorganic or polymeric nanoparticles, which lack such attributes. We report modular self-assembly of an engineered protein into four physicochemically distinct, precisely patterned 2D crystals via control of four classes of interactions acting locally, regionally and globally. We relate the resulting structures to the underlying free-energy landscape by combining in-situ atomic force microscopy observations of assembly with thermodynamic analyses of protein-protein and -surface interactions. Our results demonstrate rich phase behavior obtainable from a single, highly-patchy protein when interactions acting over multiple length scales are exploited and predict new bulk-scale properties for protein based materials that ensue from such control.<div> </div>

Assembly of a Patchy Protein into Variable 2D Lattices via Tunable, Multiscale Interactions

Self-assembly of molecular building blocks into higher-order structures is exploited in living systems to create functional complexity and represents a powerful synthetic strategy for constructing new materials. As nanoscale building blocks, proteins offer unique advantages, including monodispersity and atomically tunable interactions. Yet, control of protein self-assembly has been limited compared to that of inorganic or polymeric nanoparticles, which lack such attributes. We report modular self-assembly of an engineered protein into four physicochemically distinct, precisely patterned 2D crystals via control of four classes of interactions acting locally, regionally and globally. We relate the resulting structures to the underlying free-energy landscape by combining in-situ atomic force microscopy observations of assembly with thermodynamic analyses of protein-protein and -surface interactions. Our results demonstrate rich phase behavior obtainable from a single, highly-patchy protein when interactions acting over multiple length scales are exploited and predict new bulk-scale properties for protein based materials that ensue from such control.<div> </div>

Colloids in rotating electric and magnetic fields: designing tunable interactions with spatial field hodographs

Spatially-rotating electric and magnetic fields open a way to designing tunable interactions between colloidal particles and provide rich opportunities both for fundamental studies and engineering of soft materials.