CAM Exploratory Workshop Proposal
Branko Stojkovic
Los Alamos National Laboratory
CNLS, MS K765
Los Alamos, NM 87545
(505) 667-9958
(505) 665-2659
Collective Excitations as a Source of Nonlinearity in Soft Matter
CAM materials are characterized by the collective behavior of their ingredient particles, resulting in pattern formation on mesoscopic or even macroscopic scales. In both hard and soft condensed matter, the collective excitations are often due to the proximity of a system to a critical point, and hence symmetry breaking. The nonlinearity in this case stems not only from the competition of two phases, as is often the case in critical phenomena, but also from the induced interaction of single particles with collective excitations. For example, in the underdoped superconducting cuprates, the competition of these various interactions can lead to crossover behavior and to dynamic scaling, or, under some circumstances, to phase separation with a stable pattern forming, depending on the relative strengths of the interactions.
A good example in soft matter are lipid thin films: the competition of short-range attractions of the Lennard-Jones type and a dipolar repulsion in these films may lead to a spinodal decomposition. When mixed with other particles, such as cholesterol, the competition is even more pronounced and can lead to the formation of a droplet pattern and even to a geometric pattern of different phases.
A third example of collective behavior is found in biological matter. Thus in some proteins the function (e.g., rebinding of a small ligand, such as CO) is characterized by a collective motion of the whole protein. Here large binding (electronic) energies are quickly dissipated into collective modes (typically vibrational). Finally, DNA aggregation in solutions with mono and divalent counterions results from the competition of electrostatic forces and fluctuations in the density of counterions.
I would therefore like to propose that ICAM hold an exploratory workshop which brings together theorists and experimentalists working on these aspects of strongly correlated hard matter, soft matter, and biological matter to discuss both the similarities and differences in these and related systems, and to consider the possibility that this topic might emerge as one of ICAM's initial major research themes.