David Robert Nelson

David R. Nelson (born May 9, 1951, Stuttgart) is an American physicist, and Arthur K. Solomon Professor of Biophysics, at Harvard University.
Education and research.
David R. Nelson is currently the Arthur K. Solomon Professor of Biophysics and Professor of Physics and Applied Physics at Harvard University. He graduated from Cornell University "Summa cum laude" with a double major in physics and mathematics in 1972, and received an M.S. in Theoretical Physics in 1974, and a Ph.D. in Theoretical Physics in January, 1975. He was in the fourth and final class of Cornell's short-lived "Six-year Ph.D. program". He then became a Junior Fellow in the Harvard Society of Fellows.
Since 1978 he has been a professor at Harvard University. His research is in the fields of both hard and soft theoretical condensed matter physics, and of physical biology. His condensed matter research has focused on collective effects in the physics and chemistry of condensed matter and on spatial population genetics. He has been interested, in particular, in the interplay between fluctuations, geometry and statistical dynamics in condensed matter systems such as magnets, superfluids, liquid crystals, superconductors, polymers, turbulent fluids and metallic glasses. Nelson also has a strong interest in biological problems such as single molecule biophysics, population dynamics in inhomogeneous media, the buckling of viral shells and the effects of selective advantages, mutations, antagonism and cooperation on the spatial population genetics of microorganisms such as bacteria and yeast on both solid and liquid substrates.
With his colleague, Bertrand Halperin, he is responsible for a theory of two-dimensional melting that predicted a fourth "hexatic" phase of matter, interposed between the usual solid and liquid phases. A variety of predictions associated with this two-state freezing process have now been confirmed in experiments on two-dimensional colloidal assemblies, thin films and bulk smectic liquid crystals. Nelson's research also includes a theory of the structure and statistical mechanics of metallic glasses and investigations of "tethered surfaces,” which are two-dimensional generalizations of linear polymer chains. Flexural phonons lead a remarkable low temperature flat phase in these fishnet-like structures, with predictions of strongly scale-dependent elastic constants such as the two-dimensional Young’s modulus and the bending rigidity of atomically or molecularly thin materials such as a free-standing sheets of graphene and MoS2.
Nelson has also studied flux line entanglement in the high temperature superconductors. At high magnetic fields, thermal fluctuations cause regular arrays of flux lines to melt into a tangled spaghetti state. The physics of this melted flux liquid resembles that of a directed polymer melt, and has important implications for both electrical transport and vortex pinning for many of the proposed applications of these new materials in strong magnetic fields. 
David Nelson's recent investigations have focused on problems that bridge the gap between the physical and biological sciences, including dislocation dynamics in bacterial cell walls, range expansions and genetic demixing in microorganisms and localization in asymmetric sparse neural networks. Additional recent interests include the non-Hermitian transfer matrices that describe thermally excited vortices with columnar pins in Type II superconductors, the effect of perforations, cuts and other defects on atomically thin cantilevers at finite temperatures and topological defects on curved surfaces.