Research in the Reichman Group(A) Structure, Dynamics, Rheology and Self-Assembly of Soft Materials
For several years a major thrust of research in the Reichman group has been the theoretical description of the behavior and assembly of "soft" materials (colloidal suspensions, gels, membranes, polymer networks, etc). Our efforts in this broad area have spanned a range from analytical work (e.g. our work on sheared colloidal suspensions1,2), to coarse grained modeling (e.g. our work on non-equilibrium self-assembly of networks of nanoparticles3), to atomistic molecular dynamics and Monte Carlo simulations (e.g. our work on the interplay between microphase separation and gelation in charged attractive colloidal systems4 and more recent work on conjugated polymer modeling5,6,7). In this area we often collaborate with experimental groups at Columbia and elsewhere.
Click an image:(B) Statistical Mechanics of Disordered and Glassy Systems
Understanding the transition from a liquid to a glass has been called "the deepest and most interesting unsolved problem in solid state theory." Our group investigates the behavior of supercooled liquids and glasses using both analytical and computational tools. The Reichman group has made major contributions to understanding the role of activated transport and the onset of glassy dynamics in supercooled liquids,8,9 the description of non-linear susceptibilities related to dynamical heterogeneity10,11,12 and the connection between structure and dynamics in supercooled liquids.13 Currently a major effort in the group is aimed at distinguishing purely kinetic scenarios of the glass transition from those driven by non-trivial changes in the entropy of available configurations.
Click an image:(C) Out-of-Equilibrium Dynamics and Transport in Quantum Systems
Our group studies a wide variety of problems that involve the quantum behavior of correlated electronic systems that are driven out of equilibrium via contact to reservoirs held at different chemical potentials or temperatures or via a sudden change of interaction parameters (a "quantum quench").15 Our group uses analytical tools (e.g. bosonization) and has developed new numerical tools (e.g. iterative path-integral based schemes and exact real-time quantum Monte Carlo techniques) to investigate these problems.16,17,18,19,20,21
Click an image:(D) Quantum Liquids and Glasses
We have developed a microscopic theory to understand the dynamics of quantum fluids such as liquid para-Hydrogen.22 Our theory is in good agreement with transport and scattering experiments in these systems. Motivated by recent experimental and computational work suggesting novel features that arise from an interplay between intrinsically quantum mechanical fluctuations and glass formation, we have used our approach to predict how quantum fluctuations modify classical scenarios of the glass transition.23,24 In a slightly different context we are investigating under what conditions interactions can lead to equilibration of an otherwise non-ergodic assembly of particles or spins. A prime example of this type of quantum glass phenomena is the putative "many-body" localization transition whereby a non-ergodic Anderson-localized system may equilibrate if particle interactions are strong enough. We are investigating this transition using a variety of analytical and numerical approaches.25,26
Click an image:(E) Energy Transport in the Condensed Phase and in Photovoltaic Materials
The Reichman group is carrying out theoretical research to devise novel approaches for the description of exciton transport in complex condensed phase systems. The goals of this work are both fundamental and practical, with the applied component of the work directed towards optimizing the conversion of solar radiation to electrical energy. We have developed reduced density matrix theories that successfully describe general microscopic aspects of energy transport in condensed media,27,28 biological systems,29 and the process of singlet fission in organic crystals, whereby singlet excitons may rapidly and efficiently transform to multiple lower energy triplet excitons.30,31,32,33,34 This process may provide a means of increasing the efficiency of solar cells.
Click an image:(F) Optical and Electronic Properties of Layered Materials
Effort in the Reichman group has recently been aimed at understanding the behavior of novel two dimensional materials such as graphene, transition metal dichalcogenides and their heterostructures. Using electronic structure techniques we have successfully described the electronic properties of chemically doped graphene,35,36,37,38 bilayers of molybdenum disulfide,39 as well as the structural and electronic behavior of grain boundaries in transition metal dichalcogenides.40 Recently we have developed a simple theory that combines electronic structure theory with simple analytic elements for the excitonic properties of transition metal dichalcogenides. This theory has been shown to provide a quantitative description of excition, trion, and biexciton binding energies,41 as well as the excited state optical properties of these novel materials.42
Click an image:(G) Biophysical Transport
Our group has maintained an interest in biological transport problems such as how proteins find active sites along DNA43 and RNA44 and how biological cargo diffuse inside the crowded cellular environment.45 Some of this work has been motivated and carried out with various experimental groups at Columbia, such as the Greene Lab (Columbia Medical School) and the Prives Lab (Columbia Biology).
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