## Research in the Reichman Group

- (A) Structure, Dynamics, Rheology and Self-Assembly of Soft Materials
- (B) Statistical Mechanics of Disordered and Glassy Systems
- (C) Out-of-Equilibrium Dynamics and Transport in Quantum Systems
- (D) Quantum Liquids and Glasses
- (E) Charge and Energy Transport in Nanoscale Systems for Efficient Energy Conversion
- (F) Biophysical Transport

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 suspensions^{1,2}), to coarse grained modeling (e.g. our work on non-equilibrium self-assembly of networks of nanoparticles^{3}), to atomistic molecular dynamics and Monte Carlo simulations (e.g. our work on the interplay between microphase separation and gelation in charged attractive colloidal systems^{4}). In this area we often collaborate with experimental groups such as the Weitz Group (Harvard)^{5,6,7}, the Brus Group (Columbia)^{3} and the Whitesides Group (Harvard)^{8}.

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(B) Statistical Mechanics of Disordered and Glassy SystemsUnderstanding the transition from a liquid to a glass has been called "the deepest and most interesting unsolved problem in solid state theory^{9}." 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^{10,11}, the description of non-linear susceptibilities related to dynamical heterogeneity^{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^{14}.

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(C) Out-of-Equilibrium Dynamics and Transport in Quantum SystemsOur 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) to investigate these problems.

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(D) Quantum Liquids and GlassesWe have developed a microscopic theory to understand the dynamics of quantum fluids such as liquid para-Hydrogen^{16}. Our theory is in good agreement with transport and scattering experiments in these systems^{17,18}. Motivated by recent experimental and computational work suggesting novel features that arise from an interplay between intrinsically quantum mechanical fluctuations and glass formation^{19,20}, we are currently using our approach to predict how quantum fluctuations modify classical scenarios of the glass transition. 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^{21}. A prime example of this type of quantum glass phenomena is the putative many-body localization transition whereby (non-interacting) Anderson localization is speculated to transform into a finite temperature or finite coupling metal-insulator transition in the presence of particle interactions^{22,23}. We are investigating this putative transition via a variety of numerical approaches.

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(E) Charge and Energy Transport in Nanoscale Systems for Efficient Energy ConversionUnder the auspices of Columbia’s Energy Frontier Research Center (EFRC) we are carrying out theoretical research aimed at optimizing the conversion of solar radiation to electrical energy. Our areas of focus combine techniques we have developed in areas (A) and (C) above. In particular, we are using methods from quantum relaxation theory (e.g. non-equilibrium Green’s functions and reduced density matrices) married with methods from electronic structure theory to investigate charge multiplication in nanotubes and other nanostructures, as well as exciton fission in organic materials. We are also investigating how phase and microphase separation may be optimized for the formation of bulk heterojunction devices.

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(F) Biophysical TransportOur group has maintained an interest in biological transport problems such as how proteins find active sites along DNA^{24} and how biological cargo diffuse inside the crowded cellular environment^{25}. 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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References

- (1) , Molecular hydrodynamic theory of supercooled liquids and colloidal suspensions under shear. Physical Review E 66, 050501 (2002).
- (2) , Supercooled liquids under shear: Theory and simulation. Physical Review E 70, 011501 (2004).
- (3) , Drying-mediated self-assembly of nanoparticles. Nature 426, 271 (2003).
- (4) , Phase behavior and far-from-equilibrium gelation in charged attractive colloids. Physical Review E 75, 050401 (2007).
- (5) , Anomalous diffusion probes microstructure dynamics of entangled F-actin networks. Physical Review Letters 92, 178101 (2004).
- (6) , Glasslike arrest in spinodal decomposition as a route to colloidal gelation. Physical Review Letters 95, 238302 (2005).
- (7) , Soft colloids make strong glasses. Nature 462, 83-86 (2009).
- (8) , Magnetic self-assembly of three-dimensional surfaces from planar sheets. Proceedings of the National Academy of Sciences 102, 3924 (2005).
- (9) , Through the glass lightly. Science 267, 1609-1618 (1995).
- (10) , Trap models and slow dynamics in supercooled liquids. Physical Review Letters 90, 025503 (2003).
- (11) , Mean-field theory, mode-coupling theory, and the onset temperature in supercooled liquids. Physical Review E 69, 041202 (2004).
- (12) , Inhomogeneous mode-coupling theory and growing dynamic length in supercooled liquids. Physical Review Letters 97, 195701 (2006).
- (13) , Irreversible reorganization in a supercooled liquid originates from localized soft modes. Nature Physics 4, 711-715 (2008).
- (14) , Dynamical heterogeneity in lattice glass models. Journal of Chemical Physics 132, 044510 (2010).
- (15) , Nonequilibrium quantum dissipation in spin-fermion systems. Physical Review B 76, 195316 (2007).
- (16) , A fully self-consistent treatment of collective fluctuations in quantum liquids. Journal of Chemical Physics 120, 1458-1465 (2004).
- (17) , Self-consistent mode-coupling theory for self-diffusion in quantum liquids. Physical Review Letters 87, 265702 (2001).
- (18) , Collective and single-particle dynamics in liquid ortho-deuterium: A quantum mode-coupling approach. Europhysics Letters 60, 656-662 (2002).
- (19) , Evidence for a Superglass State in Solid He-4. Science 324, 632-636 (2009).
- (20) , Superglass phase of He-4. Physical Review Letters 96, 105301 (2006).
- (21) , Lecture notes about many-body localization. Princeton Summer School Lecture Notes [link] (2009).
- (22) , Metal-insulator transition in a weakly interacting many-electron system with localized single-particle states. Annals of Physics 321, 1126 (2006).
- (23) , Localization of interacting fermions at high temperature. Physical Review B 75, 155111 (2007).
- (24) , Dynamic basis for one-dimensional DNA scanning by the mismatch repair complex Msh2-Msh6. Molecular Cell 28, 359-370 (2007).
- (25) , The subdiffusive targeting problem. Journal of Physical Chemistry B 112, 4283-4289 (2008).