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# Theoretical Condensed Matter Physics

* *

## Kathryn Levin

Ph.D., Harvard, 1970.

Prof., Dept. Physics, James Franck Inst., and the College.

*Theoretical physics, solid state physics.*

Our work is based on many body quantum field theory and is closely tied to experiments. Our more recent research has been in the two theoretical fields of high temperature cuprate superconductors and ultracold atomic gas superfluids. We were among the first to investigate the more extended version of BCS (Bardeen Cooper Schrieffer) theory to the so called ‘‘crossover" between BCS and Bose Einstein condensation (BEC). Our original motivation was to understand anomalies in high temperature superconductors where, because of the small size of the Cooper pairs, one would expect that these materials are in the ‘‘crossover" region, intermediate between very loosely and very tightly bound pairs. [Pairing of fermions through an attractive interaction is an essential ingredient of superconductivity.] In the cuprates much more could be going on as well, but minimally one has to include these effects. And they surely give rise to so-called ‘‘pseudogap" effects, that is, an anomalous normal state above the transition temperature. Understanding the origin of this pseudogap still remains a central focus of the cuprate field.

Fortunately, in 2003 it was shown that there is a very nice laboratory for studying BCS- BEC crossover, and verifying some of our ideas about high temperature superconductors. This is in the ultracold Fermi gases which have attracted enormous attention to the concept of BCS-BEC crossover. We were in a rather unique position having a theory of the cuprates (there are literally hundreds in the literature) which has a clear realization in a laboratory. We have continued to work in this cold atom field making predictions and arriving at an a posteriori understanding of a vast treasure trove of experiments. Most recently (in 2014) we anticipated quite precisely the experimental story involving a long sequence of equilibrating steps associated with these superfluids when they are driven violently from equilibrium via ‘‘phase imprinting".

With the recent emphasis on topological order, we have begun to contribute to this field, by looking at spin-orbit effects in Fermi gas superfluids. Our focus is on calculating whether the transition temperatures are in a reasonable, physically accessible range, and also how one can probe these systems through precisely calculated correlation functions.

**Selected Publications:**

- Signatures of Pairing and spin-orbit coupling in correlation functions of Fermi gases, Chien-Te Wu, Brandon M. Anderson, Rufus Boyack and K. Levin [ArXiv 1503.05454]
- Phase Imprinting in Equilibrating Fermi Gases: The Transience of Vortex Rings and Other Defects, Peter Scherpelz, Karmela Padavic, Adam Rancon, Andreas Glatz, Igor Aranson and K Levin Phys. Rev. Lett. 113, 125301 (2014).
- Unified Treatment of Fermi pockets and arcs scenarios for the cuprates: Sum rule con- sistent response functions of the pseudogap Peter Scherpelz, Adam Rancon, Yan He and K. Levin PRB 90, 060506(R) (2014)
- Theory of Fluctuating Charge Ordering in the Pseudogap Phase of the Cuprates Via A Preformed Pair Approach, Yan He, Peter Scherpelz and K. Levin Phys. Rev. B 88, 064516 (2013)
- "Theory of Diamagnetism in the Pseudogap Phase: Implications from the Self energyof Angle Resolved Photoemission" Temperature Superconductors" Dan Wulin and K. Levin Phys. Rev. 86, 184513 (2012)

- Perfect fluids and Bad Metals: Insights from Ultracold Fermi gases. Hao Guo, D. Wulin, Chih-Chun Chien and K. Levin New Journal of Physics 13, 075011 (2011).
- Microscopic Approach to Viscosities in Superfluid Fermi Gases: From BCS to BEC. H. Guo, D. Wulin, Chih-Chun Chien, K. Levin Phys. Rev. Lett. 107, 020403 (2011).
- Establishing the Presence of Coherence in Atomic Fermi Superfluids: Spin Flip and Spin-Preserving Bragg Scattering at Finite Temperatures, Hao Guo, Chih-Chun Chien and K. Levin Phys. Rev. Lett 105, 120401 (2010).
- "BCS-BEC Crossover: From High Temperature Superconductors to Ultracold Super- fluids." Qijin Chen, Jelena Stajic, Shina Tan and K. Levin Physics Reports 412, 1 (2005).
- Heat Capacity of a strongly-Interacting Fermi Gas." J. Kinast, A. Turlapov, J.E. Thomas, Qijin Chen, Jelena Stajic, Science 307, 1296 (2005).

### Related Links:

- Papers from x-arXiv/cond-mat
- Honors
- Contact information

*Updated 2/2011*

## Michael Levin

PH.D., Massachusetts Institute of Technology, 2006.

Associate Prof., Dept. Physics, James Franck Inst., and the College*Theoretical physics, condensed matter physics*

Recently, my research has focused on two areas of quantum condensed matter physics. The first area is the study of "topological phases" of matter, such as quantum Hall liquids and topological insulators. These phases have a rich internal structure, but unlike conventional phases like magnets or superconductors, this structure has nothing to do with symmetry breaking or order parameters. Instead, the defining features of these phases have a topological character. As a result, entirely new concepts and tools need to be constructed to understand these systems. Much of my research is devoted to developing these new methods and approaches.

My second area of focus is at the intersection of quantum information theory and condensed matter physics. Here the fundamental problems are (1) to determine which quantum many-body systems can be efficiently simulated on a classical computer and (2) to develop methods to accomplish this task. In addition to its potential practical implications, this problem is closely related to many basic conceptual questions such as the nature of entanglement in many-body ground states and the classification of gapped quantum phases of matter.

**Selected publications:**

- M. Levin. Protected edge modes without symmetry. Phys. Rev. X 3, 021009 (2013).
- M. Levin and Z.-C. Gu. Braiding statistics approach to symmetry-protected topological phases. Phys. Rev. B 86, 115109 (2012).
- M. Levin and A. Stern. Fractional topological insulators. Phys. Rev. Lett. 103, 196803 (2009).
- M. Levin and C. P. Nave. Tensor renormalization group approach to 2D classical lattice models. Phys. Rev. Lett. 99, 120601 (2007).
- M. Levin and X.-G. Wen. Detecting topological order in a ground state wave function. Phys. Rev. Lett. 96, 110405 (2006).

### Related Links:

- Honors
- Contact Information

*Updated 10/2013*

## Peter B. Littlewood

Ph.D., Cambridge, 1980.

Prof., Dept. Physics, James Franck Inst., and the College; Associate Director - Physical Sciences & Engineering, Argonne Natl. Lab.

*Theoretical physics, condensed matter physics.*

Professor Littlewood's research has focused on the dynamics of collective transport; phenomenology and microscopic theory of high-temperature superconductors, transition metal oxides and other correlated electronic systems; and optical properties of highly excited semiconductors. He has applied his methods to engineering, including holographic storage, optical fibers and devices.

### Selected Publications (TBD):

- Band Structure of SnTe studies by Photoemission Spectroscopy, P.B. Littlewood, B. Mihaila, R.K. Schulze, D.J. Safarik, J.E. Gubernatis, A. Bostwick, E. Rotenberg, C.P. Opeil, T. Durakiewicz, J.L. Smith, and J.C. Lashley,
*Physical Review Letters*,**105**, 086404 (2010). - Polariton Condensates, D. Snoke and P.B. Littlewood,
*Physics Today*,**63**, 42 (August 2010).

### Related Links:

- Papers from x-arXiv/cond-mat
- Honors
- Contact information

*Updated 8/2012*

## Gene F. Mazenko

Ph.D., Massachusetts Institute of Technology, 1971.

Prof., Dept. Physics, James Franck Inst., and the College.

*Theoretical physics, statistical physics.*

Various materials, for example magnets, superconductors, liquid crystals, diblock copolymers and conventional solids, when temperature quenched from a high to a low temperature grow over time into ordered structures. In quenching a material from a temperature where it is a liquid down to a temperature corresponding to a solid we go from a material which is a uniform fluid to a final state where we have a crystalline solid. In the kinetic process taking us from the fluid to the crystal one finds intermediate states where the order is broken up by defects. Examples are dislocations in solids and vortices in magnets. We are interested in the appearance, motion and annihilation of these defects.

In the case of magnets and superfluids, where the final ordered state is uniform, the theory has been been developed to the state where we have been able to answer questions like: What is the velocity distribution for these evolving defects.

We are currently interested in the fundamental question of the nature of defect structures in pattern forming systems. Our interest is in those structures which form naturally under experimental circumstances. Our guide is to try and understand recent experiments on microphase separating diblock copolymer systems. Such systems grow a layered or striped phase. These systems are fundamentally important as prototypical two dimensional ordering systems but also as building blocks on the nano scale. Previously we have developed numerical techniques for looking at the nature of kinetic models proposed to describe systems of this type.

We are also working on the theoretical description of the kinetics of the liquid-glass transition. We have developed a new field theoretical model, called the hindered diffusion model, which leads naturally, to characteristic times which are activated, grow as e^{A/T} as temperature T is lowered. Much remains to be worked out for this model.

### Selected Publications:

- G.F. Mazenko, Vortex Velocities in the O(n) Symmetric TDGL Model.
*Phys. Rev. Lett***78**, 401, 1997. - H. Qian and G. F. Mazenko, Vortex Dynamics in a Coarsening Two Dimensional XY Model,
*Phys. Rev. E***68**, 021109/4 (2003). - H. Qian and G. F. Mazenko, Defect Structures in the Growth Kinetics of the Swift-Hohenberg Model,
*Phys. Rev. E***67**, 036102/12 (2003).

### Related Links:

- Papers from x-arXiv/cond-mat
- Honors
- Contact information

*Updated 8/2006*

## Dam T. Son

Ph.D., Institute for Nuclear Research - Moscow, 1995.

University Prof., Dept. Physics, Enrico Fermi Institute, James Franck Inst., and the College.

*Theoretical physics*

I have a broad research program encompassing several areas of theoretical physics.

*String Theory*: applications of gauge-gravity duality in the physics of the quark-gluon plasma and other strongly interacting systems.

*Nuclear Physics*: properties of the hot and dense states of matter, e.g., the quark gluon plasma and dense quark matter (color superconductors).

*Condensed matter physics*: physics of the quantum Hall system, graphene; applications of quantum field theory.

*Atomic physics*: many-body physics of cold trapped atoms, BCS-BEC crossover, applications of quantum field theoretical techniques.

### Selected Publications:

- R. Baier, A.H. Mueller, D. Schiff, and D.T. Son, "Bottom-up" thermalization in heavy ion collisions,
*Phys. Lett. B***502**, 51 (2001). - P. Kovtun, D.T. Son, and A.O. Starinets, Viscosity in Strongly Interacting Quantum Field Theories from Black Hole Physics,
*Phys. Rev. Lett*.**94**, 111601 (2005). - Y. Nishida and D.T. Son, Epsilon Expansion for a Fermi Gas at Infinite Scattering Length,
*Phys. Rev. Lett*.**97**, 050403 (2006). - C. Hoyos and D.T. Son, Hall Viscosity and Electromagnetic Response,
*Phys. Rev. Lett*.**108**, 066805 (2012).

### Related Links:

- Papers from arXiv.org
- Honors
- Contact information

*Updated 10/2012*

## Paul B. Wiegmann

Ph.D., Landau Inst., Moscow, 1978.

Robert W. Reneker Distinguished Service Professor, Dept. Physics, James Franck Inst., Enrico Fermi Inst., and the College.

*Theoretical physics, condensed matter physics.*

*Condensed Matter Physics*: Electronic Physics in Low Dimensions, Quantum Magnetism, Correlated Electronic Systems, Quantum Hall Effects, Topological aspects of Condensed Matter Theories, Electronic systems far from equilibrium.

*Statistical Mechanics*: Non-equilibrium Statistical Mechanics, Critical phenomena governed by Conformal Symmetry, Conformal stochastic processes, Stochastic geometry, Random Matrix Theory.

*Mathematical Physics*: Integrable Models of Quantum Field Theory and Statistical Mechanics, Quantum Groups and Representation theory, Anomalies in Quantum Field Theory, Conformal Field Theory, Quantum gravity.

*Nonlinear Physics*: Driven non-equilibrium systems, Turbulence, Fractal aspects of Pattern Formation, Interface Dynamics, Incommensurate Systems, Integrable aspects of nonlinear physics, Quantum Non-linear Phenomena.

Papers I've published since 1993 are available in x-arXiv/cond-mat and x-arXiv/hep-th.

### Related Links:

- Papers from x-arXiv/cond-mat
- Contact information

*Updated 2/2011*

## Thomas A. Witten

Ph.D., San Diego, 1971.

Prof. Emeritus, Dept. Physics, James Franck Inst., and the College

*Theoretical condensed matter physics, weakly-connected matter.*

Thomas Witten's homepage

My research concerns collective mechanisms for creating spontaneous structure in forms of conventional condensed matter such as polymer liquids, evaporating liquid drops, layer-forming surfactant micelles and thin elastic sheets. All these materials when subjected to structureless external forces develop new forms of spontaneous structure at a fine length scale, such as the sharp folds of a crumpled sheet or the thin ring stain left when a drop of dirty fluid has evaporated. These new forms of force-induced structure often arise from fundamental mechanical properties such as the competition between bending and stretching energy in an elastic sheet or between evaporative flows and capillary forces in an evaporating drop. They may arise from fundamental statistical properties such as the randomness of a chain polymer molecule or the random, tenuous structure of a colloidal aggregate. In either case the fundamental origins of the resulting structures mean that they can be used and manipulated in a wide range of material realizations independent of the specific properties of the materials.

### Selected Publications:

- Robust fadeout profile of an evaporation stain T. A. Witten,
*EPL***86**64002 (2009) - Chiral sedimentation of extended objects in viscous media Nathan W. Krapf, Thomas A. Witten, and Nathan C. Keim,
*Physical Review E***79**056307 (2009) - Stress focusing in elastic sheets T. A. Witten,
*Reviews of Modern of Physics*,**79** *Structured fluids: polymers, colloids, surfactants*(Oxford University Press: 2003)- Geometric origin of excess low-frequency vibrational modes in amorphous solids Matthieu Wyart, Sidney R. Nagel, T.A. Witten
*Europhysics Letters***71**1-7(2005)

### Related Links:

- Papers from x-arXiv/cond-mat
- Honors
- Contact information

*Updated 2/2011*

## Wendy Zhang

Ph.D., Harvard, 2001.

Associate Professor, Dept. of Physics, James

Franck Institute, and the College.

*Theoretical physics, soft condensed matter.*

I am interested in the formation of singularities, e.g. divergences in physical quantities such as pressure, on a fluid surface due to flow and surface tension effects. Two examples are the breakup of a liquid drop and viscous entrainment. In studying how nonlinear interactions give rise to singularities, we hope to understand the kinds of simplification in dynamics that can result when a physical process involves disparate length- and time-scales. We also hope that surface tension effects can be used to create structures which span a few molecules in one dimension but are macroscopic in other dimensions. More generally, thin tendril-like structures which extend over large distances arise in many contexts and can often strongly influence the large-scale dynamics. Examples include thermal and compositional convection, Coulomb fission and the formation of tether structure on a fluid surface due to optical radiation pressure. We use analytical methods, often based on asymptotic analysis, and numerical simulations. Many of the work are inspired by, or happen in parallel with, experimental work.

### Selected Publications

*Balance of actively generated contractile and resistive forces controls cytokinesis dynamics*. W. W. Zhang & D. N. Robinson, PNAS 102, 2005.*Drop Splashing on a Dry Smooth Surface.*L. Xu, W. W. Zhang & S. R. Nagel, Phys. Rev. Lett. 94 2005.*Viscous Entrainment from a Nozzle: Singular Liquid Spouts.*W. W. Zhang, Phys. Rev. Lett. 93 2004.*Persistence of Memory in Drop Breakup: The Breakdown of Universality*. P. Doshi, I. Cohen, W. W. Zhang, P. Howell, M. Siegel, O. A. Basaran, & S. R. Nagel, Science,**302**2003.*Shake-Gels: Shear-induced gelation of laponite-PEO mixtures.*J. Zebrowski, V. Prasad, W. W. Zhang, L. M. Walker & D. A. Weitz, Colloid & Surface Sci. A**213**2003.

### Related Links:

*Updated 6/2008 *