# Condensed Matter Theory

The Condensed Matter Theory group enjoys a great diversity of research programs that span forefront areas of hard/soft condensed matter physics as well as emerging areas at the intersection of physics and other disciplines. The group hosts several postdocs and visiting scientists and benefits from access to several on-campus state-of-the-art computational facilities. Highlights of current research activities of selected group members include:

### Electronic Structure and Spectroscopy of Novel Materials

Professor Arun Bansil is the past director of the Advanced Scientific Computation Center and of the ELMO Laboratory for science teaching. His research focuses on questions concerning the electronic structure and spectroscopy of high-temperature superconductors and other novel materials, including nano-particle systems. His group is developing and implementing theoretical methodologies for carrying out first-principles calculations of spectral intensities relevant for angle-resolved photoemission, resonant inelastic x-ray scattering, scanning tunneling microscopy, positron-annihilation angular correlation, and other highly resolved spectroscopies, including effects of strong electron correlations. These investigations are aimed at elucidating the nature of electronic states at and near the Fermi energy, the mechanism of superconductivity in high temperature superconductors, and a variety of other interesting questions, and involve extensive collaborations inside and outside the US.

### Nonlinear Physics at the Interface with Materials and Biology

Professor Karma’s research interest lies in theoretical understanding of the emergence of nonequilibrium patterns in nonlinear systems with applications to diverse problems in materials science and biology that are both of fundamental and practical relevance. This research makes extensive uses of mathematical models and computational approaches rooted in nonequilibrium statistical physics and nonlinear dynamics. In the materials arena, a main focus in his group has been the application of the phase-field method to microstructural evolution and crack propagation. The power of this method rests on the spatiotemporal coarse-graining of atomistic details that renders continuum scale simulations of interface dynamics feasible. Much of the excitement in this line research has been generated by recent successes to combine atomistic and phase-field methods to make materials specific predictions on experimentally relevant length and time scales, which is becoming increasingly feasible due to the rapid advances in computer power.

### Nanotribology in Crystalline and Polymeric Materials

Professor Jeff Sokoloff’s research focuses on elucidating complex atomic-scale mechanisms of wearless friction between solid surfaces using a variety of analytical and computational methods. Topics under current investigation include studies of a proposed mechanism for the reduction of friction by a lubricant, understanding why thin films are able to slide under the exceedingly weak inertial forces exerted on the films during quartz crystal oscillations in microbalance experiments designed for studying friction, and the fundamental study of lubrication mechanism due to polymer brush coatings.

### Theoretical/Computational Neuroscience

Analysis of neural circuits in the cerebral cortex is the primary research focus of Prof. Armen Stepanyants’ group. This group is utilizing computational and theoretical methods of statistical physics in the attempt to uncover the basic principles governing the circuit organization and function. To date, many fundamental questions about the brain remain unanswered: How do neurons find appropriate synaptic targets in the course of development and form functional circuits? How do these circuits change during learning and memory formation? What is the connectivity diagram of the brain? Due to the unparalleled complexity of the brain, answering these questions requires new theories and computational methods and will undoubtedly lead to new discoveries.

### Strongly Correlated Quantum Matter

Prof. Adrian Feiguin’s field of expertise is computational condensed matter, focusing on quantum mechanical problems with strong correlations. He conducts research on several topics ranging from quantum transport, to exotic phases of matter in cold atom systems. In modern condensed matter theory, the study of strongly correlated systems occupies the foremost area of research. This is motivated by the rich and exotic physics that emerges when the interactions in a quantum system are strong. When interactions behave non-pertubatively, they give rise some complex and intriguing phenomena, such as the Kondo effect, spin-charge separation, charge fractionalization, and fractional quantum statistics.

### Disordered Materials and Soft-Condensed Matter Theory

Prof. Bi’s group is interested in understanding collective and emergent behavior in out-of-equilibrium and disordered systems using methods in theoretical and computational physics. A recent focus is on bio-inspired amorphous metamaterials with special photonic and acoustic properties which can serve as the basis for new radiation sources, sensors, wave guides, solar arrays and optical computer chips. In the area of active matter, the group studies the non-linear rheology of dense suspensions driven by active energy input. In the area of granular materials, the group works to understand the interplay between friction, packing disorder and force chains

### Stochastic Modeling

Professor Alex Vespignani is working in the area of discrete stochastic epidemic computational modeling and more about his research can be found on the Network Science page.

### Complex Network Systems

Professor Laszlo Barabasi studies and models complex networks for a wide variety of systems using mathematical methods derived from statistical physics. More about his work can be found on the Network Science page.

### Network Theory

Professor Dmitri Krioukov’s research mainly focuses on theoretical and mathematical aspects of network science. He develops and applies methods in non-Euclidean geometry and theoretical physics to the analysis of complex networks. For more information, see the Network Science page.

The Condensed Matter Theory group includes Professors Arun Bansil, Albert-László Barabási, Dapeng “Max” Bi, Adrian Feiguin, Jorge José (Emeritus), Alain Karma, Dmitri Krioukov, Jeffrey Sokoloff (Emeritus), Armen Stepanyants, Alessandro Vespignani, Paul Whitford, and Fa-Yueh We (Emeritus).