### Department Research Activities:

Condensed Matter Theory

Condensed matter physics is notable for its diversity and breadth. Even the more traditional sub-area of solid state physics covers a bewildering array of physical phenomena, spanning the fields of magnetism, superconductivity, metals, semiconductors, insulators and more. But condensed matter physics also encompasses the science of “complex systems”, such as robustness of interconnected biological, ecological, and technological networks, earthquake source dynamics, crack propagation, polymers, liquid crystals, colloids, and most recently biological materials. Condensed matter theory at UCSB spans a broad swath of these diverse topics. With the presence of the Kavli Institute for Theoretical Physics (KITP), condensed matter theory at UCSB has enjoyed a stellar world-wide reputation. A brief description of the faculty and their interests follows.

**Leon Balents** works on a variety of topics associated with ordering, criticality, and phase coherence in quantum and classical systems. On the quantum side, these include phases and phase transitions of correlated electrons (in high Tc superconductors, transition metal oxides, and low- dimensional structures), atoms (in optical lattices), or spins (in frustrated magnets). He is also pursuing instances and applications of Berry phase, topology, and symmetry of spin-orbit coupled metals and semiconductors. On the classical front, he is studying the emergence of slow relaxation and metastability in disordered glasses.

**Frank Brown**'s interests center around the theoretical study of biological membranes and single molecule spectroscopy. His work involves a combination of analytical and numerical calculations and coarse-grained simulations. His group is currently interested in the development of continuum level (elastic, hydrodynamic) theories and simulation algorithms for the study of biomembranes and lipid bilayers and the theoretical description of photon counting spectroscopy experiments. Recent work in the group has applied these models to the study of protein diffusion on the surface of human red blood cells, the fluctuation dynamics of inter-membrane junctions and the dynamics of single enzymes in solution.

**Jean Carlson** studies novel nonlinear phenomena in systems far from equilibrium, including the rupture of earthquake faults, forest fires, evolution and extinction, and interconnected networks such as the internet. She has worked to develop new paradigms for thinking about such complex phenomena, including notions of “Highly Optimized Tolerance” ( HOT) and “complexity and robustness”, as well as new approaches such as multi-scale modeling and control theory.

**Wim van Dam**'s research focuses on the theory of quantum computation and all things related: quantum information, quantum communication, nonlocality, number theory, algebraic geometry and more. He holds a joint appointment with the department of Computer Science.

**Matthew Fisher** is interested in “novel” electronic materials that deviate from the standard paradigm of solid state physics due to strong Coulomb correlations, particularly d-shell transition metal oxides, f-shell rare earth compounds and some organic molecular crystals. Of especial interest are exotic quantum phases and criticality that are not present in familiar materials such as simple metals (copper), insulators (diamond), or semiconductors (silicon). He is also interested in ultracold atoms in optical traps where analogous phenomena should be accessible.

**Jim Langer** focuses on the theory of nonequilibrium phenomena, both at the microscopic and macroscopic levels. At the molecular level the problems involve the behavior of thermodynamically unstable or metastable states of matter, such as nucleation of phase separation in multi-component liquids and alloys, and thermally activated relaxation and aging in noncrystalline solids. At the macroscopic level, he has worked on problems of pattern formation, e.g., dendritic (snowflake- like) solidification. At present he is especially interested in theories of deformation and failure in noncrystalline solids, where both levels of analysis are required.

**Andreas Ludwig** is interested in problems which involve strong interactions or disorder, which cannot be understood within standard perturbative approaches. Examples are ubiquitous involving the Quantum Hall effect, quantum dots, Kondo effects, localization transitions, and many others. He employs novel analytic methods, including exact methods such as conformal field theory (developed in String Theory) and integrability.

**Chetan Nayak**'s work focuses on topological quantum computation and on non-Fermi liquid behavior in correlated electron systems.

**Phil Pincus**: "Our group is active in theoretical soft condensed matter physics. Most of our research is motivated by issues from biomolecular/cellular biophysics. While we bring to bear any relevant tools on the problem at hand, our emphasis is more on analytic rather than heavily computational methods. We have joint group meeting and projects with the group of Professor Frank Brown from the Department of Chemistry & Biochemistry. Current areas include electrostatic effects in biopolymers and biomembranes, cytoskeleton dynamics, correlated hydrogen bonding networks, polyelectrolyte brushes, conjugated polymers in aqueous solutions."

**Doug Scalapino** is primarily interested in high temperature superconductivity, and was the first proponent of the “d-wave pairing” scenario, since confirmed in these unusual materials. Doug has been a pioneer in developing and employing novel numerical techniques to attack models of strongly interacting electrons.

**Joan Shea**'s group focuses on developing and applying the techniques of statistical and computational physics to the study of biological problems. Current work involves the investigation of cellular processes including in-vivo protein folding and protein aggregation.

**Boris Shraiman**'s research interests focus on statistical mechanics of non-equilibrium systems, quantitative systems biology and bioinformatics.

**Cenke Xu **studies the unconventional states of matter and critical points between states of matter that are beyond the standard Landau’s paradigm. These phenomena usually emerge in condensed matter systems with interplay between strong interaction, quantum fluctuation, and nontrivial topological effects. He is also interested in the quantum entanglement of quantum many-body systems.