I am a theoretical physicist studying condensed matter. My main interest is in the properties of “strongly correlated” materials and devices, in which electron-electron interactions yield new states of matter. The zero-temperature phase transitions between correlated quantum states are an especially beautiful and universal part of this field. Another currently exciting area is understanding how correlated quantum states transport charge, spin, and heat: aside from fundamental interest, this can lead to new devices for spin-based electronics and new thermoelectric materials. We also use concepts from quantum information theory to analyze problems in condensed matter physics. Theoretical work on these problems benefits from an increasing quantity and quality of experimental data, and students in the group are encouraged to interact with experimental efforts at Berkeley and elsewhere.
Quantum phase transitions: One current research topic is the theory of disorder-driven quantum phase transitions, such as superconductor-insulator and Hall transitions: these show universal scaling laws but are not nearly as well understood as their classical analogues. There is a highly successful theory of classical phase transitions which also describes a few quantum phase transitions, but not those of the greatest experimental importance. There are several complex and poorly understood materials such as the cuprate superconductors and heavy-fermion compounds which seem experimentally to show quantum phase transitions. Although there is a shortage of nonperturbative methods in dimensions greater than one, some useful examples have appeared in the last few years.
Interaction effects in nanoscale devices: The effects of electron-electron interactions become especially dramatic when electrons are confined in quantum dots (zero-dimensional systems), nanotubes or quantum wires (one-dimensional), or quantum wells (two-dimensional). Experimentalists are now creating a wide variety of tiny devices and in many cases accessing regimes where a weakly interacting description misses essential physics. In many such problems, a few localized quantum variables, such as a single spin or the electrons on a superconducting grain, interact with a “sea” of surrounding electrons or phonons which can fundamentally modify the dynamics of the localized degrees of freedom. As an example, in the Kondo effect an unpaired spin forms a correlated state with the surrounding electrons, and experimentalists can now observe and control this behavior in single atoms, molecular transistors, and quantum dots.
Other topics in condensed matter theory: Although recently the above projects have taken up most of my time, there are many other areas in which similar analytical and computational techniques can be applied. Two of my physics “hobbies” are the physics of percolation and polymers, and applications of statistical physics to information theory and computing. Students are welcome to drop by and discuss specific problems in which they have an interest or condensed matter theory in general.
C. Xu and J. E. Moore, ``Strong-weak coupling self-duality in the two-dimensional quantum phase transition of p+ip superconducting arrays'', Phys. Rev. Lett.93, 047003 (2004).
G. Refael and J. E. Moore, ``Entanglement entropy of random quantum critical points in one dimension'', Phys. Rev. Lett.93, 260602 (2004).
C. P. Weber, N. Gedik, J. E. Moore, J. W. Orenstein, J. Stephens, and D. D. Awschalom, ``Observation of spin Coulomb drag in a two-dimensional electron gas'', Nature 437, 1330 (2005).
E. Fradkin and J. E. Moore, ``Entanglement entropy of 2D conformal quantum critical points: hearing the shape of a quantum drum'', Phys. Rev. Lett.97, 050404 (2006).
S. Mukerjee, C. Xu, and J. E. Moore, ``Topological defects and the superfluid transition of the s=1
spinor condensate in two dimensions'', Phys. Rev. Lett.97, 120406 (2006).
J. E. Moore and L. Balents, ``Topological invariants of time-reversal-invariant band structures'', Phys. Rev. B (Rapid Communcations)75, 121306 (2007).
Other papers are available at http://xxx.lanl.gov