Group members

Group photos and pages

Selected courses/seminars

PI contact information

Current interests

Theoretical condensed matter physics. The primary challenge of condensed matter is to understand how Maxwell's equations and quantum mechanics, the fairly simple "rules of the game," give rise to almost all of the complex phenomena we observe in nature. A succinct expression of this idea is More is different, the title of a 1972 Science article by Philip Anderson. Another thrust of condensed matter physics is to use what we have learned about collective states of electrons (or photons or atoms) to create devices, such as the transistor, laser, and SQUID, that have the potential to change lives.

Our primary interest is in properties of solids beyond the standard approximations of independent particles and perfect periodicity. For example, transport of heat, charge, and spin in materials would be dissipationless in the absence of defects and interparticle interactions. Understanding any many-electron ordered state (e.g., superconductivity and magnetism), and any transport experiment, requires theory beyond independent particles in a periodic potential.

A large part of our work concerns the various quantum states of strongly correlated electrons confined in zero-, one-, and two-dimensional geometries. Especially interesting are the quantum phase transitions in such systems and the dramatic manifestations of charge quantization in single-molecule and single-electron devices. Work on these problems often connects with important questions and methods in other areas of physics, especially high-energy physics and "soft" condensed matter.

Methodology: Current work in our group is generally on problems with direct experimental and even technological relevance, including collaborations with experimentalists in physics and engineering departments at Berkeley. Our approaches combine analytic techniques drawn from high-energy physics and statistical mechanics with various numerical methods.

Here are a few pictures related to old projects.

This interferometer, from Moty Heiblum's group at the Weizmann Institute, can be used to measure the phase difference between two paths of electrons around the center island. A simpler but even smaller quantum dot was used by David Goldhaber-Gordon and Marc Kastner at MIT to observe an artificial Kondo effect (the Kondo effect is caused by an exotic correlated electron state of paired spins, somewhat like superconductivity). I worked on a theory to explain some of the puzzling transport features found in this experiment: an unpaired electron on the dot forms a singlet pair with one of the electrons in the leads, but in a magnetic field this pair is gradually pulled apart, affecting the transport of electrons through the dot.

This figure is from work on the fractional quantum Hall effect. Each quantum Hall state is in some sense a different state of matter, characterized by exchange statistics which are neither fermionic nor bosonic. My former advisor, Xiao-Gang Wen, refers to this as a "quantum waltz of many". The figure shows how different quantum Hall phases, and different edge phases of the same bulk state, can be differentiated by the non-Ohmic current-voltage relationship for electron tunneling into the edge.

The more general interest of this experiment is that in one dimension interacting electrons do not form a "Fermi liquid", i.e., an adiabatic extension of a Fermi gas, but instead form a "Luttinger liquid" where the elementary excitations have zero overlap with free electrons. The edge of a 2D Hall droplet is a 1D interacting electron system in which the prediction of non-Fermi-liquid behavior has been dramatically confirmed in experiments. Luttinger liquid behavior is also observed in carbon nanotubes: some nice pictures of those are available here.

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I had a choice: either struggle and learn field theory and run the risk of blurting out some four letter word like phi^4 in Geoff's presence or simply eliminate all risk by avoiding the subject altogether. Being a great believer in the principle of least action, I chose the latter route. Like Major Major's father in Catch 22, I woke up at the crack of noon and spent eight and even twelve hours a day not learning field theory and soon I had not learnt more field theory than anyone else in Geoff's group and was quickly moving to the top.

The research described on this page is primarily supported by the National Science Foundation and US Department of Energy.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of any federal agency.

Website last updated November 1, 2004. Please direct comments to jemoore@socrates.berkeley.edu, and check back soon.