In materials where the environment constrains their motion, conduction electrons  can cooperate to do amazing things. For example, when confined to two dimensions, electrons in strong magnetic fields can form new types of particles, with charges that are fractions of the electron charge.

In 1986, a breakthrough occurred in physics with the discovery of high temperature superconductivity, leading to tremendous scientific and technological activity worldwide.  In these stacks of copper-oxygen planes, interactions between electrons create a wealth of correlated phenomena: antiferromagnetic Mott insulator, d-wave superconductor, charge segregation, etc.

The strongest interactions are found in "heavy-fermion" materials, where electrons are slowed down so much that they act as particles with a mass up to a thousand times the electron mass.  In one material, these pair up and form a highly unconventional superconducting state with several phases, analogous to the superfluidity of helium-3.

In our new lab at Toronto, the students and research associates investigate novel materials such as heavy-fermion metals and high-temperature superconductors, by using various experimental probes.  As Ph.D. student May Chiao explains: "heat conduction is an important directional probe: we can excite low energy electrons along different directions of a single crystal and access the symmetry of the superconducting wavefunction.  It is exciting to investigate the largely unexplored properties of these electrons, which exist deep in the superconducting state.  For example, we recently demonstrated that in the high-T_c superconductor YBa₂Cu₃O₇ they exhibit universal conductivity".

"Experimental condensed matter physics is very much a hands-on research area", says Postdoctoral Associate Rob Hill. "In our studies of superconductors we need to subject samples to very extreme conditions of low temperature and high magnetic field.  In fact, our most notable results have come from performing experiments as close as possible to absolute zero. Our current studies of the vortex state will also require that we use fields approaching 20 tesla."

Much emphasis is placed on the growth of high quality single crystals and on the development of new experimental techniques -- for example, M.Sc. student Christian Lupien recently built a torque magnetometer using a piezoresistive micro-cantilever. For his Ph.D., Christian is now developing an ultrasound spectrometer, a powerful probe for anisotropic superconductors.

The group maintains active links with researchers in Canada and abroad, providing students with the possibility of joint projects, shared expertise and facilities.  Our membership in the Superconductivity Program of the Canadian Institute for Advanced Research is a considerable advantage in this respect