One of the most intriguing phenomena in physics is superconductivity, characterized by zero electric resistance and expulsion of a magnetic field (Meissner effect). It occurs whenever an attractive interaction compels electrons to bind into pairs, which in turn form a coherent condensate below the superconducting transition temperature. In conventional superconductors such as aluminum or lead, the origin of the attractive force is well understood and stems from the interaction of electrons with the lattice vibrations - phonons. However in 1986, physicists were forced to reconsider this concept when a new class of copper-based high-temperature superconductors were discovered. Ever since, elucidating the mechanism of this unconventional superconductivity has become a primary goal of modern condensed matter physics. Several other families of unconventional superconductors have been found since, including heavy fermion materials, organic and iron-based superconductors. While the superconducting transition temperatures of some of these materials are not very high, scientists hope that understanding the origin of this phenomenon will pave way for discovering even higher-temperature superconductors relevant to technological applications.
Rice University is at the forefront of research into unconventional superconductors, with a multi-disciplinary team engaged in crystal growth, physical property characterization, optical and neutron spectroscopies, and theoretical analysis. This research ties in to the other research foci of the Center for Quantum Materials, in particular quantum criticality and strongly correlated materials. Indeed, it is believed that understanding the role of strong electron correlations in these materials is the key to explaining the origin of unconventional superconductivity. One way to induce strong electron correlations is by quantum fluctuations, which become particularly strong in the vicinity of a zero-temperature quantum phase transition into an ordered (typically magnetic) phase. Proposals have been made for existence of a quantum phase transition in high-temperature copper- and iron-based superconductors, and Rice researchers are leading theoretical and experimental efforts to understand the role of quantum criticality in the mechanism of unconventional superconductivity.