Condensed matter physics explores the emergent properties of matter at macroscopic scales. In the Shen group, we are especially interested in understanding the fascinating properties of quantum materials, for which semiclassical treatment is not sufficient and quantum effects play an important role.
An important class of quantum materials are strongly correlated electron systems. They exhibit exotic electronic and magnetic properties that cannot be sufficiently accounted for by non-interacting properties of their individual constituents. Amongst naturally occurring compounds, the transition metal oxides (with partially filled d or f electron shells and narrow bandwidths) mostly belong to this class. The simple picture of a non-interacting electron gas no longer applies for these materials, as the strong Coulomb interaction experienced by electrons is non-perturbative and hardly negligible. The most studied example of strong electron correlation are the copper oxides (cuprates), which exhibit unconventional superconductivity with high transition temperatures due to mechanisms whose nature are unresolved and remain under intense debate today. Other remarkable strongly correlated phenomena include iron-based superconductivity (FeSC), colossal magnetoresistance, heavy fermions, Mott insulators, the Kondo effect, and spin-charge ordering.