Emergent Ground State Behavior in Materials with Strongly Coupled Order Parameters
Professor MacDougall explores novel states of matter in quantum materials using advanced instrumentation housed at national laboratories to examine large single crystals grown in his labs. By using both neutron scattering and muon spin rotation (μSR), his research group is able to study magnetic correlations, volume fractions, collective excitations and superconducting phases in materials of interest. He uses these techniques to identify and understand the origins of novel phases, in an effort to generalize to other material systems.
There are two parallel efforts: 1) the study of new magnetic phases seeded by strong spin-lattice coupling, and 2) the study of intertwined charge, spin and superconducting order parameters in correlated electron materials. A major example of the former is the observation of spontaneous phase separation in the material Mn3O4 at low temperatures into ordered and disordered volumes, and the ordering of order-disorder domain walls on an emergent length scale of d~100nm. Professor MacDougall’s research group is currently exploring the generality of this effect and the possibility of using it to control material properties in a way analogous to `colossal’ response functions in rare-earth manganates.
The group’s studies of superconductivity focus on materials containing co-existing superconducting, spin and charge orders, and explore the possibility that phase-sensitive coupling terms in the free energy could seed novel `pair density wave’ (PDW) states. The existence of such a phase could explain key experimental observations in the high-temperature cuprate superconductors, and other materials, and could further stabilize other unconventional superconducting signatures such as half-quantized vortices. Professor MacDougall is part of a multi-investigator team which is seeking to experimentally verify these signatures in various PDW candidates and establish the veracity and generality of the theory.