Research Interests

Our laboratory follows a cradle-to-grave materials philosophy. Coaxing a new material into existence, rigorously testing its electronic properties, and then revealing its emergent essence through state-of-the-art measurements. We are interested in the fundamental physics of a broad range of quantum materials, from correlated f-electron intermetallics, to copper oxide and iron superconductors, to various flavors of topological materials. We utilize synthesis and basic characterization facilities at UMD and neutron facilities at NIST, working with a wide network of collaborators.

Superconductivity in UTe₂ was discovered by our group in 2018. This is an exciting find for many reasons. First, this superconducting state has a very unusual relationship with magnetic field. Very large, direction-dependent magnetic fields are necessary to destabilize the electron pairing, because the electron spins form in an uncommon spin-triplet arrangement. Moreover, this material holds the record for reentrant (comes back to life, like Lazarus) superconductivity, which exists at the highest magnetic fields of any superconductor. Second, it is becoming clear that this superconductivity is topologically nontrivial and that it supports unique surface states that may be useful for future quantum computing applications.

Generally, uranium compounds tend to exhibit unusual behavior because of the way that their 5f-electrons interact with the other electrons. This results in properties that differ dramatically from simple metals like copper or magnets like iron. Some of this behavior, generally referred to as heavy fermion or Kondo lattice, is pretty consistent and is understood, but generally, the interactions are rather complicated and remain an unsolved problem in condensed matter physics. These materials don't all follow the same rules. The uranium dipnictides such as USb₂ seem to be do things in the "wrong" order, because the f-electrons order antiferromagnetically at higher temperatures than at which they hybridize with the conduction electrons.

Topological considerations are not limited to electrons in band insulators and superconductors. Structures known as magnetic skyrmions, which are like twisted magnetic bubbles, can also have an extra stability granted by the way their component spins wind that prevents them from breaking up. This protection has been suggested to be promising for future information processing or storage applications. Skyrmion behavior in Cu₂OSeO₃ is particularly interesting because the complicated interactions provide us with different ways to tweak the magnetism through chemistry.