Jian Liu invests a magnitude of his time in very small systems. His research has won the assistant professor accolades ranging from the College of Arts and Sciences Early Career Award for Research and Creativity to a National Science Foundation CAREER award. The most recent addition to that impressive list is the Office of Naval Research (ONR) Young Investigator award, which recognizes outstanding early-career scientists to encourage their teaching and research. Liu’s is the university’s first Young Investigator award since fiscal year 2014 and only the third in the past 10 years.
Liu’s $510,000 award is sponsored by the ONR Electromagnetic Materials Program and is designated for studies on "complex oxide heterostructures for novel topological superconducting states." The advent of topological insulators in 2007 gave scientists a new realm of possibility to look for novel physics and possible applications. Topological insulators are insulators on the inside but conduct electricity on the surface, and Liu’s proposal will synthesize heterostructures that interface topology with superconductivity.
Superconductors allow current to flow with no resistance because their electrons, which normally repel each other, pair up with opposite spins. This entanglement allows the paired electrons to flip their spins at the same time, and one won’t be able to tell the difference. The orbital, as Liu explained, "is like a room for the electrons to live in and circle around." Both the spin and orbital have an angular momentum, and they may interact through spin-orbit-coupling (SOC), a relativistic effect that allows the electron spin to flip when it switches orbitals. As a result, the electron may end up with the opposite spin after it hops around and comes back to the original orbital. Because there is no way to track an individual electron, this means the electron spin can be up and down at the same time. This quantum effect is often what causes electronic topology.
To investigate this physics, Liu will create heterostructures one atomic layer at a time and then exploit their unique interplay. The strong SOC could allow for tuning the spin-pairing in superconductivity, while superconductivity could induce pairing of the spin-flipping electrons into a topological superconducting state. Liu expects his findings will be the first experimental example to merge high-temperature superconductivity and electronic topology, two key fields in condensed matter physics.
These studies are a natural progression of Liu’s research, which has delved into questions about how quantum materials respond to stress and strain as well as geometrically-frustrated quantum magnets. This latest endeavor fits well within the ONR’s Electromagnetic Materials Program, which supports work to investigate and tune the resistivity of materials, as well as innovative techniques to grow them.
Liu was one of only 25 scientists selected from more than 260 applicants for the class of 2019 awardees in the ONR Young Investigator Program. His award is supported for three years.