Hydrogen-Mediated Phase & Property Control in Rutile Oxides

Nontechnical description Modern technologies depend on materials whose electrical properties can be tuned on demand. Examples range from smart windows to computer chips that mimic the brain. This project studies a simple and gentle way to achieve such control in a family of crystals called rutile oxides. The family includes titanium dioxide, a common ingredient in paint and sunscreen. It also includes vanadium dioxide, which can switch between an insulating state and a metal-like state. The control method is called hydrogen spillover. Tiny metal particles placed on the crystal surface split hydrogen gas into single atoms. These atoms then soak into the crystal and change how well it carries electric current. Standard doping methods require high heat or harsh ion beams that damage the crystal. In contrast, this process is gentle, reversible, and works near room temperature. The research team uses this hydrogen tuning knob to turn insulators into metals, to write and erase unseen conducting paths in clear materials, and to control magnetism. These advances could lead to low-power chips that learn like the brain, clear circuits that can be rewritten, and sensors for a growing hydrogen economy. The project also strengthens Louisiana's workforce in science, technology, engineering, and mathematics (STEM). It trains a doctoral student and undergraduate researchers in crystal growth, device building, and precise electrical testing. The principal investigator also creates a new course on quantum electronics and devices for the newly re-established electrical engineering curriculum at Tulane University. Hands-on outreach brings nanoscience to middle and high school students. These efforts include a new summer camp on quantum materials run by the Tulane Science Scholars Program. A nationwide summer research initiative widens access for students across the country. Technical description This project investigates catalyst-mediated hydrogen spillover as a route to tune the quantum states of rutile transition metal oxides. The approach is general, reversible, and spatially selective. In this process, a metal catalyst splits hydrogen molecules into atoms. The atoms enter the oxide lattice as protons and travel along the open channels of the rutile structure. The protons act as structural stabilizers or as shallow donors, depending on the host. The research addresses a central open question: do hydrogen-induced metallic states arise from strong electron correlation, from disorder, or from carrier delocalization? The first objective establishes the microscopic transport physics of hydrogen-doped vanadium dioxide and titanium dioxide. These two model systems sit at opposite limits of electron correlation. Quantitative phase diagrams link hydrogen content to carrier density, mobility, effective mass, and lattice distortion. The second objective tests the generality of this mechanism in niobium dioxide, tin dioxide, and ruthenium dioxide. These studies probe suppression of structural dimerization, reversible metallic conduction in a transparent semiconductor, and chemical control of altermagnetism. Altermagnetism is a newly identified magnetic order with momentum-dependent spin splitting. The third objective converts these insights into proof-of-concept devices. Prototypes include proton-gated synaptic transistors, rewritable optical pixels, and protonic couplers that exploit phase-dependent proton diffusion. The methods combine single-crystal nanobeam and thin-film devices with stepwise hydrogen dosing. Transport studies include in situ electrical, Hall, and magnetic field measurements. Chemical and structural probes include photoelectron spectroscopy, ion mass spectrometry, Raman and infrared spectroscopy, and electron microscopy. First-principles calculations of hydrogen sites and electronic structure support the analysis. The outcome is a predictive framework that links proton uptake to emergent electronic and magnetic behavior. This framework establishes hydrogen spillover as a broad control principle for adaptive quantum materials and low-power devices. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.