Our work seeks connections between the solid-state chemistry of materials and the physics of their functional behavior. Our synthetic capabilities range from traditional oxide synthesis to encapsulated flux growth of inorganic (sulfide, intermetallic, etc.) single crystals. We use a wide array of characterization and modeling tools to understand how our materials were formed, measure their properties, and understand new routes to engineering functionality or new synthetic techniques. Selected examples are listed below:

Tuning materials synthesis in situ

Traditional inorganic materials synthesis is often performed ex situ: the products are only examined after the reaction has completed. We use x-ray and neutron scattering and optical spectroscopy to monitor our materials synthesis reactions in situ. In addition to discovering new semiconductors on the fly, we are keenly interested in the mechanisms of how new materials form and how to control these processes.

This work is primarily supported by the US Department of Energy, Basic Energy Sciences.

Optical quantum materials

An entire ecosystem of quantum computing, networking, and storage devices will require radical new ways of storing and moving data, and optical fibers are the only reliable way to move quantum information. We are developing new materials that use rare earth ions to store optical quantum information with long coherence times. We are developing the first stable material to exhibit spectral hole-burning on a high concentration of Eu³⁺ ions, in collaboration with Prof. Elizabeth Goldschmidt.

Electronic materials driven by light and pressure

Materials with small band gaps are perched on the edge of stability, often resulting in new electronic response or structural changes upon “gentle” pressure. This pressure can come from optical excitations: our high-quality crystal growth of (TaSe₄)₂I has revealed a new narrow-band THz emission and a topological phase transitions. With pressure, we examine how the chiral semiconductors Ag₃AuSe₂ and Ag₃AuTe₂ can be tuned to have arbitrarily small band gaps, and eventually cross into a metallic state.

This work is primarily supported by the US Department of Energy, Basic Energy Sciences through the Quantum Sensing and Quantum Materials Energy Frontier Research Center.

Spin dynamics in antiferromagnets

Antiferromagnetic (AF) materials contain localized spins that are ordered below a critical temperature, like a ferromagnet, but in AFs the spins are arranged antiparallel to each other within the magnetic unit cell, giving them zero net moment. Historically, these materials have only been useful as pinning layers in magnetic data storage. However, recent reports have emerged that hint at extremely fast response of AF spins to thermal and optical stimuli, along with the possibility that electrical currents can torque the AF moments. We are investigating the fundamental spin excitation processes that occur in these materials, while also expanding the library of known metallic AF materials that show ordered spins at room temperature. Crystal growth, transport measurements, and neutron scattering are key efforts in this project.

This work is part of the Illinois MRSEC, supported by the National Science Foundation.

Discovery of new functional inorganic materials

 

New compounds with never-before-seen crystal structures can give rise to unexpected behavior that introduces new physics. These are made experimentally and the structures are usually solved from single crystals. Such compounds are often said to be obtained through serendipity, but that line of thought belies the amount of foresight required to identify a relevant material system and develop a synthesis plan. We work on new ways to identify fertile regions of phase space where new compounds are more likely to occur. Crystal growth is performed by melt and flux synthesis, vapor transport, solvothermal, hydrothermal, and solution methods.

In-situ measurements of field-assisted sintering

Processing of ceramic materials with an applied electric field is usually performed as spark plasma sintering (in a graphite die, with applied pressure) or as flash sintering (contacted by Pt electrodes, open to air). The fast Joule heating leads to unique reactions and microstructures, while the field effects near the electrode can dominate the transport behavior and lead to surprising phase equilibria. We are exploring the flash process with in-situ X-ray scattering and optical spectroscopy. This work is supported by the US Army Research Office.