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Materials innovations have sparked most of the major technological advances across the millennia – from the stone, bronze, and iron ages through to the current silicon age. Science now stands on the precipice of a new era: the age of quantum materials – materials with extraordinary electronic and magnetic properties that rely on quantum mechanical effects. In the Hallas group, we use state-of-the-art crystal growth techniques to discover new quantum materials that could unlock these future technologies.
Crystal growth of new materials
Our group uses a wide range of synthetic methods to grow samples of the materials we study. Conventional solid state methods (shake-and-bake) and flux crystal growth are ideally suited to exploratory synthesis in the pursuit of exciting new materials. The optical floating zone image furnace is a powerful tool that allows us to grow pristine large single crystals. High pressure methods allow us to capture metastable phases that cannot be grown under ambient pressure conditions, an excellent route to finding new structural phases with the potential for exotic new properties. By using this diverse set of synthetic techniques, we are able to explore the periodic table in an unconstrained way, applying the most favourable method for the material we seek to grow.
Structure and the role of disorder
Understanding the crystallography of our new material provides the foundation upon which all other characterizations rest. First and foremost, the crystal symmetry and the connectivity of our lattice informs which theoretical models may be applicable to our material. Furthermore, it is often the materials with the most interesting ground states that exhibit the most profound sensitivity to disorder. Thus, it is crucial to determine what types of disorder are present, and attempt to modify the crystal growth recipe to obtain the highest quality samples. To accomplish these structural characterizations, our starting point is always x-ray diffraction. From there on, we can expand to other tools such as neutron diffraction and electron microscopy.
Magnetic and electronic phenomena
Quantum materials can have remarkable magnetic and electronic states, ranging from superconductors to spin liquids to topological semimetals. These states often emerge under extreme conditions, very low temperatures and high magnetic fields. We have the ability to measure a wide range of physical properties, including magnetic susceptibility, heat capacity, and electrical resistivity, down to 0.05 K (1/20th of a degree above absolute zero!) and magnetic fields up to 14 T.
Seeing deeper with neutrons and muons
While we can perform many measurements in our very own lab, some experimental techniques require us to travel to beam lines at large user facilities. We are lucky that Canada's only muon source, TRIUMF, is conveniently located on UBC campus. We can use muon spin relaxation experiments to understand whether our magnetic material is frozen or dynamic or to determine the penetration depth in our superconductor. To access neutron beams we have to travel further; Canada does not currently have a major neutron source. Neutron scattering experiments can tell us the arrangement of magnetic moments in a magnetically ordered material or to map out the the spin excitations. Muon and neutron experiments provide critical insights into the behaviors of quantum materials, that in some cases cannot be accomplished with any other experimental probe.
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