Research in the Hallas Lab
The Importance of New Materials
Breakthroughs in condensed matter physics are often precipitated by the discovery of a new material. Sometimes a new material exhibits a never-before-seen, and never-predicted, property. This is serendipity and these types of discoveries can launch entire new fields. This was the case with the discovery of giant-magnetoresistance in thin film heterostructures and the discovery of high-temperature superconductivity in cuprates. In other realms theory outpaces experiment, as has been the case in the field of topological materials, giving rise to predicted states of matter that have not yet been observed in real materials. Here, a new material can allow connections to be drawn between theory and experiment. Testing these predictions requires crystal growers to understand the key ingredients of a theoretical model and incorporate them into a real material; translating equations into chemical elements. It is in this realm that we can use the principles of materials design, and along the way we may encounter a little serendipity.
Our Research Topics
Frustrated and Multipolar Magnets
High Entropy Materials
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 marvelous 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, x-rays, 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 resonance experiments to understand whether our magnetic material is frozen or dynamic or to determine the penetration depth in our superconductor. We also enjoy travelling to the Canadian Light Source in Saskatoon to perform x-ray scattering experiments, which can give us unique insight into the electronic states of individual elements. 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, x-ray, neutron experiments provide critical insights into the behaviors of quantum materials, that in some cases cannot be accomplished with any other experimental probe.