Tuning crystal symmetries by out-of-plane shear deformation

Crystal structure plays a critical role in how emergent electronic states form in quantum materials, and this has motivated a growing interest in deforming crystals while measuring their electronic properties. The most straightforward way of accomplishing this is via mechanical strain—by mechanically deforming a crystallite, crystal parameters and symmetries can be tuned and their impact on material properties can be observed. To date, valuable insights have been gained by controlling in-plane strain using piezoelectric elements to stretch or compress a crystal while measuring its electronic transport behavior. On the other hand, out-of-plane strain—accomplished by shearing a crystal—is largely unexplored, but would enable us to study superconductivity, ferroelectricity, topology, and magnetism in new ways. Here I will discuss our efforts to perform out-of-plane shear-based measurements. To this end, we have developed multiple shearing methods based on (1) low temperature scanning probes and (2) a homebuilt "shear cell" that can be inserted inside commercial cryostats/fridges. We will discuss these methods' ability to explore stacking-dependent magnetism in chromium trihalides and phase transitions in iron-based superconductors.