Grant: Research Tools and Instruments

Quantum materials exhibit a rich phenomenology of electronic states ranging from superconductors to correlated insulators, arising from the enormous phase space that the periodic table provides to multicomponent materials. This large phase space of materials also presents new challenges for characterization as many materials exhibit variations in crystal structure, and small changes in composition, defect density and type of defect can tip these sensitive systems into different electronic phases. This potential for inhomogeneity and extreme sensitivity to impurities makes local probe techniques that can provide high resolution spectroscopic characterization of the electronic structure an essential tool for quantum materials research. Scanning probe microscopy methods, most notably Scanning Tunnelling Microscopy and Spectroscopy (STM, STS), provide local structural and electronic characterization of surfaces on the atomic scale. With dramatic advances in instrumentation in the past 15 years, such spectroscopy measurements can now be taken at each pixel, rather than selected points, opening up access to both studies of spatial inhomogeneity of the electronic structure and a connection to the "k-space" picture that drives much of condensed matter understanding through quasiparticle interference (QPI) measurements. These measurements provide unprecedented insight into the influence of local variations in structure, charge donation, and defects, while simultaneously allowing us to measure how electrons scatter providing insight into symmetries and textures of the electronic states, such as the superconducting gap and topological features. Here, we request an SPM controller upgrade for an existing CFI-funded 1K STM/AFM system with 3T magnetic field coupled to an APRES chamber to allow for the high-quality spectroscopic measurements demanded by the Quantum Materials field, as the existing controller does not allow for the flexibility required to obtain sufficiently high-quality data to map local variations in electronic structure or produce high-quality QPI measurements needed to convincingly answer key questions in this area. Three lines of research are described, providing examples of the types of studies possible and their demands on instrumentation: Topological properties of rare-earth square net materials, Surface texture of superconductivity in a polar Fe-based superconductor, and the Search for topological superconductivity in thin films. Each requires high-spatial and energy resolution for real and/or k-space characterization of the electronic structure, and requires access to <4K temperatures and magnetic fields to explore the most exciting regimes of the electronic structures of these materials.