Nuclear magnetic resonance is a powerful method used to investigate local magnetic and electronic properties in condensed matter. However, it generally lacks the sensitivity required to study the novel states of matter that are now being discovered in thin films and interfaces. Recently we have developed a technique in which an NMR signal is detected through radioactive decay of an implanted probe nucleus. The method has roughly 10 orders of magnitude greater sensitivity than conventional NMR and is well suited to probing electronic properties of thin films, interfaces. and heterostructures. This project combines synthesis and characterization of novel oxide films and heterostructures at the MPI with investigation of their properties using beta-NMR at TRIUMF along with other complementary techniques such as resonant X-ray reflectivity [4,6], µSR and optical ellipsometry .
Application of beta NMR to transtion metal oxide heterostructures
Building on the extensive expertise in growing high quality heterostructures of transition metal oxides at the Max-Planck-Institutes, this project aims to use the unique capabilities of the low energy beam of highly polarized 8Li. Recent work shows beta-NMR can be used to study the paramagnetic metallic state  and magnetic ground states . Ongoing programs focus on the interface-related magnetism on systems actively being studied at the MPI-FKF, e.g. LaAlO3/LaNiO3 heterostructures [4,5]. We anticipate this project will expand into other perovskite heterostructures from MPI, e.g. other Nickelates, Cuprates, Cobaltates, Titanates or Manganates, all of which show great promise for exciting new physics. The main objective is to study how the interface modifies the local magnetic properties on nanometer depth scales and to search for, and characterize, the novel of states of matter that are possible in such structures.
Application of betaNMR to lithium-ion conductors
In addition, we are studying interface effects in ionic conduction in collaboration with the department of J. Maier at the MPI-FKF. Relatively little is known about the influence of heterointerfaces on ionic diffusion, despite their importance in solid state ionic devices such as Li batteries. Interfaces can induce inhomogeneous electronic/ionic modifications in the contact region, which extend over a characteristic length into the bulk. In nanosized structures, such local effects can even dominate over bulk material properties (e.g., fluoride ion conductivity in BaF2/CaF2 heterostructures ), giving rise to a mesoscopic effect. Even in simple heterostructures, an ionic interface effect can be tailored through a suitable choice of substrate . Beta NMR is uniquely suited to probe such information directly on the atomic scale[9,10]. We also have the possibility to study isolated lithium in ion conductors (e.g., electrode materials). Here, lithium is at the limit of infinite dilution, which is the experimental situation most amenable to theoretical modeling. There is opportunity with beta NMR to perform rigorous experimental tests on state-of-the-art models of lithium-diffusion, where there is extensive effort being expended.
Ongoing projects at UBC/TRIUMF beta NMR Facility
There are also projects for graduate students and postdocs centered on ongoing experiments within the beta NMR group. These include studies of topological insulators, magnetism, superconductivity, Li-battery materials, soft matter etc. Such projects could be material oriented, with betaNMR, muSR or low-energy muSR as one component of a multi-technique investigation of a new material or heterostructure. Alternatively, projects could also be technique based, studying many different samples with just one technique, in conjunction with a role in the synthesis and fabrication at a Max-Planck Institute.
- Further information about the novel technique of betaNMR can be found on the TRIUMF website under Beta NMR page, see also this recent review.
- D.L. Cortie et al., Phys. Rev. B. 91 241113 (2015)
- D.L. Cortie et al., Phys. Rev. Lett. 116 106103 (2016)
- E. Benckiser et al., Nature Materials 11, 189 (2011)
- A. V. Boris et al., Science 332, 937 (2011)
- See project #1, Resonant X-ray reflectivity
- N. Sata et al. Nature 408, 946 (2000)
- C. Li & J. Maier. Solid State Ionics 225, 408 (2012)
- J. Sugiyama et al, Phys Rev B, 96, 094402 (2017)
- R.M.L. McFadden et al, preprint
Principal investigators / Participating scientists:
Andrew MacFarlane (UBC) firstname.lastname@example.org
Rob Kiefl (UBC) email@example.com
G. Logvenov (MPI-FKF) firstname.lastname@example.org
R. Usiskin (MPI-FKF)