Department of Physics & Astronomy
University of New Mexico

OSE Seminars

Topological Band Structures Probed by NMR

Presented by Dr. Louis Bouchard, Associate Professor, UCLA Departments of Chemistry & Biochemistry and Bioengineering

In recent years, the emergence of gapless topologically protected edge states in the solid state without the need to apply an external field has led to searches for new phases of condensed matter in new and existing materials. For example, some thermoelectrics and Kondo insulators have been shown to be topological insulators (TIs). The edge states give rise to exotic phenomena include the quantum anomalous Hall effect, fractional quantum anomalous Hall effect, topological superconductor, fractional time-reversal invariance, topological crystalline insulator and the topologicalmagneto-electric effect. Because the interesting properties of TIs are found at edges and interfaces, they are challenging to study experimentally. In this talk, I will present new experimental approaches to study the electronic and magnetic properties of such topological materials based on nuclear spin interactions (namely, using nuclear magnetic resonance, NMR). Among the techniques, we shall discuss a type of radioactive ion beam spectroscopy to resolve properties as function of depth, and with nanoscale resolution. Such studies not only reveal substantial modulations of the material properties at these length scales, but also reveal new parameters such as s-d exchange integrals which cannot be obtained by other means. Because they do not rely on transport, NMR techniques may offer new and less ambiguous ways to separate bulk from surface contributions. Unlike ARPES, the method is not limited to n-type materials and one can probe p-type materials. NMR is also useful in the case of materials with high defect content even up to room temperature.

I will discuss the distinct responses of nuclear spins based on dipolar and quadrupolar moments. The new methods could have implications in the design of devices, in the search for novel physics and in the optimization of material properties

11:00 am, Thursday, November 30, 2017
Room 103, Center for High Tech Materials
Science and Technology Park - South Campus

Disability NoticeIndividuals with disabilities who need an auxiliary aid or service to attend or participate in P&A events should contact the Physics Department (phone: 505-277-2616, email: physics@unm.edu) well in advance to ensure your needs are accomodated. Event handouts can be provided in alternative accessible formats upon request. Please contact the Physics front office if you need written information in an alternative format.

A schedule of talks within the Department of Physics and Astronomy is available on the P&A web site at http://physics.unm.edu/pandaweb/events/index.php