The Fall 2023 MatSE 590 for graduate students consists of an exciting and jam-packed schedule. MATSE 590 is a colloquium (1-3 credits) consist of a series of individual lectures by faculty, students, or outside speakers.
Graduate students will receive a weekly email with information via @psu.edu email. Graduate students are required to attend all 590 Seminars. If you have any questions, please email GradOffice@matse.psu.edu.
Program overview presented by Prof. John Mauro
CAPS (Counseling & Psychological Services)
October 12, 2023 - "Magneto-Raman Spectroscopy to Identify Spin Structure in Low-Dimensional Quantum Materials"
Angela R. Hight Walker, Senior Scientist, National Institute of Standards and Technology (NIST)
Abstract
Raman spectroscopy, imaging, and mapping are powerful non-contact, non-destructive optical probes of fundamental physics in graphene and other related two-dimensional (2D) materials, including layered, quantum materials. An amazing amount of information can be quantified from the Raman spectra, including layer thickness, disorder, edge and grain boundaries, doping, strain, thermal conductivity, magnetic ordering, and unique excitations such as magnons and charge density waves. Most interestingly for quantum materials is that Raman efficiently probes the evolution of the electronic structure and the electron-phonon, spin-phonon, and magnon-phonon interactions as a function of temperature, laser energy, and polarization. Our unique magneto-Raman spectroscopic capabilities will be detailed, enabling diffraction-limited, spatially-resolved Raman measurements while simultaneously varying the temperature (1.6 K to 400 K), laser wavelength (tunability from visible to near-infrared), and magnetic field (up to 9 T) to study the photo-physics of nanomaterials. Additionally, coupling to a triple grating spectrometer provides access to low-frequency (down to 6 cm-1, or 0.75 meV) phonon and magnon modes, which are most sensitive to coupling. Current results will be presented to highlight our capabilities and research directions, specifically on CoTiO3, a proposed Dirac topological magnon material. Interestingly, we observed a quasi-particle soup in CoTiO3: phonons, magnons, and spin-orbit excitons! We combine our experimental observations with theoretical models to explain the magnetic field dependence of all these modes. Finally, we suggest that the ring exchange of the six Co2+ within the hexagon plane is a mechanism to open a gap in the magnon spectrum at the Brillouin zone center.
Biographical Information
Dr. Hight Walker is a senior scientist at the National Institute of Standards and Technology (NIST), where she began her career as a National Research Council Postdoctoral Fellow. Her research focuses on advancing optical spectroscopies and their applicability to characterize quantum nanomaterials. Her research team has developed unique hyphenated techniques such as magneto-Raman, where samples are probed as a function of laser wavelength, temperature, magnetic field and back gating. These novel capabilities probe the underlying photophysics of nanomaterials. An issue of great importance to Angela is encouraging the young and under-resourced to participate in science. Through demonstrations and lectures, she actively engages in promoting the excitement of science. Recruiting, supporting, and mentoring students and postdoctoral researchers is a passion. Dr. Hight Walker is presently the Chair of the APS Committee on the Status of Women in Physics (CSWP).
Angela is actively involved in international documentary standards activities focused on nanotechnology, particularly the US technical committee on Measurement and Characterization to ISO TC229. Also, she is an enthusiastic member of two VAMAS committees, TWA 41 and 42, where several international round-robin studies are underway to validate measurement protocols for nanomaterials. Finally, Dr. Hight Walker leads a team composed of experts from the National Metrology Institutes concerned with enabling SI-traceable, Raman measurements.
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