Materials Science Research Lecture
NOTE! Every student or postdoc (any option!) will receive a $5 SmartCash "coffee credit" for each Materials Research lecture attended, in person or online. The credits will be tallied and issued after the last speaker of the term. *If you attend in person be sure to put your name on the sign-in sheet so you are counted.
Link to join Webinar: https://caltech.zoom.us/j/85010413991
Webinar ID 850 1041 3991
Tunneling of particles is a hallmark of quantum mechanical behavior that is important for electron transport and microscopy, radioactive decay, and astrochemistry. The tunneling of atoms in the solid state is a much rarer phenomenon, which is usually discussed in the context of amorphous materials or defect behavior . Here, we will discuss the tunneling of heavy atoms in crystalline solids. Tunneling frequencies span the microwave to thermal energy range and the detection of a tunneling system typically proceeds through spectroscopic detection of the energy splitting of the two- or N-level system. The presence of two-level or N-level systems in glass is known to impact their low temperature thermal transport. Similarly, in crystalline matter, anomalous thermal transport at low-temperature is an indicator of possible tunneling behavior. Anomalously large atomic displacement parameters that increase with decreasing temperature are a second indicator. First, challenges, failure, and success, in observing atomic tunneling in thermoelectric clathrates that exhibit glass-like thermal conductivity by neutron scattering, Mössbauer spectroscopy and microwave absorption will be reviewed. Second, the investigative work that help identified atomic tunneling a hexagonal perovskite sulfide through a combination of thermal transport, neutron pair distribution function, and inelastic x-ray scattering and inelastic neutron scattering will be discussed. In this system, tunneling dynamics is observable up to room temperature and appears to have profound consequences on the thermal conductivity.
- Krumhansl J. A. Atomic Tunneling in Solids; Imry Y. The detection of Atomic Tunneling in Solids. In: Burstein, E., Lundqvist, S. (eds) Tunneling Phenomena in Solids (1969). Springer, Boston, MA.
- Hermann R. P. et al., Direct Experimental Evidence for Atomic Tunneling of Europium in Crystalline Eu8Ga16Ge30, Phys. Rev. Lett. 97, 017401 (2006). DOI: 10.1103/PhysRevLett.97.017401
- Sun B., Niu S., Hermann R. P., et al., High frequency atomic tunneling yields ultralow and glass-like thermal conductivity in chalcogenide single crystals, Nat. Commum. 11, 6039 (2020).
I gratefully acknowledge the collaboration with all colleagues. Neutron work supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES), Materials Sciences and Engineering Division. This research used resources at the Spallation Neutron Source and at the Advanced Photon Source, facilities supported by DOE, BES, Scientific User Facilities Division and at the European Synchrotron Radiation Facility, the Institute Laue-Langeving, the Paul Sherrer Institute, and DIDO at FRJ-II.
More about the Speaker:
Raphael Hermann is a Senior Researcher and lead PI of the Neutron Scattering Studies of Hybrid Excitations project in the Materials Science Division at Oak Ridge National Laboratory. He obtained his degree in physics and philosophy and his PhD in physics at the University of Liege, Belgium. He then joined The University of Tennessee as a postdoctoral researcher and then joined the Forschungszentrum Jülich in Germany where he led a Helmholtz Young Investigator Group in the Jülich Center for Neutron Science before joining Oak Ridge National Laboratory in 2015. For his research he utilizes neutron and X-ray scattering, Mössbauer and nuclear resonance techniques, and resonant ultrasound spectroscopy to study the structure and lattice dynamics in functional energy materials.