CAREER: Collective motion of ferroelecitric polarization in van der Waals dihalides

Nontechnical Description Two-dimensional (2D) materials are atomically thin sheets with atoms strongly bonded within each layer but weakly bonded between layers. They have unique versatility as their electronic properties can be tuned by changing the composition of a layer or stacking different 2D sheets to form heterostructures. 2D materials have shown promise for emergent technologies such as photonics and quantum computing. This project focuses on dihalides, a class of 2D materials consisting of stacked layers of transition metal ions sandwiched between halogen atoms such as such as chlorine or iodine. The dihalides being studied in this project feature coherent oscillations of electric polarization called ferrons. These oscillations occur at terahertz frequencies, which are important for imaging, communications, and ultrafast electronics. Despite their technological potential, the properties of ferrons have received little experimental attention. One challenge with such studies is the small lateral dimensions of 2D materials, which can be smaller than the millimeter wavelength of light at terahertz frequencies. This project develops near-field techniques with resolution far beyond what is possible with conventional optical studies to investigate ferrons in dihalides. The results will enhance the understanding of ferroelectricity in 2D materials and inform the development of nanophotonics and quantum electronics. The project supports a workshop to provide training in scientific communication. Such skills are needed to present scientific results from emerging research to people from all backgrounds. The workshop enhances education of scientific communication, which is central to training the future workforce and ensure U.S. leadership in quantum science. Technical Description This project investigates how ferroelectric polarization oscillations influence the nanophotonic and optoelectronic properties of van der Waals dihalides. In this project, the principal investigator develops and uses methods for near-field spectroscopy to investigate the properties of van der Waals dihalides with around ten nanometer spatial resolution at terahertz frequencies. These advances broaden the set of tools available to study resonant terahertz oscillations in van der Waals materials, which include two-dimensional materials reaching thicknesses of only a few atomic layers. Time-resolved imaging enables direct visualization of wave propagation at sub-diffraction-limited length scales in these materials. Within this project, the principal investigator uses nano-terahertz spectroscopy to study van der Waals dihalides and resolve outstanding questions on non-intuitive properties, including wave propagation below the diffraction limit. The principal investigator also develops innovative nano-terahertz methods and investigates non-linear responses of van der Waals dihalides to terahertz radiation. By studying dynamic properties of van der Waals dihalides in a deeply subwavelength operational regime, this effort deepens the understanding of how ferroelectric polarization oscillations influence optoelectronic properties of dihalides and informs the development of devices including subwavelength optical modulators. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2542045 | Program: 01002930DB NSF RESEARCH & RELATED ACTIVIT,01002627DB NSF RESEARCH & RELATED ACTIVIT,01002829DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Aaron Sternbach | Institution: University of Maryland, College Park, COLLEGE PARK, MD | Award Amount: $425,696 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2542045 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2542045.html