The properties of ferroic materials are dictated by their symmetry and, in particular, symmetry-breaking that results in transition to a phase that shows emergent behavior. Quasi-one-dimensional (1D) transition metal chalcogenides, composed of chains of face-sharing octahedra, have emerged as materials showing various ferroic order, which gives rise to properties such as colossal optical anisotropy, electronic phase transitions, and glass-like thermal conductivity.
In this presentation, I will discuss our group’s research efforts focused on studying the emergence of ferroic order in quasi-1D ATiS3 (where A = Ba, Sr) chalcogenides. I will present results showing a variety of ferroic structural distortions that ATiS3 chalcogenides can undergo, and the effect these distortions have on the optical, chiral and polar properties. We map these subtle picoscale distortions using aberration-corrected scanning transmission electron microscope (STEM)-based imaging and monochromated electron energy loss spectroscopy. We use first-principles density-functional-theory (DFT) to calculate the effect of the structural distortions on the various physical properties [1, 2]. Specifically, I will discuss: 1) ways to achieve colossal optical anisotropy in ATiS3, 2) and the realization of a new multiferroic order that combines electric polarization with chirality.
Acknowledgements: This work was primarily supported by ARO MURI grant # W911NF-21-1-0327 and NSF through DMR-2122070, DMR-2122071 and DMR-2145797. Electron microscopy work was supported by the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. This work used computational resources through allocation DMR160007 from the Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) program.
[1] H. Mei*, G. Ren *, B. Zhao*, et al. Colossal optical anisotropy from atomic-scale modulations. Advanced Materials, 2023, 2303588.
[2] B. Zhao*, G. Ren*, H. Mei, et al. Giant Modulation of Refractive Index from Picoscale Atomic Displacements. Advanced Materials (Accepted).