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Soft tilt and rotational modes in the hybrid improper ferroelectric Ca$_{3}$Mn$_{2}$O$_{7}$
- Publication Year :
- 2018
-
Abstract
- Raman spectroscopy is employed to probe directly the soft rotation and tilting modes, which are two primary order parameters predicted in the hybrid improper ferroelectric material Ca$_3$Mn$_2$O$_7$. We observe a giant softening of the 107-cm$^{-1}$ octahedron tilting mode by 26~cm$^{-1}$, on heating through the structural transition from a ferroelectric to paraelectric orthorhombic phase. This is contrasted by a small softening of the 150-cm$^{-1}$ rotational mode by 6~cm$^{-1}$. In the intermediate phase, the competing soft modes with different symmetries coexist, bringing about many-faceted anomalies in spin excitations and lattice vibrations. Our work demonstrates that the soft rotation and tilt patterns, relying on a phase-transition path, are a key factor in determining ferroelectric, magnetic, and lattice properties of Ca$_3$Mn$_2$O$_7$.<br />Comment: accepted for publication in PRB
- Subjects :
- Condensed Matter - Strongly Correlated Electrons
Subjects
Details
- Database :
- arXiv
- Publication Type :
- Report
- Accession number :
- edsarx.1803.03957
- Document Type :
- Working Paper
- Full Text :
- https://doi.org/10.1103/PhysRevB.97.094104