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Research Highlight

Colossal Anharmonic Couplings in Polar 2D Materials

Colossal Anharmonic Couplings in Polar 2D Materials
The anharmonic energy surface in meV/f.u. as a function of the fractional amplitude of the fully symmetric mode (QΓ1+ ) and the polar mode (QΓ2-). The dominant symmetry adapted distortions for the two modes in CuInP2Se6, as shown by insets (left and right).

Scientific Achievement

We develop a computational approach combining ab initio and group theoretic methods to discover and elucidate the origin of anharmonicity in polar 2D materials such as CuInP2Se6.

Significance and Impact

Results reveal that Cu-based seleno- and thio-phosphate materials belong to a completely new category of polar materials i.e., layered ferroionics, that exhibit colossal non-linearities that can be harnessed at the nano-scale for low-power microelectronic devices.

Research Details

–We combine first-principles calculations and group-theory based symmetry analysis to create model Hamiltonians by fitting the energy surface created by the distortions in the polar phase. –Hamiltonian reveals a large non-linear coupling between polar and non-polar Raman active modes.  

N. Sivadas, P. Doak, and P. Ganesh. Phys. Rev. Research, 4 013094 (2022). DOI: 10.1103/PhysRevResearch.4.013094