We combine synchrotronbased infrared absorption and Raman scattering spectroscopies with diamond anvil cell techniques and firstprinciples calculations to explore the properties of hafnia under compression. We find that pressure drives HfO
This content will become publicly available on December 26, 2024
The discovery of the fractional quantum Hall state (FQHS) in 1982 ushered a new era of research in manybody condensed matter physics. Among the numerous FQHSs, those observed at evendenominator Landau level filling factors are of particular interest as they may host quasiparticles obeying nonAbelian statistics and be of potential use in topological quantum computing. The evendenominator FQHSs, however, are scarce and have been observed predominantly in lowdisorder twodimensional (2D) systems when an excited electron Landau level is half filled. An example is the wellstudied FQHS at filling factor
 Award ID(s):
 2104771
 NSFPAR ID:
 10502053
 Publisher / Repository:
 PNAS
 Date Published:
 Journal Name:
 Proceedings of the National Academy of Sciences
 Volume:
 120
 Issue:
 52
 ISSN:
 00278424
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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${}_{2}$ :7%Y from the mixed monoclinic ($P{2}_{1}/c$ )$+$ antipolar orthorhombic ($\mathit{Pbca}$ ) phase to pure antipolar orthorhombic ($\mathit{Pbca}$ ) phase at approximately 6.3 GPa. This transformation is irreversible, meaning that upon release, the material is kinetically trapped in the$\mathit{Pbca}$ metastable state at 300 K. Compression also drives polar orthorhombic ($Pca{2}_{1}$ ) hafnia into the tetragonal ($P{4}_{2}/nmc$ ) phase, although the latter is not metastable upon release. These results are unified by an analysis of the energy landscape. The fact that pressure allows us to stabilize targeted metastable structures with less Y stabilizer is important to preserving the flat phonon band physics of pure HfO${}_{2}$ . 
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