Spontaneous orbital polarization in the nematic phase of FeSe

The origin of nematicity in FeSe remains a critical outstanding question towards understanding unconventional superconductivity in proximity to nematic order. To understand what drives the nematicity, it is essential to determine which electronic degree of freedom admits a spontaneous order paramete...

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Bibliographic Details
Published in:Nature materials 2023-08, Vol.22 (8), p.985-991
Main Authors: Occhialini, Connor A., Sanchez, Joshua J., Song, Qian, Fabbris, Gilberto, Choi, Yongseong, Kim, Jong-Woo, Ryan, Philip J., Comin, Riccardo
Format: Article
Language:English
Subjects:
639/766/119/1003
639/766/119/995
Anisotropy
Biomaterials
Chemistry and Materials Science
Condensed Matter Physics
Critical point
Dichroism
MATERIALS SCIENCE
Nanotechnology
nematicity
NMR
Nuclear magnetic resonance
Optical and Electronic Materials
Order parameters
Phase transitions
Polarization
Spectrum analysis
strain
superconductivity
Symmetry
Unconventional superconductivity
X-ray diffraction
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Summary:The origin of nematicity in FeSe remains a critical outstanding question towards understanding unconventional superconductivity in proximity to nematic order. To understand what drives the nematicity, it is essential to determine which electronic degree of freedom admits a spontaneous order parameter independent from the structural distortion. Here we use X-ray linear dichroism at the Fe K pre-edge to measure the anisotropy of the 3 d orbital occupation as a function of in situ applied stress and temperature across the nematic transition. Along with using X-ray diffraction to precisely quantify the strain state, we reveal a lattice-independent, spontaneously ordered orbital polarization within the nematic phase, as well as an orbital polarizability that diverges as the transition is approached from above. These results provide strong evidence that spontaneous orbital polarization serves as the primary order parameter of the nematic phase. FeSe does not exhibit magnetic order and lacks a nematic quantum critical point coinciding with optimal superconductivity, suggesting that an orbital mechanism drives nematicity, but direct evidence is lacking. Here, combining X-ray linear dichroism with in situ uniaxial stress, the role of spontaneous orbital polarization in nematic-phase FeSe is determined.
ISSN:1476-1122
1476-4660
DOI:10.1038/s41563-023-01585-2