Spontaneous orbital polarization in the nematic phase of FeSe

Connor A. Occhialini; Joshua J. Sanchez; Qian Song; Gilberto Fabbris; Yongseong Choi; Jong-Woo Kim; Philip J. Ryan; Riccardo Comin

doi:10.1038/s41563-023-01585-2

arXiv · 2307.10377

Spontaneous orbital polarization in the nematic phase of FeSe

Connor A. Occhialini·Joshua J. Sanchez·Qian Song·Gilberto Fabbris·Yongseong Choi·Jong-Woo Kim·Philip J. Ryan·Riccardo Comin

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Abstract

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 3d orbital occupation as a function of in situ applied stress and temperature across the nematic transition. Along with 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.

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Connor A. Occhialini, Joshua J. Sanchez, Qian Song, Gilberto Fabbris, Yongseong Choi, Jong-Woo Kim, Philip J. Ryan, Riccardo Comin. 2023-07-19. Spontaneous orbital polarization in the nematic phase of FeSe. https://doi.org/10.1038/s41563-023-01585-2

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