Abstract
The importance of the spin-orbit coupling (SOC) effect in Fe-based superconductors (FeSCs) has recently been under hot debate. Considering the Hund’s coupling-induced electronic correlation, the understanding of the role of SOC in FeSCs is not trivial and is still elusive. Here, through a comprehensive study of and nuclear magnetic resonance, a nontrivial SOC effect is revealed in the nematic state of FeSe. First, the orbital-dependent spin susceptibility, determined by the anisotropy of the Knight shift, indicates a predominant role from the orbital, which suggests the coexistence of local and itinerant spin degrees of freedom in the FeSe. Then, we reconfirm that the orbital reconstruction below the nematic transition temperature () happens not only on the and orbitals but also on the orbital, which is beyond a trivial ferro-orbital order picture. Moreover, our results also indicate the development of a coherent coupling between the local and itinerant spin degrees of freedom below , which is ascribed to a Hund’s coupling-induced electronic crossover on the orbital. Finally, because of a nontrivial SOC effect, sizable in-plane anisotropy of the spin susceptibility emerges in the nematic state, suggesting a spin-orbital-intertwined nematicity rather than a simple spin- or orbital-driven nematicity. The present work not only reveals a nontrivial SOC effect in the nematic state but also sheds light on the mechanism of nematic transition in FeSe.
- Received 29 April 2019
- Revised 13 December 2019
- Accepted 25 December 2019
DOI:https://doi.org/10.1103/PhysRevX.10.011034
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Electron correlation and spin-orbit coupling are two fundamental interactions in solids, which can induce many intriguing quantum matter states including superconductivity and topological phases. A compelling question is whether researchers can combine these two interactions to explore new quantum matter states. To that end, we find just such a state in an FeSe superconductor.
In iron-based superconductors, electron correlation plays a key role in the evolution of various quantum matter states. Recently, researchers have also discovered spin-orbit coupling in iron-based superconductors, which suggests this material family is a good platform to explore the interplay of electron correlation and spin-orbit coupling. Here, by using a sophisticated nuclear magnetic resonance technique, we successfully reveal a new quantum matter state in FeSe. In this state, the spin and orbital degrees of freedom are highly entangled beyond theoretical predictions. Moreover, such novel spin-orbital entanglement is directly linked to an emergent quantum effect due to the interplay of electron correlation and spin-orbit coupling.
The underlying mechanism for this new quantum matter state remains elusive. Our work will stimulate more interest in this field, and we expect that more emergent quantum effects due to the interplay of electron correlation and spin-orbit coupling will be discovered.