Orbital-driven nematicity in FeSe

Abstract

A very fundamental and unconventional characteristic of superconductivity in iron-based materials is that it occurs in the vicinity of {\it two} other instabilities. Apart from a tendency towards magnetic order, these Fe-based systems have a propensity for nematic ordering: a lowering of the rotational symmetry while time-reversal invariance is preserved. Setting the stage for superconductivity, it is heavily debated whether the nematic symmetry breaking is driven by lattice, orbital or spin degrees of freedom. Here we report a very clear splitting of NMR resonance lines in FeSe at $T_{nem}$ = 91K, far above superconducting $T_c$ of 9.3 K. The splitting occurs for magnetic fields perpendicular to the Fe-planes and has the temperature dependence of a Landau-type order-parameter. Spin-lattice relaxation rates are not affected at $T_{nem}$, which unequivocally establishes orbital degrees of freedom as driving the nematic order. We demonstrate that superconductivity competes with the emerging nematicity.

4 figures; supplementary material is included; Final version, Nature Materials, advance online publication, 10 Nov 2014

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Cited by in corpus (11)

• Iron-Based Superconductors: current status of materials and pairing mechanism
• Emergence of the nematic electronic state in FeSe
• Origin of the tetragonal-to-orthorhombic (nematic) phase transition in FeSe: a combined thermodynamic and NMR study
• Observation of two distinct $d_{xz}/d_{yz}$ band splittings in FeSe
• The origin of nematic order in FeSe
• Strong $(\pi ,0)$ spin fluctuations in $\beta$-FeSe observed by neutron spectroscopy
• Pressure-induced antiferromagnetic transition and phase diagram in FeSe
• Anomalous magnetoresistance in the spinel superconductor LiTi2O4
• Resistivity and magnetoresistance of FeSe single crystals under Helium-gas pressure
• Spin-orbital interplay and topology in the nematic phase of iron pnictides
• Orbital Nematic Order and Interplay with Magnetism in the Two-Orbital Hubbard Model