Observation of orbital ordering and origin of the nematic order in FeSe

Cao, Rongxing; Hu, Jian; Dong, Jun; Zhang, J. B.; Ye, X. S.; Xu, Yang; Чареев, Д. А.; Vasiliev, A. N.; Wu, Bing; Zeng, Xianghua; Wang, Q. L.; Wu, Guoqing

doi:10.1088/1367-2630/ab4927

Cited by 12 publications

(8 citation statements)

References 56 publications

(93 reference statements)

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“…We note that recent NMR experiments on FeSe find a dominant (≥80%) orbital contribution to the Knight shift at low temperature, in agreement with our model. 59,60 Also, the absence of any change in ΔK across the superconducting transition is consistent with an anisotropy arising from K orb and a very small K spin at low T (see Fig. 2a where our lowest data point at 1.5 K should be well below T c even for 15 T applied parallel to the planes 80 ).…”

Section: Discussionsupporting

confidence: 83%

“…Knight-shift anisotropy: experimental results When no stress is applied and the field is aligned with the Fe-Fe bonds (i.e., the orthorhombic a-or b-axis), NMR lines in the (nonmagnetic) orthorhombic phase are split into two peaks (Fig. 1a, c), in agreement with earlier studies of both LaFeAsO and FeSe 12,13,55,[59][60][61] . Upon applying uniaxial stress in both samples, the intensity of one peak grows at the expense of the other while the total intensity of the spectrum is conserved, as seen from Fig.…”

Section: Principle Of the Experimentssupporting

confidence: 89%

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Singular magnetic anisotropy in the nematic phase of FeSe

et al. 2020

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FeSe is arguably the simplest, yet the most enigmatic, iron-based superconductor. Its nematic but non-magnetic ground state is unprecedented in this class of materials and stands out as a current puzzle. Here, our nuclear magnetic resonance measurements in the nematic state of mechanically detwinned FeSe reveal that both the Knight-shift and the spin–lattice relaxation rate 1/T1 possess an in-plane anisotropy opposite to that of the iron pnictides LaFeAsO and BaFe2As2. Using a microscopic electron model that includes spin–orbit coupling, our calculations show that an opposite quasiparticle weight ratio between the dxz and dyz orbitals leads to an opposite anisotropy of the orbital magnetic susceptibility, which explains our Knight-shift results. We attribute this property to a different nature of nematic order in the two compounds, predominantly bond type in FeSe and onsite ferro-orbital in pnictides. The T1 anisotropy is found to be inconsistent with existing neutron scattering data in FeSe, showing that the spin fluctuation spectrum reveals surprises at low energy, possibly from fluctuations that do not break C4 symmetry. Therefore, our results reveal that important information is hidden in these anisotropies and they place stringent constraints on the low-energy spin correlations as well as on the nature of nematicity in FeSe.

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Section: Discussionsupporting

confidence: 83%

Section: Principle Of the Experimentssupporting

confidence: 89%

Singular magnetic anisotropy in the nematic phase of FeSe

et al. 2020

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“…The spectra were measured at several temperatures down to 2.1 K using low-power rf pulses (π/2-pulse widths up to 80µs), sweeping frequency and summing the Fourier transforms. Our results are consistent with previous reports [15][16][17][18]27], and reveal a splitting of the single 77 Se resonance below T nem = 91 K due to twinning. The resonance frequencies are given by f = γH 0 (1 + K), where γ = 8.118 MHz/T is the gyromagnetic ratio and K is the Knight shift.…”

supporting

confidence: 93%

Inhomogeneous Knight shift in vortex cores of superconducting FeSe

Vinograd,

Edwards,

Wang

et al. 2021

Preprint

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We report 77 Se NMR data in the normal and superconducting states of a single crystal of FeSe for several different field orientations. The Knight shift is suppressed in the superconducting state for in-plane fields, but does not vanish at zero temperature. For fields oriented out of the plane, little or no reduction is observed below Tc. These results reflect spin-singlet pairing emerging from a nematic state with large orbital susceptibility and spin-orbit coupling. The spectra and spin-relaxation rate data reveal electronic inhomogeneity that is enhanced in the superconducting state, possibly arising from enhanced density of states in the vortex cores. Despite the spin polarization of these states, there is no evidence for antiferromagnetic fluctuations.

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“…Recent NMR data found that anti-ferromagnetic spin fluctuations are present inside the nematic phase of FeSe 1−x S x , being strongest around x ∼ 0.1 [37]. In FeSe, spin fluctuations are rather anisotropic [37,38] and strongly field-dependent below 15 K [11]. Interestingly, the spin-fluctuations relaxation rate is enhanced below T * (Fig.…”

Section: Resultsmentioning

confidence: 94%

Anomalous high-magnetic field electronic state of the nematic superconductors FeSe1−xSx

Bristow

Reiss

Haghighirad

et al. 2020

Phys. Rev. Research

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Understanding superconductivity requires detailed knowledge of the normal electronic state from which it emerges. A nematic electronic state that breaks the rotational symmetry of the lattice can potentially promote unique scattering relevant for superconductivity. Here, we investigate the normal transport of superconducting FeSe1−xSx across a nematic phase transition using high magnetic fields up to 69 T to establish the temperature and field-dependencies. We find that the nematic state is an anomalous non-Fermi liquid, dominated by a linear resistivity at low temperatures that can transform into a Fermi liquid, depending on the composition x and the impurity level. Near the nematic end point, we find an extended temperature regime with ∼ T 1.5 resistivity. The transverse magnetoresistance inside the nematic phase has as a ∼ H 1.55 dependence over a large magnetic field range and it displays an unusual peak at low temperatures inside the nematic phase. Our study reveals anomalous transport inside the nematic phase, driven by the subtle interplay between the changes in the electronic structure of a multi-band system and the unusual scattering processes affected by large magnetic fields and disorder.Magnetic field is a unique tuning parameter that can suppress superconductivity to reveal the normal low-temperature electronic behavior of many unconventional superconductors [1,2]. High-magnetic fields can also induce new phases of matter, probe Fermi surfaces and determine the quasi-particle masses from quantum oscillations in the proximity of quantum critical points [1,3]. In unconventional superconductors, close to antiferromagnetic critical regions, an unusual scaling between a linear resistivity in temperature and magnetic fields was found [4,5]. Magnetic fields can also induce metal-toinsulator transitions, as in hole-doped cuprates, where superconductivity emerges from an exotic electronic ground state [2].FeSe is a unique bulk superconductor with T c ∼ 9 K which displays a variety of complex and competing electronic phases [6]. FeSe is a bad metal at room temperature and it enters a nematic electronic state below T s ∼ 87 K. This nematic phase is characterized by multi-band shifts driven by orbital ordering that lead to Fermi surface distortions [6,7]. Furthermore, the electronic ground state is that of a strongly correlated system and the quasiparticle masses display orbital-dependent enhancements [7,8]. FeSe shows no long-range magnetic order at ambient pressure, but complex magnetic fluctuations are present at high energies over a large temperature range [9]. Below T s , the spin-lattice relaxation rate from NMR experiments is enhanced as it captures the low-energy tail of the stripe spin-fluctuations [10,11]. Furthermore, recent µSR studies invoke the close proximity of FeSe to a magnetic quantum critical point as the muon relaxation rate shows unusual temperature dependence inside the nematic state [12].The changes in the electronic structure and magnetic fluctuations of FeSe can have profound implicatio...

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Observation of orbital ordering and origin of the nematic order in FeSe

Cited by 12 publications

References 56 publications

Singular magnetic anisotropy in the nematic phase of FeSe

Singular magnetic anisotropy in the nematic phase of FeSe

Inhomogeneous Knight shift in vortex cores of superconducting FeSe

Anomalous high-magnetic field electronic state of the nematic superconductors FeSe1−xSx

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