Orbital characters and near two-dimensionality of Fermi surfaces in NaFe1−xCoxAs

Liu, Z.-H.; Richard, P.; Li, Y.; Jia, L.-L.; Chen, G.-F.; Xia, Tian‐Long; Wang, D.-M.; He, Junbao; Yang, Heng; Pan, Zhixing K.; Valla, T.; Johnson, P. D.; Xu, N.; Ding, Hong; Wang, S.-C.

doi:10.1063/1.4767374

Cited by 9 publications

(13 citation statements)

References 26 publications

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“…In Ba(Fe 1−x Ru x ) 2 As 2 , the fact that 1/ 75 T 1 T drops due to gap formation at T N and again at T c demonstrates that additional SC electrons are present in the AFM phase 30 . By contrast, this dispersion is much weaker in the NaFe 1−x Co x As system, as shown both by ARPES studies 35,36 and by the present results (Sec. V), indicating a highly 2D system with lit-tle flexibility in Fermi-surface sizes and spanning wave vectors.…”

Section: Discussionmentioning

confidence: 30%

Phase separation, competition, and volume-fraction control inNaFe1−xCoxAs

Jia

Wang

et al. 2014

Phys. Rev. B

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We report a detailed nuclear magnetic resonance (NMR) study by combined 23 Na and 75 As measurements over a broad range of doping to map the phase diagram of NaFe1−xCoxAs. In the underdoped regime (x ≤ 0.017), we find a magnetic phase with robust antiferromagnetic (AFM) order, which we denote the s-AFM phase, cohabiting with a phase of weak and possibly proximityinduced AFM order (w-AFM) whose volume fraction V ≃ 8% is approximately constant. Near optimal doping, at x = 0.0175, we observe a phase separation between static antiferromagnetism related to the s-AFM phase and a paramagnetic (PM) phase related to w-AFM. The volume fraction of AFM phase increases upon cooling, but both the Néel temperature and the volume fraction can be suppressed systematically by applying a c-axis magnetic field. On cooling below Tc, superconductivity occupies the PM region and its volume fraction grows at the expense of the AFM phase, demonstrating a phase separation of the two types of order based on volume exclusion. At higher dopings, static antiferromagnetism and even critical AFM fluctuations are completely suppressed by superconductivity. Thus the phase diagram we establish contains two distinct types of phase separation and reflects a strong competition between AFM and superconducting phases both in real space and in momentum space. We suggest that both this strict mutual exclusion and the robustness of superconductivity against magnetism are consequences of the extreme two-dimensionality of NaFeAs.

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Section: Discussionmentioning

confidence: 30%

Phase separation, competition, and volume-fraction control inNaFe1−xCoxAs

Jia

Wang

et al. 2014

Phys. Rev. B

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“…In general H c2 is influenced by both orbital and spin-paramagnetic effects (although usually one tends to dominate), and the relative importance of these effects can be measured by the Maki parameter α = √ 2H orb c2 /H pm c2 [24,26]. Angle resolved photoemission spectroscopy measurements (ARPES) [27][28][29] and band structure calculations [30,31] show NaFe 1−x Co x As to be a quasi-two-dimensional superconductor with a Fermi surface consisting of collinear warped columns. In such systems, application of magnetic field parallel to the superconducting planes causes the electrons to form open orbits along the cylinders [32], which leads to a negligible orbital effect and significant enhancement of the orbital critical field above what would be expected for a more isotropic superconductor.…”

Section: Discussionmentioning

confidence: 99%

“…Note that this argument depends on decoupling of the band scattering rates. ARPES measurements [27] show that the hole bands are of mixed parity, while one of the electron bands is of odd parity only. This will result in a slight decoupling of the scattering times.…”

Section: B Two-band Modelmentioning

confidence: 98%

“…5(b)], which magnifies the effect of the underlying multiband nature on γ H and H ⊥ c2 . It is known that the NaFe 1−x Co x As Fermi surface consists of hole pockets at and two electron pockets on the M points of the reciprocal space; with the electron Fermi surface being slightly warped, showing a small three-dimensional component [27,28,30,31]. The Fermi surface is found to be highly sensitive to Co doping; causing the electron pockets to widen and hole pockets to shrink with doping, until the hole pockets completely vanish at x ≈ 0.1 [28].…”

Section: E Anisotropymentioning

confidence: 99%

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Upper critical field ofNaFe1−xCoxAs superconductors

et al. 2014

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The upper critical field of NaFe 1−x Co x As was measured from x = 0 to x = 0.08, with the magnetic field applied parallel (H c2 ) and normal (H ⊥ c2 ) to the planes. The data were fitted using one-band and two-band models. The orbital and paramagnetic components of the upper critical field were extracted for H c2 , which we find to be strongly dominated by paramagnetic pair breaking. In the parent compound the paramagnetic limit is equal to the value expected by BCS theory. However, substitution of Fe by Co leads to an enhancement above the BCS limit by a factor of approximately 1.6. In the overdoped region, we observe a significant convex curvature in H ⊥ c2 at low temperatures, which we attribute to the two-band nature of the superconductivity and the asymmetry between the two bands. Additionally, we discuss the behavior of critical field anisotropy, coherence length ξ , and the penetration depth λ.

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“…As is well-known, the variation of the photon energy in ARPES measurements allows one to effectively measure at different k z , and the periodic variation of the d z 2 feature is a convenient feature from which we infer appropriate photon energies for the Γ and Z points, broadly consistent with Refs. [45][46][47][48].…”

Section: Binding Energy (Mev)mentioning

confidence: 99%

Three-dimensional electronic structure of the nematic and antiferromagnetic phases of NaFeAs from detwinned angle-resolved photoemission spectroscopy

et al. 2018

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We report a comprehensive ARPES study of NaFeAs, a prototypical parent compound of the Fe-based superconductors. By mechanically detwinning the samples, we show that in the nematic phase (below the structural transition at Ts = 54 K but above the antiferromagnetic transition at TN = 43 K) spectral weight is detected on only the elliptical electron pocket along the longer a orth axis. This dramatic anisotropy is likely to arise as a result of coupling to a fluctuating antiferromagnetic order in the nematic phase. In the long-range ordered antiferromagnetic state below TN , this single electron pocket is backfolded and hybridises with the hole bands, leading to the reconstructed Fermi surface. By careful analysis of the kz variation, we show that the backfolding of spectral weight in the magnetic phase has a wavector of (π,0,π), with the c-axis component being in agreement with the magnetic ordering in NaFeAs observed by neutron scattering. Our results clarify the origin of the tiny Fermi surfaces of NaFeAs at low temperatures and highlight the importance of the three-dimensional aspects of the electronic and magnetic properties of Fe-based superconductors.The dome of unconventional superconductivity in the phase diagrams of Fe-based superconductors usually appears once the stripe antiferromagnetic order found in the parent compounds is suppressed. This proximity has inspired many works which use a spin-fluctuation pairing mechanism to explain the relatively high T c superconductivity in these materials [1,2]. However this picture is challenged by the existence of a distinct "nematic" phase in compounds such as NaFeAs, characterised by a tetragonal-orthorhombic structural transition of the lattice and twofold symmetry of the electronic structure, but without static magnetic order [3,4]. This led to some suggestions that there is a separate symmetry-breaking instability of orbital order [5], which was supported by an apparently large energy scale for d xz −d yz orbital splitting in detwinned ARPES measurements of BaFe 2 As 2 [6] and NaFeAs [7,8]. However the origin of the nematic phase is still not settled, with other groups proposing a magnetically-driven 'spinnematic' state characterised by strong antiferromagnetic fluctuations with a chosen direction but finite magnetic correlation length [9][10][11]. Thus it is important to continue to look for new insights in the parent compounds of the Fe-based superconductors, especially in systems where the nematic and magnetic phases can be distinguished such as NaFeAs.NaFeAs is a prototypical parent compound of the Fe-based superconductors, with a tetragonal-orthorhombic structural transition at T s = 54 K, and a magnetic transition at T N = 43 K. A superconducting dome reaching a maximum T c ≈ 20 K is found upon doping with Co [9, 12], Ni [13] or Rh [14] on the Fe site. While not exhibiting ordering temperatures as high as BaFe 2 As 2 (T s ≈ T N ≈ 134 K [15]) or LaFeAsO (T s ≈ 165 K, T N ≈ 145 K [16]), it offers a convenient test bed for ideas about the nematic phase due ...

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Orbital characters and near two-dimensionality of Fermi surfaces in NaFe1−xCoxAs

Cited by 9 publications

References 26 publications

Phase separation, competition, and volume-fraction control inNaFe1−xCoxAs

Phase separation, competition, and volume-fraction control inNaFe1−xCoxAs

Upper critical field ofNaFe1−xCoxAs superconductors

Three-dimensional electronic structure of the nematic and antiferromagnetic phases of NaFeAs from detwinned angle-resolved photoemission spectroscopy

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