Unconventional superconducting gap in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="bold">NaFe</mml:mi><mml:mrow><mml:mn mathvariant="bold">0</mml:mn><mml:mo>.</mml:mo><mml:mn mathvariant="bold">95</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="bold">Co</mml:mi><mml:mrow><mml:mn mathvariant="bold">0</mml:mn><mml:mo>.</mml:mo><mml:mn mathvariant="bold">05</mml:mn></mml:mrow></mml:msub><mml:mi mathvariant="bold">As</mml:mi></mm

Liu, Z.-H.; Richard, P.; Nakayama, K.; Chen, G.-F.; Dong, Shuo; He, Junbao; Wang, D.-M.; Xia, Tian‐Long; Umezawa, Keitaro; Kawahara, T.; Souma, S.; Sato, Takafumi; Takahashi, Takashi; Qian, Tian; Huang, Yaobo; Xu, N.; Shi, Yulan; Ding, Hong; Wang, S.-C.

doi:10.1103/physrevb.84.064519

Cited by 81 publications

(54 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The gap is about 5 meV on the hole pocket and 5.4 meV on the electron pockets. Such an isotropic in-plane gap distribution has been observed before in NaFe 0:95 Co 0:05 As as well [29]. Furthermore, Fig.…”

supporting

confidence: 83%

Anisotropic but Nodeless Superconducting Gap in the Presence of Spin-Density Wave in Iron-Pnictide SuperconductorNaFe1−xCoxAs

et al. 2013

Phys. Rev. X

View full text Add to dashboard Cite

The coexisting regime of spin-density wave (SDW) and superconductivity in iron pnictides represents a novel ground state. We have performed high-resolution angle-resolved photoemission measurements on NaFe 1Àx Co x As (x ¼ 0:0175) in this regime and revealed its distinctive electronic structure, which provides some microscopic understandings of its behavior. The SDW signature and the superconducting gap are observed on the same bands, illustrating the intrinsic nature of the coexistence. However, because the SDW and superconductivity are manifested in different parts of the band structure, their competition is nonexclusive. Particularly, we find that the gap distribution is anisotropic and nodeless, in contrast to the isotropic superconducting gap observed in a SDW-free NaFe 1Àx Co x As (x ¼ 0:045), which puts strong constraints on theory. For iron-pnictide superconductors, a spin-density wave (SDW) phase appears next to the superconducting (SC) phase [5][6][7], and, in some cases, they even coexist [8][9][10][11][12][13], which gives a unique SC ground state. While the coexisting SDW and SC phases may have a significant impact on the SC mechanism [9], much is not clear about the subtle interacting nature between magnetism and superconductivity [14]. In fact, theories based on s þþ pairing symmetry suggest that there must be nodes in the SC gap in this regime [15], and the coexisting SDW and SC phases cannot be microscopic [9]. On the other hand, theories based on s þÀ pairing symmetry suggest nodeless SC gaps in the presence of weak magnetic order; moreover, the coexistence may cause angular variation of the SC gap and even give rise to nodes in the limit of strong antiferromagnetic (AFM) ordering [15,16], as indicated in a thermal conductivity study on Ba 1Àx K x Fe 2 As 2 [17].The coexistence of SDW and superconductivity in various iron pnictides has been illustrated by neutron scattering [8][9][10][11][12], nuclear magnetic resonance [18,19], and angleresolved photoemission spectroscopy (ARPES) experiments [13]. Recent scanning tunneling microscope (STM) studies show the real-space coexistence and competition of SDW and superconductivity in NaFe 1Àx Co x As [20,21]. However, so far, little is known regarding the electronic structure of the coexisting phase in the momentum space, such as its SC gap distribution, and how the two orders coexist and compete in the same electronic structure. In this paper, we report ARPES studies on NaFe 0:9825 Co 0:0175 As in this coexisting regime. The bandstructure reconstruction corresponding to the SDW formation and the SC gap could be observed on the same bands, which provides direct evidence for the intrinsic coexistence of the two orders. We find that SDW formation does not cause much depletion of the states near the Fermi energy (E F ); therefore, this formation allows the superconductivity to occur. Moreover, the SC gap distribution is found to be nodeless on all Fermi surface sheets: It is isotropic on the hole pocket, but it is highly anisotropic on the electron pocke...

show abstract

supporting

confidence: 83%

Anisotropic but Nodeless Superconducting Gap in the Presence of Spin-Density Wave in Iron-Pnictide SuperconductorNaFe1−xCoxAs

et al. 2013

Phys. Rev. X

View full text Add to dashboard Cite

show abstract

“…This form factor has been observed in two families of iron pnictides: the 122 family (such as Ba 1Àx K x Fe 2 As 2 ) [14,15,20,21] and the 111 family (such as NaFe 1Àx Co x As) [22,23]. Just like the d-wave form factor ( cosk x À cosk y ) in cuprates, such a form factor indicates that the pairing between two nextnearest-neighbor iron sites in real space dominates.…”

Section: Introductionmentioning

confidence: 87%

S4Symmetric Microscopic Model for Iron-Based Superconductors

Hao

2012

Phys. Rev. X

137

View full text Add to dashboard Cite

Although iron-based superconductors are multiorbital systems with complicated band structures, we demonstrate that the low-energy physics which is responsible for their high-T c superconductivity is essentially governed by an effective two-orbital Hamiltonian near half filling. This underlying electronic structure is protected by the S 4 symmetry. With repulsive or strong next-nearest-neighbor antiferromagnetic exchange interactions, the model results in a robust A 1g s-wave pairing which can be mapped exactly to the d-wave pairing observed in cuprates. The classification of the superconducting (SC) states according to the S 4 symmetry leads to a natural prediction of the existence of two different phases, named the A and B phases. In the B phase, the superconducting order has an overall sign change along the c axis between the top and bottom As (or Se) planes in a single Fe-As (or Fe-Se) trilayer structure, the common building block of iron-based superconductors. The sign change is analogous to the sign change in the d-wave superconducting state of cuprates upon 90 rotation. Our derivation provides a unified understanding of iron pnictides and iron chalcogenides, and suggests that cuprates and iron-based superconductors share an identical high-T c superconducting mechanism.

show abstract

“…Since the g and d bands are close to each other, we use a polynomial function to remove the large background, and we assume the background has an even symmetry with respect to E F (ref. 32). Since the BCS spectral function can be derived from the Bogoliubov formalism, it can be applied to the strong coupling regime 31,[33][34][35] .…”

Section: Methodsmentioning

confidence: 99%

Observation of strong electron pairing on bands without Fermi surfaces in LiFe1−xCoxAs

et al. 2015

Self Cite

View full text Add to dashboard Cite

In conventional BCS superconductors, the quantum condensation of superconducting electron pairs is understood as a Fermi surface instability, in which the low-energy electrons are paired by attractive interactions. Whether this explanation is still valid in high-T c superconductors such as cuprates and iron-based superconductors remains an open question. In particular, a fundamentally different picture of the electron pairs, which are believed to be formed locally by repulsive interactions, may prevail. Here we report a high-resolution angle-resolved photoemission spectroscopy study on LiFe 1 À x Co x As. We reveal a large and robust superconducting gap on a band sinking below the Fermi level on Co substitution. The observed Fermi-surface-free superconducting order is also the largest over the momentum space, which rules out a proximity effect origin and indicates that the order parameter is not tied to the Fermi surface as a result of a surface instability.

show abstract

Unconventional superconducting gap inNaFe0.95Co0.05As

Cited by 81 publications

References 35 publications

Anisotropic but Nodeless Superconducting Gap in the Presence of Spin-Density Wave in Iron-Pnictide SuperconductorNaFe1−xCoxAs

Anisotropic but Nodeless Superconducting Gap in the Presence of Spin-Density Wave in Iron-Pnictide SuperconductorNaFe1−xCoxAs

S4Symmetric Microscopic Model for Iron-Based Superconductors

Observation of strong electron pairing on bands without Fermi surfaces in LiFe1−xCoxAs

Contact Info

Product

Resources

About