Magnetic fluctuations and superconducting properties of 
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 studied by 
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 NMR

Cui, Jianying; Ding, Qing-Ping; Meier, William R.; Böhmer, Anna E.; Kong, Tai; Borisov, Vladislav; Lee, Y.; Bud’ko, Sergey L.; Valentí, Roser; Canfield, Paul C.; Furukawa, Yuji

doi:10.1103/physrevb.96.104512

Cited by 54 publications

(68 citation statements)

References 40 publications

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“…2. The observed spectra are very similar to those in the pure CaK1144 where the lower-field central peak with a greater Knight shift K (and also larger ν Q ) has been assigned to the As2 site and the higher-field central peak with a smaller K (and also smaller ν Q ) has been attributed to the As1 site [32]. Figure 3 shows the T dependence of ν Q , K ab (H ab), and K c (H c axis) for the two As sites.…”

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confidence: 69%

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NMR study of the new magnetic superconductor CaK(Fe0.951Ni0.049)4As4 : Microscopic coexistence of the he

et al. 2017

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The coexistence of a new-type antiferromagnetic (AFM) state, the so-called hedgehog spin-vortex crystal (SVC), and superconductivity (SC) is evidenced by an 75 As nuclear magnetic resonance study on singlecrystalline CaK ( Fe 0.951 Ni 0.049 ) 4 As 4 . The hedgehog SVC order is clearly demonstrated by the direct observation of internal magnetic induction along the c axis at the As1 site (close to K) and a zero net internal magnetic induction at the As2 site (close to Ca) below an AFM ordering temperature T N ∼ 52 K. The nuclear spin-lattice relaxation rate 1 / T 1 shows a distinct decrease below T c ∼ 10 K, providing also unambiguous evidence for the microscopic coexistence. Furthermore, based on the analysis of the 1 / T 1 data, the hedgehog SVC-type spin correlations are found to be enhanced below T ∼ 150 K in the paramagnetic state. These results indicate the hedgehog SVC-type spin correlations play an important role for the appearance of SC in the new magnetic superconductor.

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confidence: 69%

“…For the As1 site, with increasing T , ν Q increases from 12. The first-principles analysis shows the different T dependences of ν Q 's for the two As sites can be explained by hedgehog SVC magnetic fluctuations [32].…”

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confidence: 95%

NMR study of the new magnetic superconductor CaK(Fe0.951Ni0.049)4As4 : Microscopic coexistence of the he

et al. 2017

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“…22,23) This multiband nature implies multi-gap superconductivity in CaKFe 4 As 4 . Two superconducting gaps which are nodeless and isotropic were, indeed, observed by scanning tunneling microscopy, 20) optical conductivity, 24) penetration depth, 21) muon spin rota- * k iida@cross.or.jp tion, 18) and 75 As nuclear magnetic resonance (NMR) 25) measurements. The largest superconducting gaps (∆ hole = 13 meV and ∆ electron = 12 meV) for quasi-two-dimensional hole and electron pockets that have similar diameters at the Γ and M points were reported by ARPES studies, 22) suggesting that the ideal nesting condition with the (π, π) wave vector referred to the tetragonal reciprocal lattice.…”

Section: -9)mentioning

confidence: 88%

“…One can, therefore, expect the same spin-fluctuationmediated s ± -wave pairing mechanism 27,28) for this material, which was proposed in previous studies. [20][21][22][23]25) However, the sign of the superconducting gaps in CaKFe 4 As 4 has never been investigated via a phase-sensitive technique. As is well established, the appearance of neutron spin resonance depends sensitively on the relative signs of the superconducting gaps on different portions of the Fermi surfaces separated by momentum Q AF , and thus it serves as a direct probe of the symmetry of the superconducting order parameter.…”

Section: -9)mentioning

confidence: 99%

Spin Resonance in the New-Structure-Type Iron-Based Superconductor CaKFe₄As₄

et al. 2017

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The dynamical spin susceptibility in the new-structure-type iron-based superconductor CaKFe 4 As 4 was investigated by using a combination of inelastic neutron scattering (INS) measurements and random phase approximation (RPA) calculations. Powder INS measurements show that the spin resonance at Q res = 1.17(1) Å −1 , corresponding to the (π, π) nesting wave vector in tetragonal notation, evolves below T c . The characteristic energy of the spin resonance E res = 12.5 meV is smaller than twice the size of the superconducting gap (2∆). The broad energy feature of the dynamical susceptibility of the spin resonance can be explained by the RPA calculations, in which the different superconducting gaps on different Fermi surfaces are taken into account. Our INS and PRA studies demonstrate that the superconducting pairing nature in CaKFe 4 As 4 is the s ± symmetry.Various iron-based superconducting materials with different crystal structures have been investigated to transcend our understanding of the nature of their pairing mechanism, [1][2][3][4] as the crystal structure is believed to have a strong relationship with the superconducting transition temperature T c . 5,6) Recently, new-structure-type iron-based superconducting materials AeAFe 4 As 4 (where Ae = Ca, Sr, or Eu and A = K, Rb, or Cs) were reported. 7-9)The AeAFe 4 As 4 family exhibits T c = 32-37 K, which is relatively high compared with other stoichiometric iron-based superconductors. [10][11][12][13][14] As Ae and A layers stack alternatively between Fe 2 As 2 layers owing to the large difference between their ionic radii, AeAFe 4 As 4 belongs to the P4/mmm space group, which is different from I4/mmm in hole-doped (Ba 1−x K x )Fe 2 As 2 systems. 7, 15) AeAFe 4 As 4 has high T c at stochiometric composition and a unique crystal structure, providing us with a great opportunity to theoretically and experimentally investigate iron-based superconductivity in the absence of substitutional disorder.CaKFe 4 As 4 undergoes superconductivity below T c ≃ 35 K without other phase transitions for 1.8 ≤ T ≤ 300 K. [15][16][17] The magnetic ground state of the normal state in CaKFe 4 As 4 is paramagnetic. 16,18) Various measurements 15,16,[18][19][20][21] indicated that CaKFe 4 As 4 shows behaviors similar to optimally or slightly overdoped (Ba 1−x K x )Fe 2 As 2 . Angle-resolved photoemission spectroscopy (ARPES) measurements supported by density functional theory calculations indicated that the Fermi surface consists of three-hole pockets at the Γ point and two electron pockets at the M point. 22,23) This multiband nature implies multi-gap superconductivity in CaKFe 4 As 4 . Two superconducting gaps which are nodeless and isotropic were, indeed, observed by scanning tunneling microscopy, 20) optical conductivity, 24) penetration depth, 21) muon spin rota- * k iida@cross.or.jp tion, 18) and 75 As nuclear magnetic resonance (NMR) 25) measurements. The largest superconducting gaps (∆ hole = 13 meV and ∆ electron = 12 meV) for quasi-two-dimensional hole and electron p...

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“…Also inorganic materials can show extreme sensitivity to pressure due to formation and breaking of certain covalent bonds in their crystal structures upon pressurizing. Some examples are systems with layered ThCr 2 Si 2 (so‐called “122”) structure where the formation of a XX covalent bond (X = Si, As, Se, S, P) across the cation spacer layer at a critical pressure is accompanied by a drastic volume collapse, as is the case for the Fe‐based Ae Fe 2 As 2 and the recently discovered AeA Fe 4 As 4 families of superconductors (both structures are shown in Figure 3 where Ae and A stand for alkaline‐earth and alkali elements) where the collapse transition preserves the tetragonal lattice symmetry. A further example of pressure‐sensitive inorganic materials are layered frustrated magnets such as triangular‐lattice‐based Mott insulators Cs 2 CuCl 4 , Cs 2 CuBr 4 , and honeycomb‐lattice‐based spin‐orbit‐coupled Mott insulators α‐RuCl 3 and A 2 IrO 3 , with A = Li, Na.…”

Section: Introductionmentioning

confidence: 99%

Microscopic Modeling of Correlated Systems Under Pressure: Representative Examples

Borisov

Biswas

et al. 2019

Physica Status Solidi (b)

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The complex interplay between different order parameters in correlated systems can be finely tuned by mechanical pressure giving access to a variety of distinct phases and thereby providing new functionalities. This review addresses the challenges in the state‐of‐the‐art theoretical simulations of pressure‐induced phenomena on a few representative examples of correlated systems that are currently in the focus of on‐going contemporary research. These include organic charge‐transfer multiferroics, unconventional iron‐based superconductors, frustrated quantum magnets, and candidate systems for Kitaev physics. All these systems show pronounced structural response to moderate pressures or even structural transitions to new phases which can be successfully addressed from first principles. The simulation techniques and general trends in pressure effects are discussed for each material class.

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Magnetic fluctuations and superconducting properties of CaKFe4As4 studied by As75 NMR

Cited by 54 publications

References 40 publications

NMR study of the new magnetic superconductor CaK(Fe0.951Ni0.049)4As4 : Microscopic coexistence of the he

NMR study of the new magnetic superconductor CaK(Fe0.951Ni0.049)4As4 : Microscopic coexistence of the he

Spin Resonance in the New-Structure-Type Iron-Based Superconductor CaKFe₄As₄

Microscopic Modeling of Correlated Systems Under Pressure: Representative Examples

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Magnetic fluctuations and superconducting properties of CaKFe4As4 studied by As75 NMR

Cited by 54 publications

References 40 publications

NMR study of the new magnetic superconductor CaK(Fe0.951Ni0.049)4As4 : Microscopic coexistence of the he

NMR study of the new magnetic superconductor CaK(Fe0.951Ni0.049)4As4 : Microscopic coexistence of the he

Spin Resonance in the New-Structure-Type Iron-Based Superconductor CaKFe4As4

Microscopic Modeling of Correlated Systems Under Pressure: Representative Examples

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Product

Resources

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Spin Resonance in the New-Structure-Type Iron-Based Superconductor CaKFe₄As₄