Reentrant phases in electron-doped<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>EuFe</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>As</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>: Spin glass and superconductivity

Baumgärtner, A.; Neubauer, David; Zapf, Sina; Pronin, A. V.; Jiao, Wen‐He; Cao, Guanghan; Dressel, Martin

doi:10.1103/physrevb.95.174522

Cited by 9 publications

(10 citation statements)

References 52 publications

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“…4(a). Similar observations have been reported for other iron-pnictides such as electron-doped Eu122 [25], Co-doped Ba122 [35] and Sm-1111 thin films [36]. Further theoretical effort is required to explain this behavior.…”

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confidence: 81%

“…At first glance, there is no effect of the ferromagnetic order on superconductivity of EuRbFe 4 As 4 . Indeed, unlike in Eu-122 systems, where reentrant superconductivity has been reported [25,[37][38][39], we cannot detect any indication of ordering at T N on the resistivity curve [ Fig. 1(a)] or any noticeable in-gap absorption due to vortices in IR spectra; instead, a fully developed superconducting gap and s-wave characteristic of the superfluid density is observed.…”

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confidence: 73%

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Unique interplay between superconducting and ferromagnetic orders in EuRbFe4As4

et al. 2018

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Transport, magnetic and optical investigations on EuRbFe 4 As 4 single crystals evidence that the ferromagnetic ordering of the Eu 2+ magnetic moments at T N = 15 K, below the superconducting transition (Tc = 36 K), affects superconductivity in a weak but intriguing way. Upon cooling below T N , the zero resistance state is preserved and the superconductivity is affected by the in-plane ferromagnetism mainly at domain boundaries; a perfect diamagnetism is recovered at low temperatures. The infrared conductivity is strongly suppressed in the far-infrared region below Tc, associated with the opening of a complete superconducting gap at 2∆ = 10 meV. A gap smaller than the weak coupling limit suggests the strong orbital effects or, within a multiband superconductivity scenario, the existence of a larger yet unrevealed gap.New members of the iron-pnictide family, the so-called 1144-compounds, attract interest recently because the alternating layers of alkaline A and alkaline-earth B cations produce two different kinds of As sites [1][2][3][4]. These materials can be viewed as the intergrowth of A-122 and B-122 iron-pnictides and they are naturally hole doped. The parent compounds are superconducting with transition temperatures T c around 35 K, higher than most of the 122materials; no spin-density-wave order has been observed. Among all possible candidates, Eu-based 1144-systems are even more intriguing, since the Eu-sublattice orders ferromagnetically below a critical temperature T N ≈ 15 K [5,6], similar to the 122-counterpart EuFe 2 As 2 [7-11]. Ferromagnetic order deep inside the superconducting state is very rare, in general [12,13]; hence the "ferromagnetic superconductor" EuRbFe 4 As 4 might pave the way towards realization of a "superconducting ferromagnet" [14-16]. However, the exact nature of the Eu magnetic order and its effect on superconductivity is unresolved [5, 6] because single crystals have been synthesized only recently.In this Letter we focus on the interplay between superconductivity and ferromagnetism in EuRbFe 4 As 4 single crystals. We report comprehensive investigations comprising transport, magnetic and optical measurements combined with microscopic studies of the vortex dynamics. The infrared spectra show a clear gap opening around 80 cm −1 below T c = 36 K that is slightly reduced compared to the value expected from the BCS theory. We relate this small value to the multiband character of superconductivity as well as to the depairing (orbital) effects of super-currents screening the ferromagnetic domains. A surprisingly weak effect on the superconducting condensate has been observed upon magnetic ordering indicating a rather weak interaction between Eu-and Fe-sublattices.Single crystals of EuRbFe 4 As 4 are obtained according to Ref. [4,5,17,18]; they exhibit shiny ab-faces of approximately 1 mm in size. The structure of the compound is presented in Fig. 1(a). The crystals are characterized by x-ray, electrical transport, and magnetic susceptibility measurements. In Fig. 1(a) we plot the dc ...

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confidence: 81%

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confidence: 73%

Unique interplay between superconducting and ferromagnetic orders in EuRbFe4As4

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“…So far, there is no experimental evidence about the sign-changing superconductivity in Eu-containing ironbased superconductors, which can demonstrate that Eucontaining iron-based superconductors also belong to the same paradigm as other iron-based superconductors in spite of the local magnetic moments of Eu 2+ between FeAs layers. Moreover, there is a longstanding issue about the possible interplay between the long-range magnetic order of Eu 2+ local moments and the superconductivity of the FeAs layer in the Eu-containing iron-based superconductors 18,41,[44][45][46][47][48][49][50][51][52][53] . It is, therefore, important to report such coupling in the case of EuRbFe 4 As 4 since EuRbFe 4 As 4 contains no substitutional disorder.…”

Section: Introductionmentioning

confidence: 99%

Coexisting spin resonance and long-range magnetic order of Eu in EuRbFe4As4

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Magnetic excitations and magnetic structure of EuRbFe4As4 were investigated by inelastic neutron scattering (INS), neutron diffraction, and random phase approximation (RPA) calculations. Below the superconducting transition temperature Tc = 36.5 K, the INS spectra exhibit the neutron spin resonances at Qres = 1.27(2)Å −1 and 1.79(3)Å −1 . They correspond to the Q = (0.5, 0.5, 1) and (0.5, 0.5, 3) nesting wave vectors, showing three dimensional nature of the band structure. The characteristic energy of the neutron spin resonance is Eres = 17.7(3) meV corresponding to 5.7(1)kBTc. Observation of the neutron spin resonance mode and our RPA calculations in conjunction with the recent optical conductivity measurements are indicative of the s± superconducting pairing symmetry in EuRbFe4As4. In addition to the neutron spin resonance mode, upon decreasing temperature below the magnetic transition temperature TN = 15 K, the spin wave excitation originating in the long-range magnetic order of the Eu sublattice was observed in the low-energy inelastic channel. Single-crystal neutron diffraction measurements demonstrate that the magnetic propagation vector of the Eu sublattice is k = (0, 0, 0.25), representing the three-dimensional antiferromagnetic order. Linear spin wave calculations assuming the obtained magnetic structure with the intra-and interplane nearest neighbor exchange couplings of J1/kB = −1.31 K and Jc/kB = 0.08 K can reproduce quantitatively the observed spin wave excitation. Our results show that superconductivity and longrange magnetic order of Eu coexist in EuRbFe4As4 whereas the coupling between them is rather weak.

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“…4(g) and 4(i) for low fields along the c and a axes, respectively. In most doped EuFe 2 As 2 materials, particularly in in-plane fields 10,11,[20][21][22] , the material does not exhibit full diamagnetism in the superconducting state, only a diamagnetic shift on top of a large paramagnetic background. In general, a field-trained difference can be explained by either the freezing-in of magnetic moments or by superconductivity with vortex pinning.…”

Section: Resultsmentioning

confidence: 99%

“…A hump at 12-14 K in the in-plane susceptibility at low fields in P-and Ir-doped material 10,30 has been attributed to a spin-glass transition below the antiferromagnetic transition in analogy to EuFe 2 P 2 . The picture here is that the c-axis-aligned ferromagnetic moments have a disordered ab-plane component driven by antiferromagnetic interlayer RKKY interactions, and this inplane component freezes.…”

Section: Resultsmentioning

confidence: 99%

Electronic structure and H−T phase diagram of Eu(Fe1−xRhx)<

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The iron-based superconductors represent a promising platform for high-temperature superconductivity, but the interactions underpinning their pairing present a puzzle. The EuFe2As2 family is unique among these materials for having magnetic order which onsets within the superconducting state, just below the superconducting transition. Superconductivity and magnetic order are normally antagonistic and often vie for the same unpaired electrons, but in this family the magnetism arises from largely localized Eu moments and they coexist, with the competition between these evenly-matched opponents leading to reentrant superconducting behavior. To help elucidate the physics in this family and the interactions between the magnetic order and superconductivity, we investigate the H-T phase diagram near optimal Rh doping through specific heat, resistivity, and magnetization measurements, and study the electronic structure by angular-resolved photoemission spectroscopy. The competition between the Eu and FeAs layers may offer a route to directly accessing the electronic structure under effective magnetic fields via ARPES, which is ordinarily a strictly zero-field technique. arXiv:1905.11554v2 [cond-mat.supr-con]

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Reentrant phases in electron-dopedEuFe2As2: Spin glass and superconductivity

Cited by 9 publications

References 52 publications

Unique interplay between superconducting and ferromagnetic orders in EuRbFe4As4

Unique interplay between superconducting and ferromagnetic orders in EuRbFe4As4

Coexisting spin resonance and long-range magnetic order of Eu in EuRbFe4As4

Electronic structure and H−T phase diagram of Eu(Fe1−xRhx)<

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