Observation of Multiple Gap Structures Using NdFeAsO1−x F x –GaAs Tunneling Junction

Tanaka, Masashi; Shimada, Daisuke

doi:10.1007/s10948-010-0869-7

Cited by 13 publications

(14 citation statements)

References 20 publications

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“…The latter value exceeds the weak-coupling BCS limit 3.52 and points to a strong electron-boson coupling. The value obtained is close to those determined for 1111 oxypnictides by PCAR spectroscopy [49][50][51] , nuclear magnetic resonance 52 , and scanning tunneling microscopy 17 . The BCS-ratio for the small gap 2∆ S /k B T local C = 1.1-1.6 lies well below the BCS-limit, obviously, because T local C ≫ T S C .…”

Section: E Summary Of the Datasupporting

confidence: 84%

Evolution of superconducting gaps in Th-substituted Sm1−xThxOFeAs studied by multiple Andreev reflection spectroscopy

et al. 2017

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Using intrinsic multiple Andreev reflections effect (IMARE) spectroscopy, we studied SnS contacts in the layered oxypnictide superconductors Sm1−xThxOFeAs with various thorium doping and critical temperatures TC = 21-54 K. We observe a scaling between both superconducting gaps and TC. The determined BCS-ratio for the large gap 2∆L/kBTC = 5.0-5.7 and its eigen BCS-ratio (in a hypothetical case of zero interband coupling) 2∆L/kBT L C = 4.1-4.6 both exceeding the weakcoupling limit 3.52, and for the small gap 2∆S/kBTC = 1.2-1.6 remain nearly constant within all the TC range studied. The temperature dependences ∆L,S(T ) agree well with a two-band BCS-like Moskalenko and Suhl model. We prove intraband coupling to be stronger than interband coupling, whereas and Coulomb repulsion constants µ * are finite in Sm-based oxypnictides.

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Section: E Summary Of the Datasupporting

confidence: 84%

Evolution of superconducting gaps in Th-substituted Sm1−xThxOFeAs studied by multiple Andreev reflection spectroscopy

et al. 2017

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“…Therefore, we compare in Table 1 our data for Gd-1111 with other data available for Sm-, Nd-and Tb-1111 superconductors with similar T c . We emphasize rather good agreement between 2∆ L /k B T c values determined from our study and those from STS [21], break-junction measurements [33], and some PCAR-measurements [22,[38][39][40].…”

supporting

confidence: 79%

“…In particular, similar situation is believed to be realized in MgB 2 [30] and LaO 0.9 F 0.1 FeAs [31]. The presence of the large superconducting gap characterized by 2∆ L /k B T c > 3.52 in the 1111-family compounds REOFeAs (RE = La, Sm, Nd) was confirmed by tunneling spectroscopy using break-junction technique [33], point-contact Andreev reflection spectroscopy [20,22,[35][36][37][38][39][40], scanning tunneling spectroscopy [21,33], and angle-resolved photoemission spectroscopy (ARPES) [34] (see Table 1). To the best of our knowledge, there is no other available data for Gd-1111.…”

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confidence: 99%

Observation of multi-gap superconductivity in GdO(F)FeAs by Andreev spectroscopy

et al. 2011

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We have studied current-voltage characteristics of Andreev contacts in polycrystalline GdO0.88F0.12FeAs samples with bulk critical temperature Tc = (52.5 ± 1) K using break-junctions technique. The data obtained cannot be described within the single-gap approach and suggests the existence of a multi-gap superconductivity in this compound. The large and small superconducting gap values estimated at T = 4.2K are ∆L = 10.5 ± 2 meV and ∆S = 2.3 ± 0.4 meV, respectively.

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“…In other words, the edge energy ∆ changes into (∆ + ε 0 ) for some electrons, where ε 0 < 2∆ is a particular boson energy. In Nd-1111, the Eliashberg function extracted from d 2 I(V)/dV 2 [14] well matches the calculated one, and the phonon density of states [44]. Scanning tunneling spectroscopy (STS) studies with Ba 0.6 K 0.4 Fe 2 As 2 revealed a fine structure attributed to a coupling of quasiparticles with a bosonic mode near 14 meV [43].…”

supporting

confidence: 69%

Evidence of a multiple boson emission in Sm _1−x Th _x OFeAs

Kuzmichev

Kuzmicheva

Zhigadlo

2017

EPL

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-We studied a reproducible fine structure observed in dynamic conductance spectra of Andreev arrays in Sm1−xThxOFeAs superconductors with various thorium concentrations (x = 0.08-0.3) and critical temperatures Tc = 26-50 K. This structure is unambiguously caused by a multiple boson emission (of the same energy) during the process of multiple Andreev reflections. The directly determined energy of the bosonic mode reaches ε0 = 14.8 ± 2.2 meV for optimal compound. Within the studied range of Tc, this energy as well as the large ∆L and the small ∆S superconducting gaps, nearly scales with critical temperature with the characteristic ratio ε0/kBTc ≈ 3.2 (and 2∆L/kBTc ≈ 5.3, correspondingly) resembling the expected energy ∆L + ∆S of spin resonance and spectral density enhancement in s ± and s ++ states, respectively.Fe-based superconductors Sm 1−x Th x OFeAs belong to the oxypnictide family (so called 1111), and have rather simple crystal structure, resembling the stack of superconducting FeAs blocks alternating with Sm 1−x Th x O spacers along the c-direction [1]. Under electron doping, the T c varies in the wide range, reaching 54 K at x ≈ 0.3 nominal concentration [1,2]. Band-structure calculations [3] showed the density of states at the Fermi level formed mainly by iron 3d states. For this reason, the (Sm,Th) substitution affecting the spacer structure barely seems not changing the underlying pairing mechanism [4]. The Fermi surface consists of tubular sections, electron-like near the M point of the first Brillouin zone, and hole-like near the Γ point, both with no significant k z anisotropy [3,5].The majority of theoretical and experimental studies [3][4][5][6][7][8] suppose two superconducting condensates developing below T c . Earlier we reported the scaling between both gaps (∆ L -large gap, ∆ S -small gap) and T c , keeping 2∆ S /k B T c ≈ 1.2 − 1.6 and 2∆ L /k B T c = 5. 0−5.7 [4,9-11]. Similar 2∆ L /k B T c was obtained in literature for Sm-1111 in point-contact probes [12,13], and for various other 1111 [14][15][16][17][18][19][20]. Both BCS-ratios diverge from the weakcoupling BCS prediction due to a strong coupling in the "driving" bands where the large gap is developed, and a k-space proximity effect with the "driven" ∆ S bands. The pairing p-1

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Observation of Multiple Gap Structures Using NdFeAsO1−x F x –GaAs Tunneling Junction

Cited by 13 publications

References 20 publications

Evolution of superconducting gaps in Th-substituted Sm1−xThxOFeAs studied by multiple Andreev reflection spectroscopy

Evolution of superconducting gaps in Th-substituted Sm1−xThxOFeAs studied by multiple Andreev reflection spectroscopy

Observation of multi-gap superconductivity in GdO(F)FeAs by Andreev spectroscopy

Evidence of a multiple boson emission in Sm _1−x Th _x OFeAs

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Observation of Multiple Gap Structures Using NdFeAsO1−x F x –GaAs Tunneling Junction

Cited by 13 publications

References 20 publications

Evolution of superconducting gaps in Th-substituted Sm1−xThxOFeAs studied by multiple Andreev reflection spectroscopy

Evolution of superconducting gaps in Th-substituted Sm1−xThxOFeAs studied by multiple Andreev reflection spectroscopy

Observation of multi-gap superconductivity in GdO(F)FeAs by Andreev spectroscopy

Evidence of a multiple boson emission in Sm 1−x Th x OFeAs

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Evidence of a multiple boson emission in Sm _1−x Th _x OFeAs