Superconducting order parameter and bosonic mode in hydrogen-substituted 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>NdFeAsO</mml:mi><mml:mrow><mml:mn>0.6</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mrow><mml:mn>0.36</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>
 revealed by multiple-Andreev-reflection spectroscopy

Despite several theoretical approaches describing multiple Andreev reflections (MAR) effect in superconductor-normal metal-superconductor (SNS) junction are elaborated, the problem of comprehensive and adequate description of MAR is highly actual. In particular, a broadening parameter Γ is still unaccounted at all, whereas a ballistic condition (the mean free path for inelastic scattering l to the barrier width d ratio) is considered only in the framework of Kümmel, Gunsenheimer, and Nikolsky (KGN), as well as Gunsenheimer-Zaikin approaches, for an isotropic case and fully-transparent constriction. Nonetheless, an influence of l/d ratio to the dynamic conductance spectrum (dI/dV) features remains disregarded, thus being one of the aims of the current work. Our numerical calculations in the framework of an extended KGN approach develop the l/d variation to determine both the number of the Andreev features and their amplitudes in the dI/dV spectrum. We show, in the spectrum of a diffusive SNS junction (l/d → 1) a suppression of the Andreev excess current, dramatic change in the current voltage I(V)-curve slope at low bias, with only the main harmonic at eV = 2∆ bias voltage remains well-distinguished in the dI/dV-spectrum. Additionally, we attempt to make a first-ever comparison between experimental data for the high-transparency SNS junctions (more than 85 %) and theoretical predictions. As a result, we calculate the temperature dependences of amplitudes and areas of Andreev features within the extended KGN approach, which qualitatively agrees with our experimental data obtained using a "break-junction" technique.

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“…1). Typically this is the case for polycrystalline sample of layered compound as well 9,[20][21][22] .…”

Section: Model and Methodsmentioning

confidence: 99%

Amplitudes of minima in dynamic conductance spectra of the SNS Andreev contact

Popović

Kuzmichev

Kuzmicheva

2020

Journal of Applied Physics

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“…These compounds, which belong to the 1111 family of Fe-based superconductors, exhibit a ZrCuSiAs-type structure, composed of alternating stacks of LnO and FeAs layers. They become superconductors either through chemical substitution at different atomic sites, or through the application of external pressure [2][3][4]. Consequently, the resulting electronic phase diagrams depend sensitively on the particular doping element.…”

Section: Introductionmentioning

confidence: 99%

“…In particular, it has been shown that the LnFeAsO parent compounds can be doped with holes by partially replacing the Ln 3+ ions with divalent ions, such as Sr 2+ , as, e.g., in La 1−x Sr x FeAsO [5] or Pr 1−x Sr x FeAsO [6]. In contrast, n-type doping can be achieved by substituting Ln 3+ with tetravalent ions, such as Th 4+ (Sm 1−x Th x FeAsO) [7,8], or by partially replacing O 2− with F − or H − (LnFeAsO 1−x F x , LnFeAsO 1−x H x ) [2,3]. In addition, in the case of isovalent doping of the Ln1111 parent compound, as, e.g., in the As 1−x P x case, one can tune the magnetic interactions without changing the carrier concentration [9,10].…”

Section: Introductionmentioning

confidence: 99%

Superconductivity of underdoped PrFeAs(O,F) investigated via point-contact spectroscopy and nuclear magnetic resonance

Daghero

Piatti²,

Zhigadlo³

et al. 2020

Phys. Rev. B

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Underdoped PrFeAs(O,F), one of the lesser known members of the 1111 family of iron-based superconductors, was investigated in detail by means of transport, magnetometry, nuclear magnetic resonance (NMR) measurements, and point-contact Andreev-reflection spectroscopy (PCARS). PCARS measurements on single crystals evidence the multigap nature of PrFeAs(O,F) superconductivity, shown to host at least two isotropic gaps, clearly discernible in the spectra, irrespective of the direction of current injection (i.e., along the ab planes or along the c axis). Additional features at higher energy can be interpreted as signatures of a strong electronboson coupling, as demonstrated by a model which combines Andreev reflection with the Eliashberg theory. Magnetic resonance measurements in the normal phase indicate the lack of a magnetic order in underdoped PrFeAs(O,F), while 75 As NMR spin-lattice relaxation results suggest the presence of significant electronic spin fluctuations, peaking above T c and expected to mediate the superconducting pairing.

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“…These compounds, which belong to the 1111 family of Fe-based superconductors, exhibit a ZrCuSiAs-type structure, composed of alternating stacks of LnO and FeAs layers. They become superconductors either through chemical substitution at the different atomic sites, or through the application of external pressure [2][3][4] . Consequently, the resulting electronic phase diagrams depend sensitively on the particular doping element.…”

Section: Introductionmentioning

confidence: 99%

“…in La 1−x Sr x FeAsO 5 or Pr 1−x Sr x FeAsO 6 . By converse, n-type doping can be achieved by substituting Ln 3+ with tetravalent ions, such as Th 4+ (Sm 1−x Th x FeAsO) 7,8 , or by partially replacing O 2− with F − or H − (LnFeAsO 1−x F x , LnFeAsO 1−x H x ) 2,3 In addition, in case of isovalent doping of the Ln1111 parent compound, as e.g., in the As 1−x P x case, one can tune the magnetic interactions without changing the carrier concentration 9,10 . Until now, the electron-doped Ln1111-type oxypnictides (O 1−x F x and O 1−x H x ) seem to exhibit the highest T c 's.…”

Section: Introductionmentioning

confidence: 99%

Superconductivity of underdoped PrFeAs(O,F) investigated via point-contact spectroscopy and nuclear magnetic resonance

Daghero,

Piatti,

Zhigadlo

et al. 2020

Preprint

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Underdoped PrFeAs(O,F), one of the less known members of the 1111 family of iron-based superconductors, was investigated in detail by means of transport, SQUID magnetometry, nuclear magnetic resonance (NMR) measurements and point-contact Andreev-reflection spectroscopy (PCARS). PCARS measurements on single crystals evidence the multigap nature of PrFeAs(O,F) superconductivity, shown to host at least two isotropic gaps, clearly discernible in the spectra, irrespective of the direction of current injection (i.e., along the a b planes or along the c axis). Additional features at higher energy can be interpreted as signatures of a strong electron-boson coupling, as demonstrated by a model which combines Andreev reflection with the Eliashberg theory. Magnetic resonance measurements in the normal phase indicate the lack of a magnetic order in underdoped PrFeAs(O,F), while 75 As NMR spin-lattice relaxation results suggest the presence of significant electronic spin fluctuations, peaking above T c and expected to mediate the superconducting pairing.

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Superconducting order parameter and bosonic mode in hydrogen-substituted NdFeAsO0.6H0.36 revealed by multiple-Andreev-reflection spectroscopy

Cited by 11 publications

References 47 publications

Amplitudes of minima in dynamic conductance spectra of the SNS Andreev contact

Amplitudes of minima in dynamic conductance spectra of the SNS Andreev contact

Superconductivity of underdoped PrFeAs(O,F) investigated via point-contact spectroscopy and nuclear magnetic resonance

Superconductivity of underdoped PrFeAs(O,F) investigated via point-contact spectroscopy and nuclear magnetic resonance

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