Evidence for a two-band behavior of MgB2 from point-contact and tunneling spectroscopy

Ponomarev, Y.-A. G.; Kuzmichev, S. A.; Mikheev, M. G.; Sudakova, M. V.; Tchesnokov, S. N.; Timergaleev, N. Z.; Yarigin, A.V.; Maksimov, Evgenii G.; Krasnosvobodtsev, S. I.; Varlashkin, A. V.; Hein, Matthias; Müller, Günter; Piel, H.; Sevast’yanova, L. G.; Kravchenko, O. V.; Burdina, K. P.; Булычев, Б. М.

doi:10.1016/j.ssc.2003.09.024

Cited by 74 publications

(31 citation statements)

References 25 publications

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“…Similar energy was obtained in tunneling SIS contact studies, extracted from a fine structure caused by a resonant excitation of Leggett plasmons mode by Josephson supercurrent [39,40]. According to theory [56], that energy was not exceeded the doubled small gap, and evolved as ω 2 L ∼ ∆ σ · ∆ π within nearly full range of aluminum concentration and T c = 6 − 41 K [39,40]. Here in Sm-1111, we reproducibly observe up to k = 4 equidistant satellites, which evidences their bosonic origin.…”

supporting

confidence: 73%

“…More recent theoretical studies showed that in framework of both s ++ and s ± models the dynamic spin susceptibility has a feature near ∆ L + ∆ S energy, a sharp peak related to spin resonance in s ± state, or spectral density enhancement above ∆ L + ∆ S in s ++ state [25,32]. Tunneling contact probes could provide information about electron-boson interaction [33][34][35][36][37][38][39][40][41][42][43]. For tunneling normal metal -insulator -superconductor (NIS) junction, the derivative d 2 I/dV 2 of dynamic conductance spectrum at bias voltages V > ∆/e represents a spectral function of electron-boson interaction [41].…”

mentioning

confidence: 99%

“…Boson absorption is nearly impossible, due to the lack of excited bosons at low temperatures. When the bosonic mode has a particular energy ε 0 , one should observe satellite dips beyond the SGS at bias voltages [34,39,40,48] …”

mentioning

confidence: 99%

“…(6) Unlike magnesium diborides [39,40], one cannot attribute the observed bosonic mode as Leggett plasma mode [56]. Firstly, several theoretical studies shown that Leggett plasmons are unobservable in iron pnictides [62,63].…”

mentioning

confidence: 99%

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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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supporting

confidence: 73%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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

Kuzmichev

Kuzmicheva

Zhigadlo

2017

EPL

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“…It has been claimed that the Leggett mode has been observed in MgB 2 by Raman scattering 49 and point-contact transport measurements, 50 although the energies of the Leggett mode measured in the two experiments are different. Reference 51 found that in the weak-coupling treatment of superconductors with an s Ϯ gap, however, the A 1g Leggett mode does not couple to Raman scattering.…”

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confidence: 98%

Leggett mode in a strong-coupling model of iron arsenide superconductors

Burnell

Parish

et al. 2010

Phys. Rev. B

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Using a two-orbital model of the superconducting phase of the pnictides, we compute the spectrum of the Leggett mode-a collective excitation of the phase of the superconducting gap known to exist in multigap superconductors-for different possible symmetries of the superconducting order parameter. Specifically, we identify the small regions of parameter space where the Leggett mode lies below the two-particle continuum, and hence should be visible as a sharp resonance peak. We discuss the possible utility of the Leggett mode in distinguishing different momentum dependencies of the superconducting gap. We argue that the observation of a sharp Leggett mode would be consistent with the presence of strong electron-electron correlations in ironbased superconductors. We also emphasize the importance of the orbital character of the Leggett mode, which can result in an experimental observation of the mode in channels other than A 1g .

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2003 Nobel Prize in Physics for Theoretical Work on Superfluid ³He

Leggett

2004

ChemPhysChem

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The element helium comes in two (stable) forms, 4He and 3He; at low temperatures and pressures both form liquids rather than solids. The liquid phase of the common isotope, 4He, was realized nearly a century ago, and since 1938 has been known to show, at temperatures below about 2K, the property of superfluidity--the ability to flow through the narrowest capillaries without apparent friction. The light isotope, 3He, is believed to be of quite a different nature; however, because of its similarity to the electrons in metals, which at low temperatures sometimes form "Cooper pairs" and thereby become superconducting, theorists in the 1960s and early 1970s had speculated that something similar might happen in liquid 3He, which would then also show superfluidity though for reasons rather different than 4He. In 1972 nuclear magnetic resonance (NMR) experiments at Cornell University revealed the existence, below 3 millidegrees, if two new phases, one of which displayed extraordinary NMR properties. Anthony Leggett is one of the theorists who succeeded in fitting the experimental properties into the "Cooper-pairing" scenario; in particular, he explained the NMR behavior and predicted further novel NMR phenomena which were subsequently found.

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Evidence for a two-band behavior of MgB2 from point-contact and tunneling spectroscopy

Cited by 74 publications

References 25 publications

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

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

Leggett mode in a strong-coupling model of iron arsenide superconductors

2003 Nobel Prize in Physics for Theoretical Work on Superfluid ³He

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Evidence for a two-band behavior of MgB2 from point-contact and tunneling spectroscopy

Cited by 74 publications

References 25 publications

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

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

Leggett mode in a strong-coupling model of iron arsenide superconductors

2003 Nobel Prize in Physics for Theoretical Work on Superfluid 3He

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Product

Resources

About

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

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

2003 Nobel Prize in Physics for Theoretical Work on Superfluid ³He