Microwave Surface Impedance Measurements of LiFeAs Single Crystals

Imai, Yoshio; Takahashi, Hideyuki; Kitagawa, Kentaro; Matsubayashi, Kazuyuki; Nakai, N.; Nagai, Yuki; Uwatoko, Yoshiya; Machida, Masahiko; Maeda, Akiko

doi:10.1143/jpsj.80.013704

Cited by 42 publications

(42 citation statements)

References 39 publications

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“…Therefore, we compare our results with the data by the number of scientific groups in the Table 1. Angle-resolved photoemission spectroscopy (ARPES) on LiFeAs single crystals [3,27,28], specific heat [27,46], London penetration depth [28,47,48], and microwave surface impedance [49] yield similar results for the number and values of superconducting gaps (see Table 1). The distinction in the BCS-ratio values should be taken into account.…”

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confidence: 89%

“…The distinction in the BCS-ratio values should be taken into account. On calculating 2∆/k B T C the T onset C in [3,27,28,46,47,49,50] and T bulk C in [48] have been used, which are average values that may be higher or lower than the T local C in the point of gap defining due to a samples inhomogeneity if any. By contrast, operating with the local T C , one can calculate the BCS-ratio value more accurately.…”

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confidence: 99%

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Investigation of LiFeAs by means of “break-junction” technique

et al. 2012

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In our tunneling investigation using Andreev superconductor -normal metal -superconductor contacts on LiFeAs single crystals we observed two reproducible independent subharmonic gap structures at dynamic conductance characteristics. From these results, we can derive the energy of the large superconducting gap ∆L = (2.5 ÷ 3.4) meV and the small gap ∆S = (0.9 ÷ 1) meV at T = 4.2 K for the T local C ≈ (10.5 ÷ 14) K (the contact area critical temperature which deviation causes the variation of ∆L). The BCS-ratio is found to be 2∆L/kBTC = (4.6 ÷ 5.6), whereas 2∆S/kBTC ≪ 3.52 results from induced superconductivity in the bands with the small gap.The new class of superconducting rare-earth oxypnictides [1] is still not completely understood and therefore requires further investigation. The layered LiFeAs (111-system) [2] is one of the few stoichiometric Febased pnictides which shows neither magnetic nor structural transition but becomes superconducting at 18 K [3,4]. Band-structure calculations [5,6,7] show the Fermi surfaces for 111-system to be comprised of quasitwo-dimensional (2D) hole cylinders centered at the Γ-point and electron ones at the M-point of the first Brillouin zone that can be considered as two effective bands (so called minimal two-band model) [8,9]. The total density of states at the Fermi level is formed mainly by Fe 3d-states [10,11,12,13,14]. As was shown in [15], the superconducting transition temperatures T C for different types of iron-based superconductors correlate with the total density of states at the Fermi level. This fact and the strong Fe isotope effect, which was reported by [16] supports the phonon-mediated coupling importance [17] in these compounds [15,18]. The electron-phonon coupling is enhanced by an extended van Hove singularity [19] which was shown for iron pnictides and, in particular, for LiFeAs [20]. In this work, we present an investigation of the superconducting properties of LiFeAs single crystals by means of Andreev spectroscopy of superconductor -normal metal -superconductor (SNS) contacts, and the corresponding superconducting gaps.The LiFeAs single crystals were obtained by self-flux method. The synthesis and investigation of the composition and properties are detailed in [21]. A mixture of small lumps of the Li metal and powders of Fe and As in a molar ratio of Li : Fe : As = 3 : 2 : 3 was 1) e-mail: kuzmichev@mig.phys.msu.ru placed into an alumina crucible. All work on the reactive mixture preparation was carried out in a dry box under argon atmosphere. The crucible was inserted into a niobium container, which was welded in argon at 1.5 atm. The sealed Nb container was enclosed in a quartz ampoule. The sample was heated up to 1363 K, kept at this temperature and slowly cooled down to 873 K. At this temperature ampoule was extracted from the furnace and cooled in open air. The LiFeAs single crystals in the form of thin plates with lateral dimensions of (12 ± 6) × (12 ± 6) × (0.1 ± 0.05) mm 3 were separated from flux mechanically. According to the XRD, EDX, ICP MS, a...

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Investigation of LiFeAs by means of “break-junction” technique

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“…On the other hand, it seems commonly accepted that the superconducting gap is nodeless as confirmed by a large body of experimental results like NMR [130], specific heat [131], ARPES [132] and penetration depth measurements [133,134]. In order to explore these different ordering tendencies, the FRG formalism allows to employ a combined approach of density functional theory (DFT) and FRG which connects an ab initio description with the unbiased analysis of functional RG.…”

Section: P-based Compoundsmentioning

confidence: 99%

Functional renormalization group for multi-orbital Fermi surface instabilities

Platt

Hanke

Thomale

2013

Advances in Physics

196

253

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Technological progress in material synthesis, as well as artificial realization of condensed matter scenarios via ultra-cold atomic gases in optical lattices or epitaxial growth of thin films, is opening the gate to investigate a plethora of unprecedented strongly correlated electron systems. In a large subclass thereof, a metallic state of layered electrons undergoes an ordering transition below some temperature into unconventional states of matter driven by electronic correlations, such as magnetism, superconductivity, or other Fermi surface instabilities. While this type of phenomena has been a well-established direction of research in condensed matter for decades, the variety of today's accessible scenarios pose fundamental new challenges to describe them. A core complication is the multi-orbital nature of the low-energy electronic structure of these systems, such as the multi-d orbital nature of electrons in iron pnictides and transition-metal oxides in general, but also electronic states of matter on lattices with multiple sites per unit cell such as the honeycomb or kagome lattice. In this review, we propagate the functional renormalization group (FRG) as a suited approach to investigate multi-orbital Fermi surface instabilities. The primary goal of the review is to describe the FRG in explicit detail and render it accessible to everyone both at a technical and intuitive level. Summarizing recent progress in the field of multi-orbital Fermi surface instabilities, we illustrate how the unbiased fashion by which the FRG treats all kinds of ordering tendencies guarantees an adequate description of electronic phase diagrams and often allows to obtain parameter trends of sufficient accuracy to make qualitative predictions for experiments. This review includes detailed and illustrative illustrations of magnetism and, in particular, superconductivity for the iron pnictides from the viewpoint of FRG. Furthermore, it discusses candidate scenarios for topological bulk singlet superconductivity and exotic particle-hole condensates on hexagonal lattices such as sodium-doped cobaltates, graphene doped to van Hove filling, and the kagome Hubbard model. In total, the FRG promises to be one of the most versatile and revealing numerical approaches to address unconventional Fermi surface instabilities in future fields of condensed matter research.

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“…6,7) On the other hand, mechanisms based on the orbital fluctuation favor the s ++ symmetry with the same sign of the order parameter for both hole bands and electron bands. 8,9) The absence of the coherence enhancement in the temperature dependence of the spin relaxation rate 2,10) and microwave conductivity [11][12][13][14] in many materials suggests the sign changing s ± wave. More detailed study of the coherence factor by STM in FeSe 1−x Te x (the so-called 11 material) 15) also suggests the s ± wave definitely.…”

Section: Introductionmentioning

confidence: 99%

Effect of Co Impurities on Superconductivity of FeSe_0.4Te_0.6Single Crystals

Nabeshima¹,

Kobayashi²,

Imai³

et al. 2012

Jpn. J. Appl. Phys.

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The effect of Co doping on supercoductivity of FeSe 0.4 Te 0.6 single crystals is investigated. The superconducting transition temperature decreases linearly for Co doping with the rate -0.75 K/(Co %). On the other hand, the increase of the residual resistivity is less than 50 µΩcm for 4 % Co doping. These data are consistent with the interband scattering mechanism of superconductivity with the sign change (s ± symmetry).

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Microwave Surface Impedance Measurements of LiFeAs Single Crystals

Cited by 42 publications

References 39 publications

Investigation of LiFeAs by means of “break-junction” technique

Investigation of LiFeAs by means of “break-junction” technique

Functional renormalization group for multi-orbital Fermi surface instabilities

Effect of Co Impurities on Superconductivity of FeSe_0.4Te_0.6Single Crystals

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Microwave Surface Impedance Measurements of LiFeAs Single Crystals

Cited by 42 publications

References 39 publications

Investigation of LiFeAs by means of “break-junction” technique

Investigation of LiFeAs by means of “break-junction” technique

Functional renormalization group for multi-orbital Fermi surface instabilities

Effect of Co Impurities on Superconductivity of FeSe0.4Te0.6Single Crystals

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Effect of Co Impurities on Superconductivity of FeSe_0.4Te_0.6Single Crystals