Exponential Temperature Dependence of the Penetration Depth in Single Crystal<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>MgB</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Manzano, F; Carrington, A.; Hussey, N. E.; Lee, S; Yamamoto, Atsushi; Tajima, S.

doi:10.1103/physrevlett.88.047002

Cited by 157 publications

(141 citation statements)

References 21 publications

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“…We find that the temperature dependence of ∆λ c is similar to ∆λ a , but a factor ∼ 2 larger. This is consistent with the behavior reported previously [17], although in that study the crystals used were not of sufficiently uniform thickness to accurately determine λ c .…”

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confidence: 81%

Temperature-Dependent Anisotropy of the Penetration Depth and Coherence Length ofMgB2

et al. 2005

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We report measurements of the temperature dependent anisotropies (γ λ and γ ξ ) of both the London penetration depth λ and the upper critical field of MgB2. Data for γ λ = λc/λa was obtained from measurements of λa and λc on a single crystal sample using a tunnel diode oscillator technique. γ ξ = H c c2 /H ⊥c c2 was deduced from field dependent specific heat measurements on the same sample. γ λ and γ ξ have opposite temperature dependencies, but close to Tc tend to a common value (γ λ ≃ γ ξ = 1.75 ± 0.05). These results are in good agreement with theories accounting for the two gap nature of MgB2.The existence of two superconducting gaps in MgB 2 [1] leads to an unusually strong temperature dependence in the anisotropy of the upper critical field, Refs. 2,3,4,5). The maximum value of γ ξ ≃ 6 is found at the lowest temperatures where it is dominated by the anisotropy in the quasi two dimensional σ bands. At higher temperatures, γ ξ is substantially reduced due to the increasing contribution of the more isotropic π band [5]. The anisotropy of the penetration depth, γ λ = λ c /λ a , is predicted to have a markedly different temperature dependence to that of H c2 [4,6]. At zero temperature, in the clean local limit, the anisotropy in the penetration depth is determined only by the anisotropy in the Fermi velocity v F and not by the anisotropy in the gap [7]. Band structure calculations [8] show that the average v F is approximately isotropic suggesting that λ is similarly isotropic at low temperature [4]. As temperature is increased it has been predicted [4,6] that γ λ increases markedly because of the more rapid reduction of the superfluid density on the π sheets (where the gap is smaller) than on the σ sheets.There have been several experimental measurements of the temperature dependence of γ ξ . Although there were some disagreements in early measurements, the most recent data [2, 3, 9] agree well with the theoretical predictions [4,5]. Significantly less experimental data has been reported on γ λ . Measurements of the distortion of the vortex lattice by neutron scattering [10] and scanning tunneling spectroscopy [11] suggest that at low temperature the anisotropy is small, γ λ = 1.2 ± 0.1. γ λ has also been estimated from the anisotropy of H c1 (γ Hc1 = H c c1 /H ⊥c c1 ). There has been some disagreement between different studies (see Ref. 12) but recent data [12] suggest that at low T , γ Hc1 ≃ 1 and there is an upward trend in γ Hc1 near T c . However, γ Hc1 may not be simply related to γ λ in MgB 2 because of two gap effects. In this paper, we present direct measurements of the temperature dependencies of λ a and λ c in single crystal samples of MgB 2 in the Meissner state, using a sensitive radio frequency technique. Our data show that γ λ increases as T → T c , in agreement with theoretical predictions. Measurements of H c2 anisotropy in the same crystals show that the values of γ λ and γ ξ converge as T → T c .Single crystals of MgB 2 were grown using a high pressure technique described elsewhere [13]. Som...

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Temperature-Dependent Anisotropy of the Penetration Depth and Coherence Length ofMgB2

et al. 2005

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“…Obviously, the occurrence of the kink in H c1 (T ) can not be explained by the model with an s-wave or d-wave single gap. On the other hand, this kinky structure in H c1 (T ) resembles that of the related penetration depth of the two-band superconductor MgB 2 [28], in which a positive curvature was observed and explained by the multi-band theory [29]. In addition, recent ARPES measurement resolved a twogap nature in a similar Ba 0.6 K 0.4 Fe 2 As 2 crystal [30,31].…”

Section: Shown Inmentioning

confidence: 95%

Evidence for Two Energy Gaps in SuperconductingBa0.6K0.4Fe2As2Single Crystals and the Breakdown of the Uemura Plot

et al. 2008

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We report a detailed investigation on the lower critical field Hc1 of the superconducting Ba0.6K0.4Fe2As2 (FeAs-122) single crystals. A pronounced kink is observed on the Hc1(T ) curve, which is attributed to the existence of two superconducting gaps. By fitting the data Hc1(T ) to the two-gap BCS model in full temperature region, a small gap of ∆a(0) = 2.0 ± 0.3 meV and a large gap of ∆ b (0) = 8.9 ± 0.4 meV are obtained. The in-plane penetration depth λ ab (0) is estimated to be 105 nm corresponding to a rather large superfluid density, which points to the breakdown of the Uemura plot in FeAs-122 superconductors.

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“…[160,142] 5. Absolute value of the penetration depth Resonator perturbation methods, whether low or high frequency, provide extremely precise measurements of changes, Δλ, in the penetration depth as a function of an external parameter; typically temperature or magnetic field.…”

Section: Penetration Depth In Anisotropic Samplesmentioning

confidence: 99%

Magnetic penetration depth in unconventional superconductors

Prozorov

Giannetta

2006

Supercond. Sci. Technol.

417

438

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Abstract. This topical review summarizes various features of magnetic penetration depth in unconventional superconductors. Precise measurements of the penetration depth as a function of temperature, magnetic field and crystal orientation can provide detailed information about the pairing state. Examples are given of unconventional pairing in hole-and electron-doped cuprates, organic and heavy fermion superconductors. The ability to apply an external magnetic field adds a new dimension to penetration depth measurements. We discuss how field dependent measurements can be used to study surface Andreev bound states, nonlinear Meissner effects, magnetic impurities, magnetic ordering, proximity effects and vortex motion. We also discuss how penetration depth measurements as a function of orientation can be used to explore superconductors with more than one gap and with anisotropic gaps. Details relevant to the analysis of penetration depth data in anisotropic samples are also discussed.Keywords: penetration depth, unconventional superconductivity, pairing symmetry IntroductionThe early suggestion that high temperature superconductors might exhibit unconventional, d-wave pairing, [24,11,154,8] has lead to a wide variety of new experimental probes with sensitivity sufficient to test this hypothesis. The pioneering work of Hardy and coworkers demonstrated that high resolution measurements of the London penetration depth could detect the presence of nodal quasiparticles characteristic of a d-wave pairing state [87]. Since that time, a large number of new superconductors have been discovered, many of which exhibit nontrivial departures from BCS behavior. As we show in this review, penetration depth measurements can be used to examine not only nodal quasiparticles but two-gap superconductivity, anisotropy of the energy gap, Andreev surface states, nonlinear Meissner effect, interplane transport, proximity coupled diamagnetism, vortex matter and the coexistence of magnetism and superconductivity, to name several problems of current interest.

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Exponential Temperature Dependence of the Penetration Depth in Single CrystalMgB2

Cited by 157 publications

References 21 publications

Temperature-Dependent Anisotropy of the Penetration Depth and Coherence Length ofMgB2

Temperature-Dependent Anisotropy of the Penetration Depth and Coherence Length ofMgB2

Evidence for Two Energy Gaps in SuperconductingBa0.6K0.4Fe2As2Single Crystals and the Breakdown of the Uemura Plot

Magnetic penetration depth in unconventional superconductors

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