Influence of point defects on the vortex state of disordered superconductors

Pradhan, A. K.; Muralidhar, M.; Feng, Yang; Murakami, Masato; Nakao, Kōichi; Koshizuka, N.

doi:10.1103/physrevb.64.172505

Cited by 37 publications

(44 citation statements)

References 21 publications

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“…where R(α) = (cos 2 α + ǫ sin decreases from ≃ 2 − 3 to ≃ 1 as T decreases [46,47,48,49,50,51,52,53,54,55,56]. This behavior was explained by the two-gap theory in the clean limit [57,58,83,84].…”

Section: Anisotropy Of Hc1 and Hc2mentioning

confidence: 98%

Limits of the upper critical field in dirty two-gap superconductors

Gurevich

2007

Physica C: Superconductivity

175

189

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An overview of the theory of the upper critical field in dirty two-gap superconductors, with a particular emphasis on MgB2 is given. We focus here on the maximum Hc2 which may be achieved by increasing intraband scattering, and on the limitations imposed by weak interband scattering and paramagnetic effects. In particular, we discuss recent experiments which have recently demonstrated ten-fold increase of Hc2 in dirty carbon-doped films as compared to single crystals, so that the Hc2(0) parallel to the ab planes may approach the BCS paramagnetic limit, Hp[T ] = 1.84Tc[K] ≃ 60 − 70T . New effects produced by weak interband scattering in the two-gap Ginzburg-Landau equations and Hc2(T ) in ultrathin MgB2 films are addressed.

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Section: Anisotropy Of Hc1 and Hc2mentioning

confidence: 98%

Limits of the upper critical field in dirty two-gap superconductors

Gurevich

2007

Physica C: Superconductivity

175

189

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“…However, fluctuations are not expected to play any significant role in MgB 2 as confirmed by specific heat measurments: the width ∆C does not increase significantly with magnetic field and the upper critical field occurs near the onset of finite resistance at H R=0 . A non correct criterion for the H c2 determination partly explains the discrepancy in the values deduced from transport measurments 22,23 . Next, we discuss the angular dependence of the critical field.…”

Section: H − T Phase Diagrammentioning

confidence: 99%

Anisotropy of the upper critical field and critical current in single crystalMgB2

et al. 2002

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We report on specific heat, high magnetic field transport and ac−susceptibility measurments on magnesium diboride single crystals. The upper critical field Hc2 for magnetic fields perpendicular and parallel to the Mg and B planes is presented for the first time in the entire temperature range. A very different temperature dependence has been observed in the two directions which yields to a temperature dependent anisotropy with Γ ∼ 5 at low temperatures and about 2 near Tc. A peak effect is observed in the susceptibility measurments for µ0H ∼2 T parallel to the c−axis and the critical current density presents a sharp maximum for H parallel to the ab−plane.

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“…Different models are proposed to explain the particular properties of MgB 2 [4,5]. Their correctness has to be checked by experiments, but only a few results are available on single crystals [6,7,8,9,10,11,12].We report in this Letter on magnetization measurements on single crystalline MgB 2 in magnetic fields applied parallel and perpendicular to the uniaxial crystallographic (≡ c) axis. A detailed evaluation allows us to obtain the temperature dependence of the most important reversible mixed state parameters, such as the critical magnetic fields, the characteristic lengths, the Ginzburg-Landau (GL) parameter and the anisotropy.…”

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Mixed-state properties of superconductingMgB2single crystals

et al. 2002

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We report on measurements of the magnetic moment in superconducting MgB2 single crystals. We find µ0H c c2 (0) = 3.2 T, µ0H ab c2 (0) = 14.5 T, γ = 4.6, µ0Hc(0) = 0.28 T, and κ(Tc) = 4.7. The standard Ginzburg-Landau and London model relations lead to a consistent data set and indicate that MgB2 is a clean limit superconductor of intermediate coupling strength with very pronounced anisotropy effects.PACS numbers: 74.25. Ha, 74.60.Ec, 74.70.Ad The recent discovery of superconductivity in MgB 2 [1] has attracted a lot of attention. Especially the rather high transition temperature of nearly 40 K in such a simple compound is of interest for applications, but also for an analysis of the physical mechanism leading to superconductivity. Several experiments indicate a phonon mediated s -wave BCS mechanism [2,3]. Different models are proposed to explain the particular properties of MgB 2 [4,5]. Their correctness has to be checked by experiments, but only a few results are available on single crystals [6,7,8,9,10,11,12].We report in this Letter on magnetization measurements on single crystalline MgB 2 in magnetic fields applied parallel and perpendicular to the uniaxial crystallographic (≡ c) axis. A detailed evaluation allows us to obtain the temperature dependence of the most important reversible mixed state parameters, such as the critical magnetic fields, the characteristic lengths, the Ginzburg-Landau (GL) parameter and the anisotropy. We will show that MgB 2 is a clean limit superconductor of intermediate coupling strength with very pronounced anisotropy effects.Several single crystals of MgB 2 were grown using high pressure cubic anvils. Details of the process will be published elsewhere [13]. Two crystals (sample A:3 ) were investigated by magnetic methods. The transition temperature (T c ) of each sample was obtained from the ac -susceptibility measured in a 1 T quantum interference device (SQUID) magnetometer. Sample A shows an onset of T c at 38 K and a rather broad transition of about 1 K. A linear fit of H c c2 vs. T near T c indicates a "bulk transition temperature" of 37.5 K (see inset of fig. 1a). In sample B we find T c = 38.3 K, ∆ T c = 0.3 K and a "bulk T c " of 38.2 K. A simple analysis [14] of the slope of the magnetic moment after reversing the applied field demonstrates that the size of the domain, in which the supercurrents flow without impedance, is identical to the sample size. Furthermore, a comparison of the calculated and the measured magnetization in the Meissner regime indicates a superconducting volume fraction of about 100 %. The further evaluation of the mixed state parameters did not show significant differences between these two crystals.The measurements of the magnetic moment were carried out in the 1 T and in an 8 T (SHE) SQUID magnetometer (for details, cf. [15]). Fig. 1a shows the upper critical field of MgB 2 for applied fields H a c (H c c2 ) and H a ab (H ab c2 ). H c2 (T ) is determined either from the onset of the superconducting signal in the m(T ) curve ("T c (H a )") or ...

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Influence of point defects on the vortex state of disordered superconductors

Cited by 37 publications

References 21 publications

Limits of the upper critical field in dirty two-gap superconductors

Limits of the upper critical field in dirty two-gap superconductors

Anisotropy of the upper critical field and critical current in single crystalMgB2

Mixed-state properties of superconductingMgB2single crystals

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