Vortex Imaging in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>π</mml:mi></mml:math>Band of Magnesium Diboride

Eskildsen, M. R.; Kugler, Martin; Tanaka, Shukichi; Jun, J.; Казаков, С. М.; Karpiński, J.; Fischer, Ø.

doi:10.1103/physrevlett.89.187003

Cited by 285 publications

(345 citation statements)

References 25 publications

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“…In spite of a probably common vortex pinning mechanism in both bulk MgB 2 and Nb 3 Sn, vortex pinning in MgB 2 is apparently weaker (lower B max and B irr ) than that in Nb 3 Sn. The probable reason for that are larger grains, clean and narrow grain boundaries, and quite a large coherence length [30] in MgB 2 . The J c (B) variation of nanoparticle doped MgB 2 sample (Fig.…”

Section: Resultsmentioning

confidence: 99%

Correlated vortex pinning in Si-nanoparticle doped MgB2

Kušević

Babić

Husnjak

et al. 2004

Solid State Communications

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The magnetoresistivity and critical current density of well characterized Si-nanoparticle doped and undoped Cu-sheathed MgB2 tapes have been measured at temperatures T ≥ 28 K in magnetic fields B ≤ 0.9 T. The irreversibility line Birr(T ) for doped tape shows a stepwise variation with a kink around 0.3 T. Such Birr(T ) variation is typical for high-temperature superconductors with columnar defects (a kink occurs near the matching field B φ ) and is very different from a smooth Birr(T ) variation in undoped MgB2 samples. The microstructure studies of nanoparticle doped MgB2 samples show uniformly dispersed nanoprecipitates, which probably act as a correlated disorder. The observed difference between the field variations of the critical current density and pinning force density of the doped and undoped tape supports the above findings.

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Section: Resultsmentioning

confidence: 99%

Correlated vortex pinning in Si-nanoparticle doped MgB2

Kušević

Babić

Husnjak

et al. 2004

Solid State Communications

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“…The scanning tunneling spectroscopy (STS) images of vortices parallel to the c axis [13] have been successfully explained by theory [4]. Importantly, vortex imaging is demanding experimentally and probes mainly the properties of the π band.…”

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confidence: 93%

“…It is in principle possible to obtain the scattering rates from the temperature dependence of the resistivity [7,8], but this method is subject to large uncertainty if the sample is not 100% dense [9], which is often the case with MgB 2 . In this work we demonstrate that the diffusivity ratio can be directly evaluated from point-contact Andreev reflection (PCAR) spectroscopy in magnetic field.Point-contact [10,11,12] and tunnelling spectroscopies [13,14], have been used to study the properties of MgB 2 in applied magnetic field. The scanning tunneling spectroscopy (STS) images of vortices parallel to the c axis [13] have been successfully explained by theory [4].…”

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Electron diffusivities inMgB2from point contact spectroscopy

et al. 2005

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We demonstrate that the variation of the Andreev reflection with applied magnetic field provides a direct means of comparing the properties of MgB 2 with the theory for a dirty two-band superconductor, and we find good agreement between the two. The ratio of electron diffusivities in the σ and π bands can be inferred from this experiment. We find that the field dependence of the density of states at the Fermi level in the π band is independent of the field direction, and that the anisotropic upper critical field is determined by the anisotropic diffusivity in the σ band. ) will change the resulting macroscopic superconducting properties, and therefore independent determination of this ratio has emerged as a key prerequisite to understand and control the properties of MgB 2 . Due to the crystalline anisotropy, the diffusivities along the c axis ( ). It is in principle possible to obtain the scattering rates from the temperature dependence of the resistivity [7,8], but this method is subject to large uncertainty if the sample is not 100% dense [9], which is often the case with MgB 2 . In this work we demonstrate that the diffusivity ratio can be directly evaluated from point-contact Andreev reflection (PCAR) spectroscopy in magnetic field.Point-contact [10,11,12] and tunnelling spectroscopies [13,14], have been used to study the properties of MgB 2 in applied magnetic field. The scanning tunneling spectroscopy (STS) images of vortices parallel to the c axis [13] have been successfully explained by theory [4]. Importantly, vortex imaging is demanding experimentally and probes mainly the properties of the π band. It is possible to use the STS method to probe the in-plane vortices in sufficiently thick single crystals [14], but certainly not in thin films. The effect of vortices on the point-contact measurements has not been considered.In our previous work [15] we have demonstrated that as the field is increased, the transition to the normal state occurs simultaneously in the two superconducting sub-systems, i.e., the σ and π bands are characterised by a unique H c2 . Later we have studied the evolution of the PCAR spectra with magnetic field in niobium [16]; we showed that the mechanism behind the field variation of the Andreev reflection in Type-II superconductor is the presence of normal vortex cores, which leads to effective broadening of the spectra and increasing the zero-energy density of states (DOS), N 0 (corresponding

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“…The effect of the two-gap structure on vortex dynamics is presently under intense investigation. Although STM [9] and specific heat measurements [10] indicate a rapid suppression of the π gap with increasing magnetic field its effect on magneto-transport properties remains controversial. In particular, a pronounced broadening of the resistive transitions in magnetic fields applied along the c axis has been observed.…”

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confidence: 99%

Surface contribution to the superconducting properties ofMgB2single crystals

et al. 2003

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We demonstrate direct evidence of possible surface superconductivity on small, well-shaped MgB2 single crystals. Transport measurements in the range H < 1.6H c c2 , where H c c2 is the bulk upper critical field for the c axis, show non-Ohmic and strongly angular dependent resistivity. Studies of the alignment of H with selected crystal surfaces, transport and specific heat measurements on the same crystal, and a physical sculpturing of the crystal surfaces using a focused ion beam all support the conclusion. Similar, albeit less pronounced results are obtained for fields in the basal plane.

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Vortex Imaging in theπBand of Magnesium Diboride

Cited by 285 publications

References 25 publications

Correlated vortex pinning in Si-nanoparticle doped MgB2

Correlated vortex pinning in Si-nanoparticle doped MgB2

Electron diffusivities inMgB2from point contact spectroscopy

Surface contribution to the superconducting properties ofMgB2single crystals

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