Equilibrium properties of superconducting niobium at high magnetic fields

A possible existence of a filamentary state in type-II superconductors

V. Kozhevnikov, A. M. Valente-Feliciano, P. J. Curran, A Suter, Albert Yung-hsu Liu, Goezt M Richter, E. Morenzoni, S. J. Bending, C. Van Haesendonck

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Abstract

The standard interpretation of the phase diagram of type-II superconductors was developed in the 1960s and has since been considered a well-established part of classical superconductivity. However, upon closer examination a number of fundamental issues arises that leads one to question this standard picture. To address these issues we studied equilibrium properties of niobium samples near and above the upper critical field Hc2 in parallel and perpendicular magnetic fields. The samples investigated were very high quality films and single-crystal disks with the Ginzburg-Landau parameters 0.8 and 1.3, respectively. A range of complementary measurements has been performed, which include dc magnetometry, electrical transport, muon spin rotation spectroscopy, and scanning Hall-probe microscopy. Contrary to the standard scenario, we observed that a superconducting phase is present in the sample bulk above Hc2 and the field Hc3 is the same in both parallel and perpendicular fields. Our findings suggest that above Hc2 the superconducting phase forms filaments parallel to the field regardless of the field orientation. Near Hc2 the filaments preserve the hexagonal structure of the preceding vortex lattice of the mixed state, and the filament density continuously falls to zero at Hc3. Our paper has important implications for the correct interpretation of the properties of type-II superconductors and can be essential for practical applications of these materials.

Original languageEnglish
Article number174509
JournalPhysical Review B
Volume95
Issue number17
DOIs
Publication statusPublished - 17 May 2017

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Niobium
niobium
Superconducting materials
filaments
Magnetic fields
magnetic fields
muon spin rotation
Superconductivity
Phase diagrams
magnetic measurement
Microscopic examination
Vortex flow
superconductivity
examination
phase diagrams
Single crystals
Spectroscopy
vortices
microscopy
Scanning

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Kozhevnikov, V., Valente-Feliciano, A. M., Curran, P. J., Suter, A., Liu, A. Y., Richter, G. M., ... Van Haesendonck, C. (2017). Equilibrium properties of superconducting niobium at high magnetic fields: A possible existence of a filamentary state in type-II superconductors. Physical Review B, 95(17), [174509]. https://doi.org/10.1103/PhysRevB.95.174509

Equilibrium properties of superconducting niobium at high magnetic fields : A possible existence of a filamentary state in type-II superconductors. / Kozhevnikov, V.; Valente-Feliciano, A. M.; Curran, P. J.; Suter, A; Liu, Albert Yung-hsu; Richter, Goezt M; Morenzoni, E.; Bending, S. J.; Van Haesendonck, C.

In: Physical Review B, Vol. 95, No. 17, 174509, 17.05.2017.

Research output: Contribution to journalArticle

Kozhevnikov, V, Valente-Feliciano, AM, Curran, PJ, Suter, A, Liu, AY, Richter, GM, Morenzoni, E, Bending, SJ & Van Haesendonck, C 2017, 'Equilibrium properties of superconducting niobium at high magnetic fields: A possible existence of a filamentary state in type-II superconductors', Physical Review B, vol. 95, no. 17, 174509. https://doi.org/10.1103/PhysRevB.95.174509
Kozhevnikov, V. ; Valente-Feliciano, A. M. ; Curran, P. J. ; Suter, A ; Liu, Albert Yung-hsu ; Richter, Goezt M ; Morenzoni, E. ; Bending, S. J. ; Van Haesendonck, C. / Equilibrium properties of superconducting niobium at high magnetic fields : A possible existence of a filamentary state in type-II superconductors. In: Physical Review B. 2017 ; Vol. 95, No. 17.
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