Effect of dimensionality on the vortex dynamics in a type-II superconductor Article Swipe
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· 2019
· Open Access
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· DOI: https://doi.org/10.1103/physrevb.100.174501
· OA: W2987109028
We explore the effects of sample dimensionality on vortex pinning in a\ntype-II, low-$T_C$, s-wave superconductor, NbN, in the presence of a\nperpendicular magnetic field, $H$. We find significant differences in the phase\ndiagrams in the magnetic field--temperature plane between 3-dimensional (3D)\nand 2-dimensional (2D) NbN films. The differences are most striking close to\nthe normal-superconductor phase transition. We establish that these variances\nhave their origin in the differing pinning properties in two different\ndimensions. We obtain the pinning strength quantitatively in both the\ndimensions from two independent transport measurements performed in two\ndifferent regimes of vortex-motion -- (i) thermally assisted flux-flow (TAFF)\nregime and (ii) flux flow (FF) regime. Both the measurements consistently show\nthat both the pinning potential and the zero-field free-energy barrier to\ndepinning in the 3D superconductor are at least an order of magnitude stronger\nthan that in the 2D superconductor. Further, we probed the dynamics of pinning\nin both 2D and 3D superconductor through voltage fluctuation spectroscopy. We\nfind that the mechanism of vortex pinning-depinning is qualitatively similar\nfor the 3D and 2D superconductors. The voltage-fluctuations arising from\nvortex-motion are found to be correlated only in the 2D superconductor. We\nestablish this to be due to the presence of long-range phase fluctuations near\nthe Berezinskii-Kosterlitz-Thouless (BKT) type superconducting transition in\n2-dimensional superconductors.\n