Microscopic theory of the lower critical field in superconducting thin-film strips
Abstract
The lower critical field Bc1 of a narrow superconducting thin-film strip sets the thermodynamic scale for vortex-free operation in a perpendicular magnetic field. The standard Pearl--London estimate requires a phenomenological vortex-core cutoff, because the London theory does not resolve the core. We formulate a microscopic theory for a dirty strip by solving the two-dimensional Usadel equations in the film plane, with the applied field included directly in the gauge-invariant momentum. Self-consistent vortex and Meissner solutions are computed at fixed field, and Bc1 is obtained from their Gibbs-energy difference. The calculation resolves the vortex core and its finite-width deformation without introducing a cutoff. The resulting vortex self-energy is larger than the naive Pearl--London estimate and cannot, in general, be represented by a London logarithm with a single width-independent cutoff. The formulation applies at any T<Tc and provides a microscopic basis for predicting Bc1 in superconducting nanostrips and related thin-film devices.
Versions
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BibTeX
@misc{kubo2026microscopic,
title = {{Microscopic theory of the lower critical field in superconducting thin-film strips}},
author = {Takayuki Kubo},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2607.05890},
eprint = {2607.05890},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.05890},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Microscopic theory of the lower critical field in superconducting thin-film strips
AU - Takayuki Kubo
PY - 2026
DA - 2026/10/22
PB - arXiv
DO - 10.48550/arxiv.2607.05890
UR - https://arxiv.org/abs/2607.05890
AB - The lower critical field B_c1 of a narrow superconducting thin-film strip sets the thermodynamic scale for vortex-free operation in a perpendicular magnetic field. The standard Pearl--London estimate requires a phenomenological vortex-core cutoff, because the London theory does not resolve the core. We formulate a microscopic theory for a dirty strip by solving the two-dimensional Usadel equations in the film plane, with the applied field included directly in the gauge-invariant momentum. Self-consistent vortex and Meissner solutions are computed at fixed field, and B_c1 is obtained from their Gibbs-energy difference. The calculation resolves the vortex core and its finite-width deformation without introducing a cutoff. The resulting vortex self-energy is larger than the naive Pearl--London estimate and cannot, in general, be represented by a London logarithm with a single width-independent cutoff. The formulation applies at any T<T_c and provides a microscopic basis for predicting B_c1 in superconducting nanostrips and related thin-film devices.
ER -