Spontaneous symmetry breaking in vortex systems with two repulsive lengthscales.
Scanning Hall probe microscopy (SHPM) has been used to study vortex structures in thin epitaxial films of the superconductor MgB2. Unusual vortex patterns observed in MgB2 single crystals have previously been attributed to a competition between short-range repulsive and long-range attractive vortex-vortex interactions in this two band superconductor; the type 1.5 superconductivity scenario. Our films have much higher levels of disorder than bulk single crystals and therefore both superconducting condensates are expected to be pushed deep into the type 2 regime with purely repulsive vortex interactions. We observe broken symmetry vortex patterns at low fields in all samples after field-cooling from above Tc. These are consistent with those seen in systems with competing repulsions on disparate length scales, and remarkably similar structures are reproduced in dirty two band Ginzburg-Landau calculations, where the simulation parameters have been defined by experimental observations. This suggests that in our dirty MgB2 films, the symmetry of the vortex structures is broken by the presence of vortex repulsions with two different lengthscales, originating from the two distinct superconducting condensates. This represents an entirely new mechanism for spontaneous symmetry breaking in systems of superconducting vortices, with important implications for pinning phenomena and high current density applications.
University of Bath, Department of Physics, Bath, BA2 7AY, UK.
P J
PJ
Curran
University of Bath, Department of Physics, Bath, BA2 7AY, UK.|University of Zagazig, Department of Physics, Ash Sharqiyah, Egypt.
W M
WM
Desoky
Universiteit Antwerpen, Departement Fysica, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium.|Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, 60455-900 Fortaleza, Ceará, Brazil.
M V
MV
Milosević
Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, 60455-900 Fortaleza, Ceará, Brazil.
A
A
Chaves
Francis Bitter Magnet Laboratory, MIT, 170 Albany Street, Cambridge, MA 02139, USA.
J-B
JB
Laloë
Francis Bitter Magnet Laboratory, MIT, 170 Albany Street, Cambridge, MA 02139, USA.
J S
JS
Moodera
University of Bath, Department of Physics, Bath, BA2 7AY, UK.
S J
SJ
Bending