Daniel Weston, Egor Babaev
We classify ground states and normal modes for $n$-component superconductors with frustrated inter-component Josephson couplings, focusing on $n = 4$. The results should be relevant not only to multiband superconductors, but also to Josephson-coupled multilayers and Josephson-junction arrays. It was recently discussed that three-component superconductors can break time-reversal symmetry as a consequence of phase frustration. We discuss how to classify superconductors with an arbitrary number of components. Although already for the four-component case there is a large number of different combinations of phase-locking and phase-antilocking Josephson couplings, we establish that there is a much smaller number of equivalence classes where properties of frustrated multicomponent superconductors can be mapped to each other. This classification is related to the graph-theoretical concept of Seidel switching. Numerically, we calculate ground states, normal modes and characteristic length scales for the four-component case. We report conditions of appearance of new continuous ground-state degeneracies which do not correspond to broken symmetries.
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http://arxiv.org/abs/1306.3179
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