Zeeman effect in superconducting two-leg ladders: irrational magnetization plateaus and exceeding the Pauli limit.
The effect of a parallel magnetic field on superconducting two-leg ladders is investigated numerically. The magnetization curve displays an irrational plateau at a magnetization equal to the hole density. Remarkably, its stability is fundamentally connected to the existence of a well-known magnetic resonant mode. Once the zero-field spin gap is suppressed by the field, pairs acquire a finite momentum characteristic of a Fulde-Ferrell-Larkin-Ovchinnikov phase. In addition, Sz = 0 triplet superconducting correlations coexist with singlet ones above the irrational plateau. This provides a simple mechanism in which the Pauli limit is exceeded as suggested by recent experiments.
Roux
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Laboratoire de Physique Théorique, UMR5152 Université Paul Sabatier, 31062 Toulouse, France. roux@irsamc.ups-tsle.fr
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