Takeshi Mizushima, Masahiro Takahashi, Kazushige Machida
We examine possible phase diagram in an H-T plane for Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in a two-band Pauli-limiting superconductor. We here demonstrate that as a consequence of the competition of two different modulation length scales, the FFLO phase is divided into two phases via the first order transition: Q_1- and Q_2-FFLO phases at the higher and lower fields. The Q_2-FFLO phase is further subdivided by successive first order transitions into the infinite family of FFLO subphases with rational modulation vectors, forming a devil's staircase structure for the field-dependence of the modulation vector and paramagnetic moment. The critical magnetic field above which the FFLO is stabilized gets lower than that in a single band superconductor, yet, tricritical Lifshitz point L at T_L is invariant under two-band parameter changes.
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http://arxiv.org/abs/1305.3678
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