Ginzburg--Landau Analysis for the Antiferromagnetic Order in the Fulde--Ferrell--Larkin--Ovchinnikov Superconductor

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Antiferromangetic (AFM) order in the Fulde--Ferrell--Larkin--Ovchinnikov (FFLO) superconducting state is analyzed on the basis of the Ginzburg--Landau theory. To examine the possible AFM-FFLO state in a heavy fermion superconductor CeCoIn5, we focus on the incommensurate AFM order characterized by the wave vector \mbi{Q}=\mbi{Q}_{0}\pm\mbi{q}_{\text{inc}} with \mbi{Q}_{0}=(\pi,\pi,\pi) and \mbi{q}_{\text{inc}}\parallel[110] or [1\bar{1}0] in the tetoragonal crystal structure. We formulate the two component Ginzburg--Landau model to discuss two denerate incommensurate AFM states with \mbi{q}_{\text{inc}}\parallel[110] and [1\bar{1}0]. Owing to the broken translation symmetry in the FFLO state, multiple phase diagram of single-q phase and double-q phase is obtained under the magnetic field along [100] or [010]. Magnetic properties in each phase are investigated and compared with the neutron scattering and nuclear magnetic resonance (NMR) measurements. An ultrasonic measurement is proposed for a future experimental study on the possible AFM-FFLO state in CeCoIn5. The field orientation dependence of the AFM order in CeCoIn5 is discussed.
2011-09-15