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Texture in the Superconducting Order Parameter of Heavy Fermion Compound


The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is a novel superconducting state in a strong magnetic field characterized by the
formation of  Cooper pairs with nonzero total momentum (k, -k+q),  instead of the ordinary BCS pairs (k, -k).  A fascinating aspect of the
FFLO state is that it exhibits inhomogeneous superconducting phases with  a spatially oscillating order parameter and spin polarization. The FFLO
state has been of interest in various research fields, not only in superconductors in solid state physics, but also in neutral Fermion
superfluid of ultracold atomic gases and in color superconductivity in high energy physics. In spite of extensive studies of various
superconductors, there has been no undisputed experimental verification  of the FFLO state, mainly because of the very stringent conditions
required of the superconducting materials.  Among several classes of  materials, certain heavy fermion and organic superconductors are
believed to provide conditions that are favorable to the formation of  the FFLO state.  Here I discuss recent experimental and theoretical
developments of the FFLO state mainly in heavy fermion superconductors.    In particular I address the recently discovered quasi-two-dimensional
superconductor CeCoIn5, which is a candidate for the formation of the FFLO state.