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. This review presents recent experimental and theoretical developments of the FFLO state mainly in heavy fermion superconductors. In particular we address the recently discovered quasi-two-dimensional superconductor CeCoIn5, which is a strong candidate for the formation of the FFLO state.

Water-soluble iron( 111) porphyrin and ferrihemoproteins (methemoglobin, metmyoglobin, oxidized cytochrome c, and catalase) associate with N O to yield the nitric oxide adducts. The equilibrium constants for association of ferrihemoproteins and N O are 1 order of magnitude larger than that of the water-soluble iron(II1) porphyrin which is free from protein, suggesting that the proteins offset the forward and backward reaction rates in the equilibrium reactions. Nanosecond laser photolysis studies of the nitric oxide adducts of metmyoglobin, oxidized cytochrome c, and catalase, (NO)MblI1, (NO)CytlI1, and (NO)CatlI1, have been carried out. The transient detected after laser flash photolysis of (NO)CatlI1 is identified as Cat"'. However, the transients observed for (NO)MblI1 and (NO)CytlI1 at 50 ns after laser pulsing are ascribed to MVI,, and Cytrrl,,, respectively, with the absorption spectra different from those of uncomplexed MblI1 and Cyt"'. In particular, the absorption spectrum of Cyt1Irtr markedly differs from that of the uncomplexed Cyt"'. The species MVrrtr and Cytrllt, are found to change to MblI1 and CytlI1, respectively, within a few microseconds. The quantum yields for the photodissociation of NO from nitric oxide adducts of ferrihemoproteins are 1 order of magnitude less than that from the N O adduct of the water-soluble iron(II1) porphyrin, probably due to fast geminate recombination reaction of N O and ferrihemoprotein in a heme pocket. The photochemistry of the nitric oxide adducts of hemoproteins and water-soluble iron(I1) porphyrin is also described on the basis of laser phosolysis studies.

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