Direct physical observation of the FFLO state in CeCoIn5
A famous prediction (by Fulde & Ferrell and Larkin & Ovchinnikov: FFLO) is for a spatially-modulated superconducting state in any material where the effect of high magnetic fields on the antiparallel spins of electrons in Cooper pairs places an upper limit on the field at which superconductivity can occur (¿Pauli-limited superconductivity¿). There have been various indirect, macroscopic indications of the FFLO state in Pauli-limited materials but no direct observation, and suggestions that an analogous state can occur in cold atom condensates. The FFLO state should appear below the upper critical field at low temperatures. In the more stable LO version, it contains planes of zeroes of the superconducting order parameter. These planes are perpendicular to the magnetic field, and slice through the flux line lattice (FLL) which is also present. The nonzero momentum of the Cooper pairs represented by this spatially-modulated state arises because the two halves of a Cooper pair have different Zeeman energy in the magnetic field, and therefore must have a compensating difference in their kinetic energy and momentum. We propose to search for FFLO in CeCoIn5 using a novel SANS geometry.
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FORGAN Edward M.; BLACKBURN Elizabeth; CAMPILLO Emma; CUBITT Robert; M. R. Eskildsen; FURUKAWA K. Hazuki; SODA Minoru and WHITE Jonathan. (2021). Direct physical observation of the FFLO state in CeCoIn5. Institut Laue-Langevin (ILL) doi:10.5291/ILL-DATA.5-42-559
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