Abstract
From small-angle neutron scattering studies of the flux line lattice (FLL) in CeCoIn5, with magnetic field applied parallel to the crystal c-axis, we obtain the field and temperature dependence of the FLL form factor (FF), which is a measure of the spatial variation of the field in the mixed state. We extend our earlier work (Bianchi et al 2008 Science 319 177) to temperatures up to 1250 mK. Over the entire temperature range, paramagnetism in the flux line cores results in an increase of the FF with field. Near Hc2 the FF decreases again, and our results indicate that this fall-off extends outside the proposed Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) region. Instead, we attribute the decrease to a paramagnetic suppression of Cooper pairing. At higher temperatures, a gradual crossover toward more conventional mixed state behavior is observed.
Highlights
Cooper pairs is suppressed, a phenomenon that is consistent with the predictions of recent numerical calculations [25]
Our results show that while we are unable to rule out a contribution to the field dependence of the form factor (FF) due to an FFLO-type state, the dominant contribution to the high-field fall in the FF at low temperature is due to a paramagnetic suppression of the Cooper pairing
The local field in the mixed state may be expressed as a sum over its spatial Fourier components with indices (h, k), and scattering vectors qhk belonging to the 2D flux line lattice (FLL) reciprocal lattice
Summary
A phenomenon that is consistent with the predictions of recent numerical calculations [25]. Our results show that while we are unable to rule out a contribution to the field dependence of the FF due to an FFLO-type state, the dominant contribution to the high-field fall in the FF at low temperature is due to a paramagnetic suppression of the Cooper pairing.
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