Vortex tilt modulus in Fulde-Ferrell-Larkin-Ovchinnikov state

Vortex tilt response in a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) vortex lattice is studied as a probe reflecting the spatial structure of this state. In quasi 2D materials under a parallel magnetic field, the tilt modulus E2 of the nodal planes in the FFLO state modulating along the field decreases as the paramagnetic effect is effectively enhanced, and this reduction of E2 in turn reduces the vortex tilt modulus. This reduction, more remarkable in higher fields or in more 2D-like systems, of vortex tilt modulus upon entering the FFLO state may be one origin of an anomalous anisotropic reduction of sound velocity detected in an ultrasound measurement in CeCoIn5.