Instability of a triangular Abrikosov lattice at values of the Ginzburg-Landau parameter kappa close to unity

The “soft” transverse mode of gapless excitations related to the deformation of a triangular Abrikosov lattice with a single flux quantum per unit cell at an arbitrary value of the Ginzburg–Landau parameter κ is investigated. An Abrikosov lattice with the angle φ = π/3 between the unit cell vectors is shown to be unstable in a narrow range of values, 1 < κ < 1.000634. The excitation spectrum of the mode under consideration at low values of the momentum k (in the k 2 approximation) is isotropic at k lying in a plane perpendicular to the magnetic field.