Scanning-tunneling-microscopy study of distortion and instability of inclined flux-line-lattice structures in the anisotropic superconductor 2H-NbSe2

The tilted vortex lattice on the surface of 2H-NbSe2 is investigated with a scanning-tunneling microscope at magnetic fields, such that the vortex separation is comparable to or smaller than the magnetic penetration depth. The basis vectors show a distortion roughly consistent with bulk anisotropic London theory, however, their angular orientation with respect to the tilt direction differs by 30° from that predicted. At field inclinations greater than 80° from the c axis, we find two instabilities into ordered, buckled rows of vortices, followed by a disordering transition.