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-degrees from that predicted. At field inclinations greater than 80-degrees from the c axis, we find two instabilities into ordered, buckled rows of vortices, followed by a disordering transition.