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.