OBSERVATION OF TILT INDUCED ORIENTATIONAL ORDER IN THE MAGNETIC-FLUX LATTICE IN 2H-NBSE2

We report on observations of the magnetic flux lattice in 2H-NbSe2 using the magnetic decoration technique. For low applied magnetic fields and with the field applied parallel to the c axis of the crystal, we find a disordered flux lattice with short-ranged positional and orientational order. As the tilt angle of the applied magnetic field increases, we find that the orientational order in the flux lattice grows dramatically. At high tilt angles, we find a hexatic solid with long-ranged orientational order but only short-ranged positional order. This is the first observation of a flux lattice in which the orientational order is stabilized by changing the tilt angle of the applied magnetic field in an anisotropic superconductor.