Imaging of vortex lattice in single crystal YNi2B2C by STM

The vortex lattice in YNi2B2C has been observed through the measurements of the local quasi-particle density of states with low temperature scanning tunneling microscopy and spectroscopy. The vortex lattice has shown the hexagonal to the square lattice transition around 0.1T under the magnetic field applied along the c-axis. On the other hands, under the magnetic field along the a-axis, the transition has occurred at much higher magnetic field of 1.0T. We have also observed that the vortex lattice gets disordered above 2.0T.