Oscillations of the Magnetoresistance and the Critical Current in MoGe Thin Films with Hole-arrays in Square Vortex-ice Geometry*

Resistivity measurements on MoGe thin films containing hole-arrays in square vortex-ice configuration were carried out to study the formation of a frustrated vortex state. MoGe thin films of 20 nm thick were prepared by sputter-deposition and holes with spacings of 200 nm - 400 nm and diameters from 100 nm to 300 nm were introduced into them using focused-ion-beam milling. We observed unusual matching effects: depending on the hole-hole spacing and the experimental temperature, the pinning enhancement at the half matching field can be stronger than that at the first matching field, as divulged by the deeper dip in the magnetoresistance and the higher peak in the critical current. Computer simulations within the nonlinear time-dependant Ginzburg-Landau theory reveal an origin of vortex jamming in the square vortex-ice state, indicating the first experimental realization of a square vortex-ice.