Role of CuO chains in vortex core structure in YBa(2)Cu(3)O(7-delta)

The Bogoliubov-deGennes equations are solved for a proximity model for YBa(2)Cu(3)O(7-delta) in a magnetic field. The model explicitly includes the effects of the one-dimensional CuO chains, whose influence on the vortex core structure is studied. The rapid vortex core contraction as a function of field, which is seen experimentally at low magnetic fields, is naturally explained by the presence of the chains.