Commensurate vortex lattices pinned by a periodic lattice of columnar defects

The effects of a periodic hexagonal lattice of columnar defects on the curv es of magnetic induction B(H), vortex-lattice melting T-m(H) and critical c urrent density J(c)(H) versus external field H are investigated, including the effects of vortex interaction, thermal and quantum fluctuations, an app lied current drive and columnar pin disorder. It is found theoretically tha t the smallest slope of B(H) occurs when the magnetic induction B matches t he regular pinning field n(pin)phi(0) over a finite range of H. This commen suration leads to an inhibition of the vortex-lattice melting and a large e nhancement of the critical current density, i.e., the curves of T-m(H) and J(c)(H) each have a series of broad plateaus. The applied current drive, el ectric field-like in form, shifts this melting curve downwards. J(c)(T) is the power-3/2 temperature decay at intermediate temperatures and decays exp onentially to zero at high temperatures. The pin disorder and ion stragglin g reduce these favourable effects and wash out the plateaus when they becom e equal to certain critical values.