VORTEX PINNING BY COMPETING DISORDER - BOSE-GLASS TO VORTEX-GLASS CROSSOVER

Magnetization measurements have been used to study the Bose-glass to v ortex-glass crossover in YBa2Cu3O7-x, crystals by varying the angle th eta between the field and the twin planes. Two critical angles theta(L ) and theta(K) are found: For theta < theta(L), vortices lock in to th e twin planes; for theta(L) < theta < theta(K), a kinked vortex struct ure occurs; for theta > theta(K), hysteresis loops reproduce the magne tic response of the untwinned regions where pinning is produced by ran dom point defects. The angles theta(K) and theta(L) depend only on the disorder in the untwinned regions and scale with [Delta M(theta(X))]( -0.5), where Delta M(theta(K)) is the hysteresis width for theta > the ta(K).