VORTEX TELEGRAPH NOISE IN HIGH MAGNETIC-FIELDS

We cool untwinned single crystals of YBa2Cu3O7-delta with columnar def ects down to liquid-He temperatures and study the development of pinni ng in the strongly interacting Bose glass with local Hall-probe magnet ometry. We are able to resolve discrete fluctuations in the local vort ex density resulting from reconfigurations of the vortex assembly betw een metastable states nearby in energy. By varying the applied magneti c field, and therefore the mean vortex density, we gain microscopic in formation about vortex-vortex interactions. [S0163-1829(97)52142-4].