Measurements of the far-infrared magnetotransmission of YBa2(ZnxCu1-x)(3)O7
-delta thin film (x similar to 0.025) deposited on a wedged MgO substrate a
re reported. The application of magnetic field perpendicular to the ab plan
e produces at low temperature a linear increase of transmission for frequen
cies below similar to 30 cm(-1). We present a model of high-frequency vorte
x dynamics which qualitatively explains these results. (C) 2000 Elsevier Sc
ience B.V. All rights reserved.