FARINFRARED AND MIDINFRARED SPECTRUM OF YBA2CU3O6.0 IN HIGH MAGNETIC-FIELDS

The far- and mid-infrared spectrum of antiferromagnetic YBa2Cu3O6.0 wa s investigated by infrared transmission measurements ((k) over right a rrow parallel to c-axis) in high magnetic fields up to 16.5 Tesla. at T=1K. A peak at 1436 cm(-1) which previously was assigned to the excit ation of single optical magnons did not show a measurable shift with m agnetic field. In the far-infrared, no signature of acoustic magnon ab sorption has been observed in the magneto transmittance. However, at 8 3 cm(-1) the sixth phonon of symmetry E(u) in YBa(2)Cu(3)O6.0 has been found.