OBSERVATION OF ANOMALOUS ESR MODE OF CSCUCL3 IN SUBMILLIMETER-WAVE REGION

Submillimeter wave ESR has been performed from 90 to 380 GHz for CsCuCl3 using the pulsed magnetic fields up to 15 T in the temperature range from 1.8 to 86 K. In the ordered phase below T(N)=10.5 K, shift of the ESR mode from that in the conventional mean field theory including Dzyaloshinsky-Moriya interaction has been observed for H//c above the critical field H(c) where a small jump in the magnetization occurs. These anomalies cannot be understood in terms of the mean field theory and will be discussed in connection with a new theory proposed by Shiba and Nikuni which suggests that the quantum effect is responsible for the anomalies at H(c).