HIGH-FIELD HEAT-CAPACITIES OF SOME SINGLET GROUND-STATE SYSTEMS AT VERY-LOW TEMPERATURES

Several aspects of high field heat capacity observed in different type s of singlet ground state system are discussed, The ground state energ y gap and its magnetic field dependence are also studied in the Haldan e gap compounds NENP, NINO and TMNIN. The origin of the observed minim um gap in applied magnetic field is discussed. In the spin-Peierls com pound CuGeO3, the energy gap of the Cu2+ spin system in the dimerized phase and the gapless state in the high-field magnetic phase are confi rmed.