Observation of spin gap in Pb2V3O9

Since the Bose-Einstein condensation (BEC) phenomenon was observed in the field-induced antiferromagnetic state of TlCuCl 3 , the BEC has attracted much interest from the aspect of quantum phase transition in the spin system. Very recently, we measured magnetic susceptibility and high field magnetization for ID spin chain system, Pb 2 V 3 O 9 , and found that the ground state of Pb 2 V 3 O 9 is of gapped spin singlet, which can be destroyed by the magnetic field above 5.2 T. This compound is thought to be a candidate for exhibiting BEC. As a result of magnetic measurements under high magnetic field, we have found a magnetic transition similar to the case of TlCuCl 3 , when we applied magnetic field above 5.6T to this compound.