Pressure-Induced Magnetic Quantum Phase Transition in KCuCl3

Magnetization and neutron elastic scattering measurements under hydrostatic pressure were performed on KCuCl 3 , which is a three-dimensionally coupled spin dimer system with a gapped ground state. The spin gap decreases with increasing pressure. A quantum phase transition from a gapped singlet state to an antiferromagnetic state occurs at P c ≃8.2 kbar. For P > P c , the Neel temperature and the ordered moment increase with pressure. It was found that this quantum phase transition is caused by decrease in an intradimer interaction and increase in the sum of interdimer interactions with increasing pressure.