Pressure-induced magnetic quantum phase transition from gapped ground state in TlCuCl3

Magnetization measurements under hydrostatic pressure were performed on an S = 1/2 coupled spin dimer system TlCuCl3 with a gapped ground state under magnetic field H parallel to the [201] direction. With increasing applied pressure P, the gap decreases and closes completely at P-c = 0.42 +/- 0.05 kbar. For P > P-c, TlCuCl3 undergoes antiferromagnetic ordering. A spin-flop transition was observed at H-sf similar or equal to 0.7 T. The spin-flop field is approximately independent of pressure, although the sublattice magnetization increases with pressure. The gap and Neel temperature are presented as functions of pressure. The occurrence of the pressure-induced quantum phase transition is attributed to the relative enhancement of the interdimer exchange interactions compared with the intradimer exchange interaction.