Effect of pressure on the quantum spin ladder material IPA-CuCl3

Inelastic-neutron-scattering and bulk magnetic-susceptibility studies of the quantum S=1/2 spin ladder system (CH3)(2)CHNH3CuCl3 are performed under hydrostatic pressure. The pressure dependence of the spin gap Delta is determined. At P=1500 MPa it is reduced to Delta=0.79 meV from Delta=1.17 meV at ambient pressure. The results allow us to predict a soft-mode quantum phase transition in this system at P-c similar to 4 GPa. The measurements are complicated by the proximity of a structural phase transition that leads to a deterioration of the sample.