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 (CH{sub 3}){sub 2}CHNH{sub 3}CuCl{sub 3} 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{sub c} {approx} 4 GPa. The measurements are complicated by the proximity of a structural phase transition that leads to a deterioration of the sample.