Uniaxial pressure dependencies of the phase boundary of TlCuCl₃

We present a thermal expansion and magnetostriction study of TlCuCl_3, which shows a magnetic-field induced transition from a spin gap phase to a Neel ordered phase. Using Ehrenfest relations we derive huge and strongly anisotropic uniaxial pressure dependencies of the respective phase boundary, e.g. the transition field changes by about $\pm 185$ GPa depending on the direction of uniaxial pressure.