Evidence for a Field-Induced Quantum Phase Transition in Ising-like D-Er₂Si₂O₇

Exploring the magnetic properties of the rare-earth pyrosilicate (RE₂Si₂O₇) family of compounds is of interest due to their variety of crystal structures and anisotropic pseudo-spin ½ moments. D-Er₂Si₂O₇ (space group P2₁/b) was previously found to have a large g-tensor anisotropy (g_xx = 2.6, g_yy = 3.4, g_zz = 13.4) and magnetization consistent with Ising exchange [1]. In this work we have performed specific heat, magnetometry, and inelastic neutron scattering (INS) on a polycrystalline sample to further characterize the magnetism of D-Er₂Si₂O₇. The zero-field specific heat and magnetometry data corroborate previous measurements indicating antiferromagnetic ordering at 1.9 K. The INS data shows a gapped excitation at 0.6 meV in zero field, consistent with Ising exchange. This gap closes with the application of a magnetic field of ~1 T, consistent with a quantum critical point. Magnetization measurements on single crystal samples suggest that the mode softening is due to the field acting on the direction perpendicular to the Ising moments. Our data suggests that D-Er₂Si₂O₇ could be a new experimental system in which to study the quantum Ising model.
[1] M. J. M. Leask, P. R. Tapster, and M. R. Wells, J. Phys. C Solid State Phys. 19, 1173 (1986).