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Here we present a comprehensive neutron scattering study on a spin-1/2 coupled ladder antiferromagnet C₉H₁₈N₂CuBr₄ (DLCB for short) under applied hydrostatic pressure. In DLCB, the inter-ladder coupling is sufficiently strong to drive the system to the long-range antiferromagnetic ordering phase below T_N=2 K [1]. Analysis of the spin Hamiltonian suggests that DLCB is close to the quantum critical point in two dimensions at ambient pressure and zero field [2]. Single-crystal neutron diffraction measurements under pressure suggest that the magnetic order breaks down above a ciritical pressure P_c~1.0 GPa. By contrasting with quantum Monte Carlo calculations of the dynamic structure factor, the follow-up inelastic neutron scattering study above P_c reveals evidence of a gapped spin-liquid phase with the Z₂ topological order, characterized by excitation spectra of fully gapped visons and deconfined spinons.

References:
[1] T. Hong et al., Phys. Rev. B 89, 174432 (2014).
[2] T. Hong et al., Nat. Phys. 13, 638 (2017).