Pressure-induced structural transition in copper pyrazine dinitrate and implications for quantum magnetism

We combined synchrotron-based infrared and Raman spectroscopies, diamond anvil cell techniques, and first principles calculations to unveil pressure-induced distortions in quasi-one-dimensional Cu(pyz)(NO3)2. The crossover at 0.7 GPa is local in nature whereas the transition at 5 GPa lowers symmetry from Pmna to P2221 and is predicted to slightly increase magnetic dimensionality. Comparison with prior magnetoinfrared results reveals the striking role of out-of-plane bending of the pyrazine ligand, a finding that we discuss in terms of the possibility of using pressure to bias the magnetic quantum critical transition in this classic S=1/2 antiferromagnet.