Dynamics of a quasi-2D S=1/2 spin-dimer Heisenberg antiferromagnet under hydrostatic pressure

We present Inelastic Neutron Scattering measurements (INS) under hydrostatic pressure on a quasi-2D $S=1/2$ spin-dimer Heisenberg antiferromagnet. At high pressure, the observed dynamic structure factor $S(\vec{Q},\omega)$ features Goldstone modes, which is a key signature of long-range (magnetic) order. This is in good agreement with recent $\mu$SR findings and the presence of a pressure-induced quantum critical point at a moderate pressure [1]. Furthermore, we suggest an explanation for an apparent contradiction with a previous INS study performed under similar conditions [2].\newline \newline [1] M.~Thede \textit{et al.}, \textit{Phys.~Rev.~Lett.} \textbf{112}, 087204 \newline [2] T.~Hong \textit{et al.}, \textit{Phys.~Rev.~B} \textbf{82}, 184424