We present a comprehensive study of the effect of hydrostatic pressure on the
magnetic structure and spin dynamics in the spin-1/2 coupled ladder compound
C9​H18​N2​CuBr4​. The applied pressure is demonstrated as a parameter
to effectively tune the exchange interactions in the spin Hamiltonian without
inducing a structural transition. The single-crystal heat capacity and neutron
diffraction measurements reveal that the NeËŠel ordered state
breaks down at and above a critical pressure Pc​∼1.0 GPa through a
continuous quantum phase transition. The thorough analysis of the critical
exponents indicates that such transition with a large anomalous exponent η
into a quantum-disordered state cannot be described by the classic Landau's
paradigm. Using inelastic neutron scattering and quantum Monte Carlo methods,
the high-pressure regime is proposed as a Z2​ quantum spin liquid phase in
terms of characteristic fully gapped vison-like and fractionalized excitations
in distinct scattering channels.Comment: 6 pages and 4 figures in the main text. The Supplementary Material is
available upon the reques