Magnetic excitations in a tuneable S = 1/2 spin ladder system near quantum criticality

Spin ladders are excellent model systems for studying quantum phase transitions, as they exhibit a quantum critical point between non-magnetic spin singlet dimers to Néel magnetic order as inter-ladder exchange is increased. Ba2CuTeO6 is a Cu2+ S = 1/2 two-leg spin ladder system, that is close to the quantum critical point on the Néel ordered side. By replacing Te with W in a Ba2CuTe1-xWxO6 solid solution, we have managed to suppress the magnetic order as indicated by muon spin rotation measurements. We will use inelastic neutron scattering to study magnetic excitations in these doped samples. This will allow us to establish whether we have succeeded in stabilizing a spin singlet ground state and to study quantum criticality near the QCP.