Neutron scattering and pairing mechanisms in underdoped cuprate ladder Sr2.5Ca11.5Cu24O41

We present inelastic neutron scattering data on the cuprate ladder Sr2.5Ca11.5Cu24O41, showing both the high and low-energy excitations at 5 K and 120 K. We also perform DMRG simulations of doped and undoped ladders. Comparing simulation to experiment shows signatures of spin-charge interplay in the magnetic excitations which can be understood by a one-band Hubbard model. We also observe a gap emerging at low temperatures giving evidence for electron pairing, as well as signatures of charge ordering between ladders. This excellent correspondence between theory and experiment suggests the Luther-Emery pairing mechanism is relevant in the cuprate ladders, and potentially for the 2D cuprate superconductors as well.