Spin gap evolution upon Ca doping in the spin ladder series $Sr_{14-x}Ca_xCu_{24}O_{41}$ by inelastic neutron scattering

TL;DR

This study uses inelastic neutron scattering to show that the spin gap persists in Sr14-xCaxCu24O41 compounds up to x=13, revealing a stable singlet ground state and suggesting potential for magnetically-mediated pairing in a metallic spin ladder system.

Contribution

It provides the first systematic neutron scattering evidence that the spin gap survives Ca doping up to x=13, challenging previous NMR-based conclusions.

Findings

Spin gap persists up to x=13 in Ca-doped series.

Transition from localized to itinerant magnetism with doping.

Persistence of spin gap in metallic, normal state.

Abstract

The spin gap evolution upon Ca doping in Sr14-xCaxCu24O41 was systematically investigated using inelastic neutron scattering. We discover that the singlet-triplet spin gap excitation survives in this series with x up to 13, indicating the singlet dimer ground state in these compounds. This observation corrects the previous speculation that the spin gap collapses at x~13 by the NMR technique. The strong intensity modulation along QH in x=0 gradually evolves into a Q-independent feature in x>11. This could be attributed to the localized Cu moment magnetism developing into an itinerant magnetism with increasing x. It is a surprise that the spin gap persists in the normal state of this spin ladder system with metallic behaviour, which evidences the possibility of magnetically-mediated carrier pairing mechanism in a two-leg spin ladder lattice.