Metallic Spin Chains: the effect of Electronic Correlations

Much of what is known about one-dimensional systems comes from theories and experiments that are carried out on insulating spin chain systems where strong correlations localize electron moments, or alternatively on one-dimensional metals where correlations are very weak, and the electron states are fully delocalized.  There is considerable evidence in three-dimensional materials that varying the strength of electron correlations can lead to electronic localization, accompanied  by  T=0 quantum fluctuations between two Fermi surfaces with different sizes, one where electron states are included and one where they are not.  We seek experimental evidence that there is an analog of this sort of electronic localization in one-dimensional systems.  We focus our search on metallic systems, where the degree of hybridization between moment-bearing electrons and conduction electrons can have different strengths.   This talk will focus on the new compound Ti₄MnBi₂, which consists of chains of spin S=1/2 Mn atoms embedded in a metallic host.  Weak antiferromagnetic order is observed at 1.9 K,  where the ordered moment is ~10% of the Curie-Weiss moment.  Inelastic neutron scattering measurements find a nondispersing inelastic excitation below ~30 K, with no evidence for spin waves or spinons as expected in one-dimensional systems. The wave vector dependence of the inelastic scattering indicates that it is confined to small clusters, comparable to a unit cell.  Taken together, these results suggest that short ranged order along the chains appears near 30 K, although the chains fluctuate among states with differing singlet and triplet configurations. Interchain coupling is sufficiently strong to drive weak antiferromagnetic order at 1.9 K, although strong fluctuations along and among the chains continue to dominate within the antiferromagnetic phase.   The experimental evidence indicates that Ti₄MnBi₂ is a one-dimensional system,  although the magnetic excitations are strongly localized as might be expected  near a Mott transition.

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This research was supported by the National Science Foundation under grant DMR-1807451.