Evidence for a spin pseudogap in the normal state of superconductingMo3Sb7

Abstract

Using muon spin relaxation (μSR) and inelastic neutron scattering (INS) we have investigated the normal state of the superconductorMo3Sb7 and the referencecompound Ru3Sn7. The μSR experiments on Ru3Sn7 reveal static and relatively slow dynamic relaxations, which are ascribed to a random staticnuclear dipole field and thermally activated muon motion, respectively. INS experiments onRu3Sn7, on the other hand, reveal three phononic excitations at 11, 18 and 23 meV,substantiating the assertion of Einstein and Debye oscillations derived fromthe specific heat and electrical resistivity data. The distinct difference in theμSR as well as INSspectra between Ru3Sn7 and Mo3Sb7 provides strong evidence for a magnetic/electronic nature of the phase transition atT* = 50 K in the Mo-based compound. On the basis of theμSR and INS data, the energy spin pseudogap of 150(10) K was estimated.The observed weak magnetism in the dynamic susceptibilityχ′′(Q,ω) and residual longitudinal field relaxation at 5 K imply a static ordering or quantumfluctuations.