Anomalous diamagnetism of electride electrons in transition metal silicides

Intermetallic silicide compounds, LaScSi and ${\mathrm{Y}}_{5}{\mathrm{Si}}_{3}$, known for being hydrogen (H) storage materials, are drawing attention as candidates for electrides in which anions are substituted by unbound electrons. It is inferred from a muon spin rotation experiment that the local field at the muon site (which is the same site as that for H) in these compounds exhibits a large negative shift under an external magnetic field, which is mostly independent of temperature. Such anomalous diamagnetism signals a unique property of electride electrons associated with transition metals. Moreover, the diamagnetic shift decreases with increasing H content, suggesting that the electride electrons existing coherently in the hollow interstitial positions are adsorbed by H to form hydride ions $({\mathrm{H}}^{\ensuremath{-}})$.