Charge Dipolar Ordering in Yb Monopnictides

Abstract

Long-standing puzzling anomalous properties in Yb monopnictides are studied in detail with a novel new idea of paired Jahn-Teller distortion and charge dipolar ordering accompanied by compatible magnetic dipole ordering. The paired distortion occurs at around 50, K, commonly with an energy splitting of several meV. This is consistent with other systems that show similar paired Jahn-Teller distortion. Anomalous specific heat induced by level splitting, including the magnetic singlet ground state due to an antiferromagnetic pair exchange interaction, is observed as a two-peak structure with the lower peak around 5, K in common. A Néel transition at a low temperature of around 0.5, K in common is primarily a charge dipolar ordering due to pair ordering and occurs in competition with the pair singlet state, causing a weak transition with a small ordered moment. The above common features are caused by a strong-pair antiferromagnetic exchange interaction with nearly equal strengths.