Orbital Ordering in Low-Moment Ground-State of Parent Compounds in Iron-Based Superconductors

Abstract

Using a specific LDA+ U scheme, we perform first-principles calculations on non-doped iron based superconductor LaFeAsO in order to resolve a discrepancy of the antiferromagnetically ordered moment between standard first-principles calculations and experimental results. Consequently, it is found that two electronic states are stabilized in an intermediate U range. A quasi-stable state is the antiferromagnetically ordered one with the high magnetic moment ∼2.0 µ B equivalent with the previous calculation results, while the magnetic moment in the most stable state ∼0.3 µ B as obtained experimentally. The latter low-moment state exhibits a non-zero electric quadrupole moment originated from an orbital ordering. This latter result well explains various anomalous features as observed experimentally.