Metal-insulator transition and orbital state of quasi-one-dimensional vanadium system

为了揭示准一维BaVS_3在70 K下的金属-绝缘体转变机制，我们主要利用角分辨光电子能谱（ARPES）和软X射线吸收线性二向色谱（LD）研究了转变过程中V_（3d）态的变化. ARPES研究表明，a1 g轨道在150 - 120 K形成能隙，远高于70 K，由于一维不稳定性，而egp轨道由于局域化仅在70 K形成能隙。另一方面，LD研究表明，V 3d轨道的占有率在整个过渡过程中保持不变。LD谱的理论分析表明，V链的3d轨道符合egp-egp-egp-a1 g沿着序排列.

In order to reveal the mechanism of metal - insulator transition of quasi-one-dimensional BaVS3 at 70 K, we have investigated the change of the V 3d state across the transition mainly by means of angle-resolved photoemission spectroscopy (ARPES) and soft x-ray absorption linear dichroism spectroscopy (LD). ARPES studies revealed that the a1g orbital forms a gap at 150 - 120 K, far above 70 K, due to one-dimensional instability, while the egp orbital forms a gap just at 70 K due to localization. LD studies, on the other hand, revealed that the occupancy ratio of the V 3d orbitals is unchanged across the transition. Theoretical analyses of the LD spectra highly suggest that the V 3d orbitals aligns with egp-egp-egp-a1g order along the V chain.