Department of Physics, Renmin University of China, Beijing 100872, People's Republic of China.
J Phys Condens Matter. 2013 Sep 11;25(36):365501. doi: 10.1088/0953-8984/25/36/365501. Epub 2013 Aug 8.
From first-principles calculations, we have studied the electronic and magnetic structures of compound Na2Ti2Pn2O (Pn=As or Sb), whose crystal structure is a bridge between or a combination of those of high-Tc superconducting cuprates and iron pnictides. We find that in the ground state Na2Ti2As2O is a novel blocked checkerboard antiferromagnetic semiconductor with a small band gap of about 0.15 eV. In contrast, Na2Ti2Sb2O is a bi-collinear antiferromagnetic semimetal, with a small moment of about 0.5 μ(B) around each Ti atom. We show that there is a strong Fermi surface nesting in Na2Ti2Pn2O, and we verify that the blocked checkerboard and bi-collinear antiferromagnetic states both are the spin density waves induced by the Fermi surface nesting. A tetramer structural distortion is found in company with the formation of a blocked checkerboard antiferromagnetic order, in good agreement with the experimentally observed commensurate structural distortion but with space group symmetry retained after the anomaly happens.
从第一性原理计算出发，我们研究了化合物 Na2Ti2Pn2O（Pn=As 或 Sb）的电子和磁结构，其晶体结构是高温超导铜酸盐和铁磷化物之间的桥梁或组合。我们发现，在基态下，Na2Ti2As2O 是一种新型的具有约 0.15eV 小能隙的被阻塞的棋盘反铁磁半导体。相比之下，Na2Ti2Sb2O 是一种双共线反铁磁半导体，每个 Ti 原子周围有大约 0.5μB 的小磁矩。我们表明，在 Na2Ti2Pn2O 中存在强的费米面嵌套，并且验证了被阻塞的棋盘和双共线反铁磁态都是由费米面嵌套诱导的自旋密度波。我们发现，在形成被阻塞的棋盘反铁磁有序的同时存在四聚体结构畸变，这与实验观察到的共位结构畸变非常吻合，但在异常发生后保持了空间群对称性。
