Layered pnictide-oxide Na2Ti2Pn2O (Pn=As, Sb): a candidate for spin density waves.
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.
Department of Physics, Renmin University of China, Beijing 100872, People's Republic of China.
Xun-Wang
XW
Yan
Zhong-Yi
ZY
Lu