Structural Distortion Stabilizing the Antiferromagnetic and Semiconducting Ground State of BaMn2As2

Abstract

Abstract:We report evidence that the experimentally found antiferromagnetic structure as well as the semiconducting ground state of BaMn 2 As 2 are caused by optimally-localized Wannier states of special symmetry existing at the Fermi level of BaMn 2 As 2 . In addition, we find that a (small) tetragonal distortion of the crystal is required to stabilize the antiferromagnetic semiconducting state. To our knowledge, this distortion has not yet been established experimentally.

Structural Distortion Stabilizing the Antiferromagnetic and Insulating Ground State of NiO

“…Because NiO is a prototype Mott insulator [5,6,21], the magnetic super band of NiO is evidently half filled, and the Mott condition is evidently satisfied in this band. As mentioned, I already found a magnetic super band in the band structure of BaMn 2 As 2 [17]. In fact, also BaMn 2 As 2 is a band gap insulator, often referred to as a small band gap semiconductor [22,23].…”

“…The results of this paper corroborate that the nonadiabatic atomic-like motion defined within the NHM is physically existent if the considered metal possesses a narrow, partly filled band with suitable Wannier functions (Section 5.1). The success in the last 40 years in identifying narrow, roughly half filled superconducting [9,27] and magnetic [9,17] bands in the conventional band structures of superconducting and magnetic materials provides evidence that the nonadiabatic atomic-like motion as defined in the NHM actually has physical reality and stabilizes the superconducting and magnetic states, respectively, in these materials. In addition, our results on NiO and BaMn 2 As 2 [17] suggested that "magnetic super bands" (Section 6) may stabilize insulating ground states in a magnetic phase.…”

“…This is achieved by exactly the one distortion of the crystal illustrated in Figure 2: The Ni atoms are shifted in the ±(T 2 − T 3 ) direction from their positions at the lattice points t Ni in Equation (17), realizing in this way the group M 9 in the sense that the two commutator relations (14) and (16) are satisfied. With our group-theoretical methods, we cannot determine the magnitude of the displacements; however, they are clearly not so large as plotted (for the sake of clarity) in Figure 2a.…”

“…respectively. An energy band with Wannier functions of the first type (i) and the second type (ii) we called "magnetic band related the the magnetic group M" and "superconducting band", respectively (Definitions 16 and 22 of [9]), because the strongly correlated nonadiabatic atomic-like motion in a magnetic band and in a superconducting band evidently stabilizes magnetism [10,16,17] and superconductivity [18,19], respectively. While superconducting bands are not the subject of this paper, the meaning of magnetic bands shall be clarified as follows: Condition 2.…”

“…Such an active band I already found in the band structure of BaMn 2 As 2 [17] and called it the "magnetic super band": Definition 1. The Bloch functions of a magnetic super band related to the magnetic group M can be unitarily transformed into optimally localized Wannier functions symmetry adapted to M in such a way that the Wannier functions are not only centered at the atoms bearing the magnetic moments, but are centered at all the atoms of the material.…”