Disorder, spin-orbit, and interaction effects in diluteGa1−xMnxAs

Abstract

We derive an effective Hamiltonian for Ga1−xMnxAs in the dilute limit, where Ga1−xMnxAs can be described in terms of spin F = 3/2 polarons hopping between the Mn sites and coupled to the local Mn spins. We determine the parameters of our model from microscopic calculations using both a variational method and an exact diagonalization within the so-called spherical approximation. Our approach treats the extremely large Coulomb interaction in a non-perturbative way, and captures the effects of strong spin-orbit coupling and Mn positional disorder. We study the effective Hamiltonian in a mean field and variational calculation, including the effects of interactions between the holes at both zero and finite temperature. We study the resulting magnetic properties, such as the magnetization and spin disorder manifest in the generically non-collinear magnetic state. We find a well formed impurity band fairly well separated from the valence band up to xactive < ∼ 0.015 for which finite size scaling studies of the participation ratios indicate a localization transition, even in the presence of strong on-site interactions, where xactive < xnom is the fraction of magnetically active Mn. We study the localization transition as a function of hole concentration, Mn positional disorder, and interaction strength between the holes.

Carrier-induced ferromagnetism in diluted local-moment systems

“…If the ferromagnetic ordering is mediated by 'free' carriers, its origin is assumed to be of RKKY type 18 . However, further results show that RKKY interaction between the localized spins is insufficient 3,4,19,20,21,22 . Korringa-KohnRostock CPA (KKR-CPA) calculations 23,24 show that the ground state of Ga 1−x Mn x As is half-metallic.…”

“…In addition, the measured saturated magnetization is observed to be much less than the nominal concentration of Mn ions 2 . Experimentally, the remanence magnetization and the Curie temperature T C are both enhanced by post-growth annealing of the samples, which changes positions of defects and the hole concentration 3,4 . So the magnetism in DMSs is heavily affected by material issues, e.g.…”

Combined Approach of Density Functional Theory and Quantum Monte Carlo Method to Electron Correlation in Dilute Magnetic Semiconductors

“…4, we show local density of states around the Mn site defined by NðrÞ ¼ Àd=dhnðrÞ À nð1Þij ¼0:05 eV , where nðrÞ is the electron number operator at site r. The highly anisotropic distribution of local density of states around Mn is consistent with the STM measurements, 15,21) which again emphasizes the necessity of including both the band structure and correlation effect. 22,23) The anisotropy of local density of state is originated from the anisotropic mixing energy V k;i in eq. (1).…”

Spatial Structure of Mn-Mn Acceptor Pairs in GaAs

“…Furthermore, recent Raman scattering experiments suggest that a Mn 2 3d 4 configuration partially occurs for x > 0:02 [16]. Recent theories suggest significant modifications in the ferromagnetic properties of Ga 1ÿx Mn x As if the holes reside in a strongly disordered impurity band [11,[17][18][19][20]. If the Mn density is near the metal-insulator transition, and individual Mn dopants states are weakly hybridizing with each other, then the inhomogeneous hole density of the impurity band measured by X-STM near an individual Mn dopant should closely resemble that of an isolated neutral Mn, only weakly perturbed by Mn-Mn interactions.…”