Critical temperatures of the two-band model for diluted magnetic semiconductors

Abstract

Using Dynamical Mean Field Theory (DMFT) and Monte Carlo (MC) simulations, we study the ferromagnetic transition temperature (Tc) of a two-band model for Diluted Magnetic Semiconductors (DMS), varying coupling constants, hopping parameters, and carrier densities. We found that Tc is optimized at all fillings p when both impurity bands (IB) fully overlap in the same energy range, namely when the exchange couplings J and bandwidths are identical. The optimal Tc is found to be about twice larger than the maximum value obtained in the one-band model, showing the importance of multiband descriptions of DMS at intermediate J's.

Optical properties of diluted magnetic semiconductors in coherent potential approximation

“…The agreement between CPA and MC results, as it was noted in Ref. [19], is due to the fact that at weak and intermediate couplings, the carriers can be sufficiently delocalized that a smearing effect may occur and considering the disorder only in average appears to be sufficient. Moreover, since the actual value of Kondo coupling and the carrier density are not known experimentally with precision, it is difficult to quantitavely compare the calculated results with experiments.…”

Temperature dependent magnetization of the two band model for diluted magnetic semiconductors

“…The magnetization curves are convex, but some look different from the classic textbook Weiss form. The T c is maximal for both n when the bands fully overlap (J 2 /J 1 = 1) which agrees with [6,7]. In Figs.…”

“…As was noted in Ref. [6], the explanation is straightforward: at n = x in the one band model the IB is fully occupied leading to a vanishing T c , but for the same n in the two band model both bands are half filled, which ultimately leads to the highest value for T c and M (T ). In summary, in this paper the coherent potential approximation has been applied to the twoband model for DMS.…”

“…In addition, for over doping of the carriers, T c decreases to zero. Recently the critical temperature was calculated using a two band model for DMS by Monter Carlo (MC) technique, dynamical mean field theory (DMFT) and coherent potential approximation (CPA) [6][7]. The main finding is that the maximal T c of the two band model is found when both impurity bands (IB) fully overlap and this value is approximately twice larger than the highest T c obtained in the single band model.…”

Diluted Ferromagnetic Semiconductors—Theoretical Aspects

“…The issue how various corrections to the mean-field p-d Zener model (Dietl et al, 2000) affect theoretical values of T C was recently examined in some detail for (Ga,Mn)As (Brey and Gómez-Santos, 2003;Timm and MacDonald, 2005;Jungwirth et al, 2005;Popescu et al, 2006) with the conclusions that the overall picture remains quantitatively valid. Figure 3 shows one of the recent theoretical modelings of T C in comparison to experimental findings for (Ga,Mn)As .…”