Transport properties of diluted magnetic semiconductors: Dynamical mean-field theory and Boltzmann theory

Abstract

The transport properties of diluted magnetic semiconductors (DMS) are calculated using dynamical mean field theory (DMFT) and Boltzmann transport theory. Within DMFT we study the density of states and the dc-resistivity, which are strongly parameter dependent such as temperature, doping, density of the carriers, and the strength of the carrier-local impurity spin exchange coupling. Characteristic qualitative features are found distinguishing weak, intermediate, and strong carrier-spin coupling and allowing quantitative determination of important parameters defining the underlying ferromagnetic mechanism. We find that spin-disorder scattering, formation of bound state, and the population of the minority spin band are all operational in DMFT in different parameter range. We also develop a complementary Boltzmann transport theory for scattering by screened ionized impurities. The difference in the screening properties between paramagnetic (T > Tc) and ferromagnetic (T < Tc) states gives rise to the temperature dependence (increase or decrease) of resistivity, depending on the carrier density, as the system goes from the paramagnetic phase to the ferromagnetic phase. The metallic behavior below Tc for optimally doped DMS samples can be explained in the Boltzmann theory by temperature dependent screening and thermal change of carrier spin polarization.

Optical properties of III-Mn-V ferromagnetic semiconductors

“…For example, the latter picture is not consistent with a non-monotonic behavior of the resistivity both in the limit of the lowest T and in the vicinity of the Curie temperature. [39,166,170,171,172] The totality of spectroscopic data discussed in subsections 3.1-3.4 support the view that the IB states preserve their identity derived from the d-character of Mn dopants even in the regime in which these states overlap with the VB on the metallic side of the metal-insulator transition. Conventional wisdom of heavily doped semiconductors teaches us that on the metallic side of the transition the impurity band and the host band merge into one inseparable band (see section 1.2).…”

“…Despite the substantial progress over the past decade, there are still a number of open questions in this field. In particular, the proper theoretical framework to describe the ferromagnetism that emerges in many III-TM-V materials still remains elusive [7,26,27,28,29,30,31,32,33,34,35,36,37,3,38,39]. The answer to this fundamental question has been hindered by a lack of consensus about the evolution of the electronic structure of III-TM-V compounds with TM doping.…”

Magnetotransport studies of mobility limiting mechanisms in undoped Si/SiGe heterostructures

“…Recent experiments focusing on quantum dots made in undoped Si/SiGe QWs [11][12][13][14] have consistently reached the single-electron regime and demonstrated inhomogeneous spin dephasing times T * 2 = 360 ns in naturally abundant Si, a substantial increase compared to GaAs spin qubits [3,14]. Further improvement of the Si/SiGe QW system may be feasible if the remaining mobility limiting mechanisms are clearly identified [15][16][17].…”

Metallic Behavior of Cyclotron Relaxation Time in Two-Dimensional Systems

“…Because the experimental data on Si-MOSFETs are in agreement with this theory, Anissimova et al argue that the 2D MIT is an interaction driven and N s -tuned quantum phase transition (QPT) [8]. From another point of view, ρ(T ) was calculated using the finite temperature Drude-Boltzmann theory by Das Sarma and Hwang [2,9,10]. The experimental data were quantitatively reproduced for different 2D systems by taking into account the temperature dependent screening of residual impurities.…”