On the character of states near the Fermi level in (Ga,Mn)As: impurity to valence band crossover
T. Jungwirth, Jairo Sinova, A. H. MacDonald, B. L. Gallagher, V. Novak, K. W. Edmonds, A. W. Rushforth, R. P. Campion, C. T. Foxon, L. Eaves, K. Olejnik, J. Mas… 展开作者
T. Jungwirth, Jairo Sinova, A. H. MacDonald, B. L. Gallagher, V. Novak, K. W. Edmonds, A. W. Rushforth, R. P. Campion, C. T. Foxon, L. Eaves, K. Olejnik, J. Masek, S. -R. Eric Yang, J. Wunderlich, C. Gould, L. W. Molenkamp, T. Dietl, H. Ohno
We discuss the character of states near the Fermi level in Mn doped GaAs, as revealed by a survey of dc transport and optical studies over a wide range of Mn concentrations. A thermally activated valence band contribution to dc transport, a mid-infrared peak at energy hbar omega approx 200 meV in the ac- conductivity, and the hot photoluminescence spectra indicate the presence of an impurity band in low doped (<<1% Mn) insulating GaAs:Mn materials. Consistent with the implications of this picture, both the impurity band ionization energy inferred from the dc transport and the position of the mid-infrared peak move to lower energies and the peak broadens with increasing Mn concentration. In metallic materials with > 2% doping, no traces of Mn-related activated contribution can be identified in dc-transport, suggesting that the impurity band has merged with the valence band. No discrepancies with this perception are found when analyzing optical measurements in the high-doped GaAs:Mn. A higher energy (hbar omega approx 250 meV) mid-infrared feature which appears in the metallic samples is associated with inter-valence band transitions. Its red-shift with increased doping can be interpreted as a consequence of increased screening which narrows the localized-state valence-band tails and weakens higher energy transition amplitudes. Our examination of the dc and ac transport characteristics of GaAs:Mn is accompanied by comparisons with its shallow acceptor counterparts, confirming the disordered valence band picture of high-doped metallic GaAs:Mn material.
Disorder Enhanced Spin Polarization in Diluted Magnetic Semiconductors
我们提出了一个稀磁半导体的理论研究，其中包括一个现实的主机能带结构内的自旋轨道耦合，并明确治疗由于随机取代Mn离子的无序的影响。自旋-轨道耦合通过混合价带中不同的自旋态降低了自旋极化，而Mn离子的无序增强了自旋极化，这是由于铁磁杂质团簇和杂质束缚态的形成。无序导致对形成杂质带以及与价带杂化的空穴载流子的大的影响。对于Mn掺杂0.01 < x < 0.04，系统是具有大有效质量和低迁移率的金属。
Weak localization in GaMnAs: evidence of impurity band transport
本文报道了铁磁半导体GaMnAs在低温（$T<3$ K）和低磁场（$0< B <20$ mT）下的负磁阻效应。我们将这种效应归因于弱本地化。弱局域化的观测提供了这些材料中杂质带输运的强有力证据，因为对于价带输运，人们预期由于强自旋-轨道相互作用而导致的弱反局域化或由内禀磁化干扰的完全抑制。除了弱局域化外，我们还观察到了Altshuler-Aronov电子-电子相互作用效应。
