Topological Dirac states in asymmetric Pb1-xSnxTe quantum wells

The electronic structure of lead-salt (IV-VI semiconductor) topological quantum wells (T-QWs) is investigated with analytical solutions of the effective 4x4 Dimmock k & BULL; p model, which gives an accurate description of the bands around the fundamental energy gap. Specific results for three-layer Pb1-xSnxTe nanostructures with varying Sn composition are presented and the main differences between topological and normal (N) QWs highlighted. A series of new features are found in the spectrum of T-QWs, in particular in asymmetric QWs where large (Rashba spin-orbit) splittings are obtained for the topological Dirac states inside the gap

Electron g factor anisotropy in asymmetric III-V semiconductor quantum wells

The electron effective g factor tensor in asymmetric III-V semiconductor quantum wells (AQWs) and its tuning with the structure parameters and composition are investigated with envelope-function theory and the 8 x 8k . p Kane model. The spin-dependent terms in the electron effective Hamiltonian in the presence of an external magnetic field are treated as a perturbation and the g factors g(perpendicular to)* and g(parallel to)*, for the magnetic field in the QW plane and along the growth direction, are obtained analytically as a function of the well width L. The effects of the structure inversion asymmetry (SIA) on the electron g factor are analyzed. For the g-factor main anisotropy Delta g = g(perpendicular to)*-g(parallel to)*. in AQWs, a sign change is predicted in the narrow well limit due to SIA, which can explain recent measurements and be useful in spintronic applications. Specific results for narrow-gap AlSb/InAs/GaSb and AlxGa1-xAsGaAs/AlyGa1-yAs AQWs are presented and discussed with the available experimental data; in particular InAs QWs are shown to not only present much larger g factors but also a larger g-factor anisotropy, and with the opposite sign with respect to GaAs QWs

Heavily n-doped Ge: Low-temperature magnetoresistance properties on the metallic side of the metal-nonmetal transition

We report here an experimental and theoretical study on the magnetoresistance properties of heavily phosphorous doped germanium on the metallic side of the metal-nonmetal transition. An anomalous regime, formed by negative values of the magnetoresistance, was observed by performing low-temperature measurements and explained within the generalized Drude model, due to the many-body effects. It reveals a key mechanism behind the magnetoresistance properties at low temperatures and, therefore, constitutes a path to its manipulation in such materials of great interest in fundamental physics and technological applications. Published under license by AIP Publishing.Funding Agencies|Brazilian agency: CNPqNational Council for Scientific and Technological Development (CNPq) [303304/2010-3]; Brazilian agency: CAPESCAPES [PNPD 88882.306206/2018-01]; Brazilian agency: FAPESB [PNX 0007/2011, INT 0003/2015]; Brazilian agency: FAPESPFundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [15/16191-5]</p

Mesoscopic g-factor renormalization for electrons in III-V interacting nanolayers

The physics of the renormalization of the effective electron g factor by the confining potential in semiconductor nanostructures is theoretically investigated. The effective g factor for electrons in structures with interacting nanolayers, or coupled quantum wells (QWs), is obtained with an analytical and yet accurate multiband envelope-function solution, based on the linear 8 78k\ub7p Kane model for the bulk band structure. Both longitudinal and transverse applied magnetic fields are considered and the g-factor anisotropy (i.e., the difference between the two field configurations) is analyzed over the entire space spanned by the two structure parameters: the thickness of the active layers and the thickness of the tunneling barrier separating them. Two-dimensional anisotropy maps are constructed for symmetric and asymmetric InGaAs coupled QWs, with InP tunneling barriers, that reproduce exactly known single-layer or QW results, in different limits. The effects of the structure inversion asymmetry on the mesoscopic g-factor renormalization are also discussed, in particular the negative anisotropies for thin-layer structures. Such multilayer structures form an excellent testing ground for the theory, and the analytical solution presented, which is perfectly consistent over the whole space of parameters, leads to helpful expressions and can guide further research on the mechanisms of this mesoscopic renormalization