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Quantum Hall ferromagnetism in two-dimensional electron gases

Grant number: 05/04777-3
Support type:Scholarships in Brazil - Doctorate (Direct)
Effective date (Start): July 01, 2006
Effective date (End): December 31, 2010
Field of knowledge:Physical Sciences and Mathematics - Physics - Condensed Matter Physics
Principal researcher:José Carlos Egues de Menezes
Grantee:Gerson Ferreira Júnior
Home Institution: Instituto de Física de São Carlos (IFSC). Universidade de São Paulo (USP). São Carlos , SP, Brazil


A number of experimental groups [e.g. V. Piazza et al., Nature 402, 638(1999), De Poortere et al., Science 290, 546 (2000)] have reported the observation of hysteretic phenomena in the magneto-transport properties of two-dimensional electron gases (2DEGs). Ubiquitous spikes and dips have been seen in longitudinal Rxx and Hall Rxy resistances in these systems in the quantum Hall regime. There is only one theoretical work on the subject [Jungwirth and MacDonald, Phys. Rev. Lett. 87, 216801 (2001)] qualitatively explaining some of the observed features in terms of domain walls. Recently, we have put forward a theory for the existence of hysteretic phenomena in the magneto-transport of magnetic 2DEGs (Freire and Egues, cond-mat/0412491) without including domain walls. Our description quantitatively accounts for all the hysteretic features observed in Rxx in Mn-based quantum wells containing a partially spin-polarized 2DEG this proposal. Here we present research plans to extend and apply our alternate description for magneto-transport in 2DEGs in the quantum Hall ferromagnetic regime, to a variety of novel systems: non-magnetic 2DEGs in single quantum wells, quantum Hall bilayers and spin-orbit coupled 2DEGs. For non-magnetic 2DEGs in single wells, there is a vast amount of experimental data not fully understood, e.g., the physical origin of the dips and peaks in the Hall plateaus. The additional bilayer (pseudo-spin) degree of freedom allows us to investigate a variety of distinct Landau level crossings leading to quantum Hall ferromagnetism and hysteresis in double wells. The interplay of interlayer electron tunneling and the inter- and intra-layer Coulomb interaction give rise to novel electronic states not present in single-layer systems. Interestingly, 2DEGs with spin orbit have not been investigated in the literature so far. The interplay of Coulomb and the spin-orbit interactions should lead to interesting magneto-transport phenomena. The state-of-the-art systems we intend to tackle here should allow us to thoroughly investigate quantum Hall ferromagnetism and magneto-transport in 2DEGs in a controllable manner. The technique we will use is the Spin Density Functional Theory (SDFT) with a Local Spin Density Approximation (LSDA) formulated within the framework of the usual effective-mass approximation. By considering the finite-temperature formulation of Mermin, we minimize Helmholtz free energy of the 2DEG to derive the corresponding set of Kohn-Sham equations. Our Kohn-Sham set accounts for spin and orbital effects (i.e., Zeeman and Landau quantization). Many-body effects (exchange and correlation, XC) are included via a spin-dependent XC potential as parametrized by Vosko et al. [Can. J. Phys. 58, 1200 (1980), this is one of the standard parameterizations in the literature]. We will solve the self-content Kohn-Sham set (including Poisson's equation) by finite differencing within a grid with variable spacing. This implementation builds upon the IC project successfully carried out by Gerson Ferreira Jr. (FAPESP, Proc. 04/09790-5) and the PhD thesis of Dr. Henrique J. P. Freire (FAPESP, Proc. 1999/06868-3). We anticipate no difficulties with the numerical implementation of our self-consistent scheme. Specific problems to be investigated: Non-magnetic 2DEGs: we should investigate in detail the physical origin of the hysteretic dips and peaks appearing in the Hall resistance Rxy and their connection with the spikes in the longitudinal magneto-resistance Rxx. Understanding the mechanisms which control these features will allow us to suggest specific experiments to probe the dips and peaks systematically. We should look at the effects of inter-layer tunneling and inter- and intra-layer Coulomb correlation on the magneto-transport properties of the system, in particular the hysteretic phenomena (dips and peaks) in Rxy and Rxx. Spin-orbit coupled 2DEGs: we will determine Rxy and Rxx for the first time here. (AU)

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Academic Publications
(References retrieved automatically from State of São Paulo Research Institutions)
FERREIRA JÚNIOR, Gerson. Quantum Hall ferromagnetism via density functional theory. 2011. Doctoral Thesis - Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT) São Carlos.

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