Role of finite layer thickness in spin polarization of GaAs two-dimensional electrons in strong parallel magnetic fields

Tutuc, Emanuel; Melinte, Sorin; Poortere, E. P. De; Shayegan, M.; Winkler, Roland

doi:10.1103/physrevb.67.241309

Cited by 72 publications

(83 citation statements)

References 18 publications

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“…Indeed, this increase is yet significantly larger than the increase of m * one would expect for an electron system with nominally similar values of m * and g * due to the coupling of B to the holes' orbital motion. 18 In the latter case we would expect a roughly 50% enhancement of m * (compared to its B = 0 value). On the other hand, according to recent measurements 24-27 whose results were supported by subsequent calculations, 28,29 m * is suppressed in a 2D electron system which is fully spin polarized.…”

Section: Discussion Of Effective Mass Datamentioning

confidence: 99%

“…The measured m * is close to the value measured when B = 0 and does not appear to be affected by the large B which should in principle couple to the holes' orbital motion and lead to an increase in m * . 18 Finally, from the value of B at which the minority spin subband is depopulated, we deduce a value for the 2D holes' spin susceptibility which is about 50% enhanced with respect to the band value.…”

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“…In the highly interacting, dilute regime (r s > ∼ 3), χ * and m * are typically enhanced compared to the band values and increase with increasing r s , as confirmed both theoretically [1][2][3][4][5][6][7][8] and experimentally. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Besides r s , the spin and/or valley degrees of freedom also play an important role in the re-normalization of m * and χ * since they modify the exchange interaction. 5,6,17,[24][25][26][27] In particular, it was recently demonstrated that when a 2D electron system is fully spin and valley polarized, m * is suppressed compared to its band value.…”

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Effective mass and spin susceptibility of dilute two-dimensional holes in GaAs

et al. 2011

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We report effective hole mass (m * ) measurements through analyzing the temperature dependence of Shubnikov-de Haas oscillations in dilute (density p ∼ 7 × 10 10 cm −2 , rs ∼ 6) two-dimensional (2D) hole systems confined to a 20 nm-wide, (311)A GaAs quantum well. The holes in this system occupy two nearly-degenerate spin subbands whose m * we measure to be ∼ 0.2 (in units of the free electron mass). Despite the relatively large rs in our 2D system, the measured m * is in reasonably good agreement with the results of our energy band calculations which do not take interactions into account. We then apply a sufficiently strong parallel magnetic field to fully depopulate one of the spin subbands, and measure m * for the populated subband. We find that this latter m * is close to the m * we measure in the absence of the parallel field. We also deduce the spin susceptibility of the 2D hole system from the depopulation field, and conclude that the susceptibility is enhanced by about 50% relative to the value expected from the band calculations.

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Section: Discussion Of Effective Mass Datamentioning

confidence: 99%

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Effective mass and spin susceptibility of dilute two-dimensional holes in GaAs

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“…10). The narrow QW 2DES should be closest to an "ideal" 2D system (except for disorder of course): (i) only one valley is occupied, (ii) the in-plane Fermi contour is circular and therefore isotropic, (iii) it is very narrow (QW width ≅ 4.5 nm) so that finite layer thickness corrections 44 should be negligible, and (iv) the dilute limit can be reached relatively easily because the electron effective mass for this system (m t * = 0.20) is reasonably large compared to, e.g., m* = 0.067 for GaAs 2D electrons, so that large values of r s , the average inter-electron distance measured in units of the effective Bohr radius, can be attained. We found that at a given r s this 2DES exhibits the largest enhancement of χ s among all the 2DESs and, even more remarkably, the enhancement is in excellent agreement with the results of quantum Monte Carlo calculations 45 without any adjustable parameters (Fig.…”

Section: Spin Susceptibility Of Alas 2d Electronsmentioning

confidence: 99%

Two‐dimensional electrons occupying multiple valleys in AlAs

Shayegan

Poortere

Gunawan

et al. 2006

Physica Status Solidi (b)

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Two-dimensional electrons in AlAs quantum wells occupy multiple conduction-band minima at the Xpoints of the Brillouin zone. These valleys have large effective mass and g-factor compared to the standard GaAs electrons, and are also highly anisotropic. With proper choice of well width and by applying symmetry-breaking strain in the plane, one can control the occupation of different valleys thus rendering a system with tuneable effective mass, g-factor, Fermi contour anisotropy, and valley degeneracy. Here we review some of the rich physics that this system has allowed us to explore.

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“…This simply reflects the fact that, thanks to the finite thickness of the electron layer, the energies of the X and Y valleys slightly shift with respect to each other as B increases. The shift comes about because the parallel field couples to the orbital motion of the electrons [33,34] and changes the confinement energies of the X and Y valleys. Since X and Y valleys have anisotropic Fermi contours which are orthogonal to each other, the parallel field, which is applied along the major axis of one valley (X) and perpendicular to the other (Y ), couples differently to these valleys, causing a slight shift in their relative energies.…”

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Spin–valley phase diagram of the two-dimensional metal–insulator transition

et al. 2007

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Using symmetry breaking strain to tune the valley occupation of a two-dimensional (2D) electron system in an AlAs quantum well, together with an applied in-plane magnetic field to tune the spin polarization, we independently control the system's valley and spin degrees of freedom and map out a spin-valley phase diagram for the 2D metal-insulator transition. The insulating phase occurs in the quadrant where the system is both spin-and valley-polarized. This observation establishes the equivalent roles of spin and valley degrees of freedom in the 2D metal-insulator transition.PACS numbers: 71.30.+h, 73.43.Qt, 73.50.Dn, The scaling theory of localization in two dimensions [1], which predicts an insulating phase for two-dimensional electron systems (2DESs) with arbitrarily weak disorder, was challenged by the observation of a metallic temperature dependence (dρ/dT > 0) of the resistivity, ρ, in low-disorder Si metal-oxide-semiconductor field-effect transistors (Si-MOSFETs) [2]. The associated metal-toinsulator transition (MIT) has subsequently become the subject of intense interest and controversy [3]. While behavior similar to that of Ref.[2] has now been reported for a wide variety of 2D carrier systems such as n-AlAs, 10], and p-Si/SiGe [11,12], the origin of the metallic state and its transition into the insulating phase remain major puzzles in solid state physics.Several experiments have demonstrated the important role of the spin degree of freedom in the MIT problem, either in systems with a strong spin-orbit interaction [10,13,14], or via the application of an external magnetic field to spin polarize the carriers [15,16,17,18,19]. The latter experiments have shown that a magnetic field applied parallel to the 2DES plane suppresses the metallic temperature dependence, ultimately driving the 2DES into the insulating regime as the 2DES is spin polarized. The relevance of multiple conduction-band valleys, on the other hand, is less known. Although it has been discussed theoretically that the occupation of multiple valleys may also be important [20,21], there has been no direct experimental demonstration. Here we show that the electrons' valley degree of freedom indeed plays a crucial role, analogous to that of spin. We study a 2DES, confined to an AlAs quantum well, in which we can independently tune both the spin and valley degrees of freedom. By studying the temperature dependence of ρ at various degrees of spin and valley polarization, we map out the metal-insulator phase diagram in this system at a constant density. The 2DES exhibits a metallic behavior when either the valley or spin are left fully unpolarized, and a minimum amount of both spin and valley polarization is required to enter the insulating phase.We performed experiments on 2DESs confined to modulation-doped, AlAs quantum wells of width 11 nm and 15 nm [22]. In these systems, the electrons occupy two conduction-band valleys of AlAs centered at the edges of the Brillouin zone along the [100] and [010] directions. We denote these valleys as X and Y...

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Role of finite layer thickness in spin polarization of GaAs two-dimensional electrons in strong parallel magnetic fields

Cited by 72 publications

References 18 publications

Effective mass and spin susceptibility of dilute two-dimensional holes in GaAs

Effective mass and spin susceptibility of dilute two-dimensional holes in GaAs

Two‐dimensional electrons occupying multiple valleys in AlAs

Spin–valley phase diagram of the two-dimensional metal–insulator transition

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