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

Abstract

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.

Quasiparticle velocities in two-dimensional electron/hole liquids with spin-orbit coupling

“…33,34 For example, a surprisingly small Coulomb enhancement of the g-factor has been reported 33 and puzzling results have also been obtained for the effective masses m ± of the two hole-spin subbands (σ = ±). 34 A mechanism for the small g-factor enhancement was suggested in Ref. 31: if SOI strongly distorts the ground state spin structure, the exchange energy becomes ineffective in promoting full polarization of the hole system.…”

“…It can be seen in Table I that, while ∆ 0 does not change with r s , the interaction correction ∆ − ∆ 0 grows at lower densities (see Table I). Since experiments on hole systems can reach values as large as r s = 6 − 12, 33,34 it is reasonable to expect significant effects from δv ± in this low-density regime. As a reference, in electron systems, δv changes from ∼ 5% to −30% for r s ∼ 1 to 6.…”

Carrier-Density-Controlled Anisotropic Spin Susceptibility of Two-Dimensional Hole Systems

“…Size quantization strongly affects the holes' spin-3/2 degree of freedom [1]. This is believed to be the origin of an unusual paramagnetic response observed for quantum-well-confined holes [2][3][4], and the same phenomenon is expected to stabilize out-of-plane easy-axis magnetism in a dilute-magnetic-semiconductor (DMS) [5][6][7] two-dimensional (2D) hole system [8,9]. Controlling the confinement of holes thus enables appealing routes toward realizing magnetic semiconducting devices based on strain-induced anisotropies [10] or wavefunction engineering in heterostructures [11,12].…”

Controlling hole spins in quantum dots and wells

“…The need for a better understanding of this problem is highlighted by recent experiments on dilute hole liquids, in which strong correlations and spin-orbit coupling effects coexist. In this regime, these hole liquids show a significant deviation from the conventional behavior of two-dimensional electron liquids [25,26].…”

“…For a given travel time τ , the total travel distance and the separation between the two spin components are larger than the non-interacting value (∆ > δ). The difference in Fermi velocity of the two spin branches could be experimentally probed with transport measurements of the effective mass [112,26] and Raman scattering experiments [113], as well as by direct optical imaging of the wave-packet separation. In fact, for a travel distance of order ∼ µm, the travel time is 1 − 50 ps (depending on density) and typical values of γ for holes give spatial separations between the two spin components of a few hundred nm (∼ 200 nm for g = 0.1 and n = 3), which is within reach of Faraday rotation measurements [114,115].…”