Hole-spin mixing in InAs quantum dot molecules

Abstract

Holes confined in single InAs quantum dots have recently emerged as a promising system for the storage or manipulation of quantum information. These holes are often assumed to have only heavy-hole character and further assumed to have no mixing between orthogonal heavy hole spin projections (in the absence of a transverse magnetic field). The same assumption has been applied to InAs quantum dot molecules formed by two stacked InAs quantum dots that are coupled by coherent tunneling of the hole between the two dots. We present experimental evidence of the existence of a hole spin mixing term obtained with magneto-photoluminescence spectroscopy on such InAs quantum dot molecules. We use a Luttinger spinor model to explain the physical origin of this hole spin mixing term: misalignment of the dots along the stacking direction breaks the angular symmetry and allows mixing through the light-hole component of the spinor. We discuss how this novel spin mixing mechanism may offer new spin manipulation opportunities that are unique to holes.

Hole spin relaxation in InAs/GaAs quantum dot molecules

“…This value corresponds to a DQD with large yet realistic lateral offset. [42] All calculations are carried out at a magnetic field B = 2 T. Figure 2 illustrates the energy spectra and hole spin lifetimes of a DQD with interdot distance d = 3 nm as a function of the external electric field F z . An analysis of the lowenergy hole states reveals that they have mainly HH character.…”

“…These anticrossings form so-called spin-hot spots (see, e.g., [43]), where spin mixing is maximized. While the strong spin mixing can be benefitial for spin control protocols [42], our calculatios show that it also leads to severely reduced T 1 .…”

“…Energetically, the main consequence of introducing a lateral offset to the QDs position is a reduction in the hole tunneling which, in turn, diminishes the magnitude of the charge anticrossing in the energy spectrum. [42] As for the hole spin lifetimes, by comparing with figure 2(c), figure 2(d) shows that misalignment of the QDs roughly preserves the shape of T 1 estimated from either H L or H BIA , but it causes an additional decrease in T 1 of one order of magnitude or more.…”

Origin of two-hole triplet splitting in circular quantum dots

“…[24] The suitability of positively charged trions is not clear a priori, as the valence band spin-orbit interaction can lead to significant hole spin mixing. [14,25,26] To address this question we calculate the expectation value of the hole spin in single-hole and two-hole states. The results are shown in Fig.…”

“…Circular dots are not only of fundamental interest -realistic self-assembled QDs often present but small deviations from this ideal limit-, but also of practical importance, as highly symmetric QDs are desirable for spintronic applications to minimize spin admixture through spin-orbit interaction. [13,14,15] Holes are described as Luttinger spinors resulting from a 4-band k·p Hamiltonian. We find that HH-LH coupling gives rise to large splittings of the p-shell even if the QDs have perfect circular symmetry, and show that this follows from the unequal centrifugal energy of the minor components in p + and p − states.…”