Abstract
Hole spins have gained considerable interest in the past few years due to their potential for fast electrically controlled qubits. Here, we study holes confined in Ge hut wires, a so-far unexplored type of nanostructure. Low-temperature magnetotransport measurements reveal a large anisotropy between the in-plane and out-of-plane g-factors of up to 18. Numerical simulations verify that this large anisotropy originates from a confined wave function of heavy-hole character. A light-hole admixture of less than 1% is estimated for the states of lowest energy, leading to a surprisingly large reduction of the out-of-plane g-factors compared with those for pure heavy holes. Given this tiny light-hole contribution, the spin lifetimes are expected to be very long, even in isotopically nonpurified samples.
Highlights
The interest in group IV materials for spin qubits has been continuously increasing over the past few years after the demonstration of long electron spin decay times.[1−5] Silicon (Si) has the advantage of being the most important element in semiconductor industry; it can be isotopically purified, eliminating the problem of decoherence from hyperfine interactions
A light-hole admixture of less than 1% is estimated for the states of lowest energy, leading to a surprisingly large reduction of the out-of-plane g-factors compared with those for pure heavy holes
A solution to this problem can come from a second type of SK Ge nanostructures, the hut clusters, which were observed for the first time in 1990.28 Zhang et al.[29] showed in 2012 that under appropriate conditions, the hut clusters can expand into Ge hut wires (HWs), with lengths exceeding 1 μm
Summary
Interesting perspective, not much is known about their electronic properties. Here, we study three-terminal devices fabricated from Ge HWs. The strong confinement and the strain change the gaps between the various bands of the semiconductor, which (among other things) may lead to a substantial rescaling of the effective band structure parameters.[38] Improvements can be expected from an extended model that involves the split-off band and the conduction band.[34,41,42] our assumption of an infinite HW with a rectangular cross-section is a reasonable approximation for the elongated HW QDs realized here, the details of the confinement (and the strain) along all spatial directions can provide additional corrections Taking all these elements fully into account is beyond the scope of the present work and requires extensive numerics.
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