Abstract
We introduce a promising new platform for Majorana zero-modes and various spintronics applications based on gate-defined wires in HgTe quantum wells. Due to the Dirac-like band structure for HgTe the physics of such systems differs markedly from that of conventional quantum wires. Most strikingly, we show that the subband parameters for gate-defined HgTe wires exhibit exquisite tunability: modest gate voltage variation allows one to modulate the Rashba spin-orbit energies from zero up to ~30K, and the effective g-factors from zero up to giant values exceeding 600. The large achievable spin-orbit coupling and g-factors together allow one to access Majorana modes in this setting at exceptionally low magnetic fields while maintaining robustness against disorder. As an additional benefit, gate-defined wires (in HgTe or other settings) should greatly facilitate the fabrication of networks for refined transport experiments used to detect Majoranas, as well as the realization of non-Abelian statistics and quantum information devices.
Highlights
The ability to efficiently manipulate electron spins with electric and magnetic fields underlies a wide variety of solid-state applications [1]
More surprising is the behavior of the effective g factors for confined subbands, which in contrast to typical wires are by far dominated by orbital contributions from the magnetic field
The physics we discuss here is unrelated to these edge states, but is instead close in spirit to the semiconductor wire proposals from Refs. [12,13].) We show that when a good proximity effect with an s-wave superconductor is generated, the giant g factors allow for exceptionally weak fields—a few tens of mT—to drive the wire into a topological superconductor with Majorana zero modes
Summary
The ability to efficiently manipulate electron spins with electric and magnetic fields underlies a wide variety of solid-state applications [1]. More surprising is the behavior of the effective g factors for confined subbands, which in contrast to typical wires are by far dominated by orbital contributions from the magnetic field (at least when directed normal to the well) These g factors undergo gate-induced oscillations and can be driven from zero to enormous values exceeding 600 due to orbital enhancement. The strong spin-orbit coupling for the HgTe wire (compared to typical electron-doped wires) further allows this topological state to possess a relatively large gap that exhibits enhanced immunity against disorder [46] Apart from these virtues, we expect that gate-defined wires offer another important longer-term advantage as well. Three appendixes contain additional calculations that further support the claims in this paper
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