Spin-Valley Locking for In-Gap Quantum Dots in a MoS₂ Transistor

Abstract

Spins confined to atomically thin semiconductors are being actively explored as quantum information carriers. In transition metal dichalcogenides (TMDCs), the hexagonal crystal lattice gives rise to an additional valley degree of freedom with spin-valley locking and potentially enhanced spin life and coherence times. However, realizing well-separated single-particle levels and achieving transparent electrical contact to address them has remained challenging. Here, we report well-defined spin states in a few-layer MoS2 transistor, characterized with a spectral resolution of ∼50 μeV at T el = 150 mK. Ground state magnetospectroscopy confirms a finite Berry-curvature induced coupling of spin and valley, reflected in a pronounced Zeeman anisotropy, with a large out-of-plane g-factor of g ⊥ ≃ 8. A finite in-plane g-factor (g ∥ ≃ 0.55–0.8) allows us to quantify spin-valley locking and estimate the spin–orbit splitting 2ΔSO ∼ 100 μeV. The demonstration of spin-valley locking is an important milestone toward realizing spin-valley quantum bits.

Excited state spectroscopy and spin splitting in single layer MoS2 quantum dots

“…S and Mo vacancies in MoS 2 ) which appear as in-gap states and observed in the subthreshold region. 34 The first Coulomb peak in our device appears at V bg = 10 V (Fig. 2A) whereas the threshold voltage appears at V bg ∼ 6 V (Fig.…”

“…This varying g -factor and associated anisotropy between different diamonds has been observed for point defects in thick MoS 2 as a result of spin-valley locking of the spin states. 34 These effects are predicted to be enhanced in SL MoS 2 . Zeeman splitting in the current experiment was measured at T = 1 K which limits the low B-field resolution.…”

Perfect Zeeman Anisotropy in Rotationally Symmetric Quantum Dots with Strong Spin–Orbit Interaction

“…As shown in the Supporting Information, even when changing the external B -field direction away from the ring axis, such that interaction via SOI should be enhanced in points ii and iii, almost no splitting is found due to the different orbital character of the states. This indicates a tunable orbital protection from spin-flips and also highlights a possible spin–orbital analogy to spin-valley physics studied in materials with valley degrees of freedom, such as silicon, graphene, , carbon nanotubes, , and transition metal dichalcogenides. , …”

Symmetry Breaking and Spin–Orbit Coupling for Individual Vacancy-Induced In-Gap States in MoS2 Monolayers

“…Chalcogen vacancies are the most prevalent naturally occurring point defects in TMDCs. , In-gap states due to sulfur (S) vacancies in MoS 2 give rise to its ubiquitous n -type doping and can allow it to bind excitons in DX 0 centers, giving rise to defect-induced or single-photon emission. , Spin–valley locking for in-gap states has been detected in a large valley Zeeman effect and Zeeman anisotropy . Spectroscopic signatures of in-gap states ,, and photon emission from individual vacancy defects have been captured at the atomic scale by scanning tunneling microscopy (STM).…”

“…More recently, atomically thin van-der-Waals (vdW) semiconductors and insulators have emerged as candidate platforms for optoelectronics applications , and quantum technologies. , In the semiconducting transition metal dichalcogenides (TMDCs), this is due to their large and direct band gap in the monolayer limit, , strong spin–orbit coupling, and additional valley degree of freedom, with spin–valley coupling. − Point defects in TMDCs have been identified to introduce strongly confined electronic bound states within the bandgapin-gap states − that can inherit these properties, promising applications as optically and electrically addressable quantum systems.…”