Vibronic response of a spin-1/2 state from a carbon impurity in two-dimensional WS2

Abstract

We demonstrate the creation of a spin-1/2 state via the atomically controlled generation of magnetic carbon radical ions (CRIs) in synthetic two-dimensional transition metal dichalcogenides. Hydrogenated carbon impurities located at chalcogen sites introduced by chemical doping are activated with atomic precision by hydrogen depassivation using a scanning probe tip. In its anionic state, the carbon impurity exhibits a magnetic moment of 1 μB resulting from an unpaired electron populating a spin-polarized in-gap orbital. By inelastic tunneling spectroscopy and density functional theory we show that the CRI defect states couple to a small number of vibrational modes, including a local, breathing-type mode. The electron-phonon coupling strength critically depends on the spin state and differs for monolayer and bilayer WS2. These carbon radical ions in TMDs comprise a new class of surface-bound, single-atom spin-qubits that can be selectively introduced, are spatially precise, feature a well-understood vibronic spectrum, and are charge state controlled.

Engineering and probing atomic quantum defects in 2D semiconductors: A perspective

“…In Figure 3 we summarize different approaches we pursued to deliberately incorporate different types of defects with high specificity and density control, such as in-vacuo annealing 26 , chemical doping 24,27 , atom manipulation 28 and ion beam bombardment 29,30 . In particular we demonstrate substitutional doping with non-isovalent transition metals such as p-type V 31 and Nb 32 , or n-type Re 27,33 and Mn 34 during synthesis.…”

“…Generally, a defect's electronic 25,26,35 , optical 36 and magnetic spectrum 28 is determined by the electron configuration of the impurity, the coordination to the host lattice, charge-transfer from/to the substrate, and screening by the substrate. Moreover, spin-orbit coupling is a highly relevant interaction in these transition metal host crystal and compounds that leads to considerable defect state splitting as observed for the sulfur vacancy (VacS 26 ) and CrW 25 in WS2.…”

“…Moreover, spin-orbit coupling is a highly relevant interaction in these transition metal host crystal and compounds that leads to considerable defect state splitting as observed for the sulfur vacancy (VacS 26 ) and CrW 25 in WS2. Furthermore, point defects can strongly couple to phonons, which we analyzed in detail for a single carbon radical ion (CRI) in WS2 28 . The CRI exhibits a significant electron-phonon coupling, with a Huang Rhys factor of up to 5.4, for a dominant local vibrational mode.…”

“…Applying a voltage pulse at specific sites would then expose a dangling bond that could be used as an anchoring point for subsequently deposited atoms (Figure 5i). A first proof-of-principle of this concept has been demonstrated by STM-induced hydrogen desorption at CHS defects in WS2 introduced by a post-synthetic methane plasma treatment 28 . Despite these challenges ahead, 2D semiconductors offer exciting possibilities to engineer atomic quantum systems by chemical design principles from the bottom up.…”

Controllable Thin‐Film Approaches for Doping and Alloying Transition Metal Dichalcogenides Monolayers

“…It has been found that even with only CH-free molecules such as W(CO) 6 and H 2 Se involved in MOCVD of WSe 2 , the carbon impurities with a concentration of 225 ppm were still detected via STM/STS. [147] While carbon impurities could raise interesting spin properties [148] in 2D TMDs, it is imperative to remove them to minimize the impurity scattering and deep trap states in the devices made of TMDs. MBE can provide the cleanest synthetic crystals among all synthesis techniques because of its ultra-high vacuum growth environment and the use of high-purity elemental sources.…”