Citation: Zhou, Xiaocheng, Zhuhua Zhang, and Wanlin Guo. "Dislocations as single photon sources in two-dimensional semiconductors." Nano Letters 20.6 (2020): 4136-4143.
Web: https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.9b05305
Tags: Experimental, Hardware, Materials-applications
This review was written as a homework assignment for the "Materials 288A: quantum information science" class at UC Santa Barbara.
Single photon emitters are often plagued by vulnerabilities, coming from annealing and chemical passivization. To fix this, we should make a single photon emitter with built-in topological protection.
One prototype for this is building a single photon emitter of out of dislocations in two-dimensional semiconductors, as done in this paper. The semiconductors in mind are of the form MX_2, where M=Mo,W, and X=S,Se,Te. These are "transition metal dichalcogenidies" (TMDs). They are thin on the level of angstroms, and hence are known as two dimensional. Still, the thickness is quite notably measurable so these should not be considered two dimensional in the same way that fractional quantum Hall systems are.
Dislocations in such systems are in-plane shears cause by electric irradiation. These shears reduce symmetry, yielding two highly localized states near the Fermi level, one marked by bonding character and one marked by anti-bonding character. Radiative transitions on this two level system form the basis for our photon emitter.
The key is that dislocations themselves are not local - they are highly global effects. Hence, the induced two-layer system has global topological protection.
This paper outlines a number of reasons that these systems for particularly amenable to physical implementation. One reason given is that some of these systems will be stable when the Fermi energy is at an appropriate level for single photon emission, which is not at all the case for all proposed single photon emitters.